This allows operations that are marked Custom, but have some type
combinations that are legal to get past this code.
Add custom mutation code to X86's Select function for the nodes
that don't have isel patterns yet.
This seems to be causing some performance regresions that I'm
trying to investigate.
One thing that stands out is that this transform can increase
the live range of the operands of the earlier logic op. This
can be bad for register allocation. If there are two logic
op inputs we should really combine the one that is closest, but
SelectionDAG doesn't have a good way to do that. Maybe we need
to do this as a basic block transform in Machine IR.
llvm-svn: 373401
Summary:
This adds the ISD opcode and a DAG combine to create it. There are
probably some places where we can directly create it, but I'll
leave that for future work.
This updates all of the isel patterns to look for this new node.
I had to add a few additional isel patterns for aligned extloads
which we should probably fix with a DAG combine or something. This
does mean that the broadcast load folding for avx512 can no
longer match a broadcasted aligned extload.
There's still some work to do here for combining a broadcast of
a broadcast_load. We also need to improve extractelement or
demanded vector elements of a broadcast_load. I'll try to get
those done before I submit this patch.
Reviewers: RKSimon, spatel
Reviewed By: RKSimon
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68198
llvm-svn: 373349
There's room from improvement here, but this is a decent
starting point.
There are a few minor regressions in the vector-rotate tests,
where we are now forming a vpternlog from an and before we get
a chance to form it for a bitselect that we were matching
previously. This results in an AND and an ANDN feeding the
vpternlog where previously we just had an AND after the
vpternlog. I think we can probably DAG combine the AND with
the bitselect to get back to similar codegen.
llvm-svn: 373172
This allows us to reduce the use count on the condition node before
the match. This enables load folding for that operand without
relying on the peephole pass. This will be improved on for
broadcast load folding in a subsequent commit.
This still requires a bunch of isel patterns for vXi16/vXi8 types
though.
llvm-svn: 373156
The attached test case would previous infinite loop after
r365711.
I'm going to move this to X86ISelDAGToDAG.cpp to get the setcc
to match VPTEST in 32-bit mode in a follow up commit.
llvm-svn: 372543
Summary:
PR43381 notes that while we are good at matching `(X >> C1) & C2` as BEXTR/BEXTRI,
we only do that if we either have BEXTRI (TBM),
or if BEXTR is marked as being fast (`-mattr=+fast-bextr`).
In all other cases we don't match.
But that is mainly only true for AMD CPU's.
However, for all the CPU's for which we have sched models,
the BZHI is always fast (or the sched models are all bad.)
So if we decide that it's unprofitable to emit BEXTR/BEXTRI,
we should consider falling-back to BZHI if it is available,
and follow-up with the shift.
While it's really tempting to do something because it's cool
it is wise to first think whether it actually makes sense to do.
We shouldn't just use BZHI because we can, but only it it is beneficial.
In particular, it isn't really worth it if the input is a register,
mask is small, or we can fold a load.
But it is worth it if the mask does not fit into 32-bits.
(careful, i don't know much about intel cpu's, my choice of `-mcpu` may be bad here)
Thus we manage to fold a load:
https://godbolt.org/z/Er0OQz
Or if we'd end up using BZHI anyways because the mask is large:
https://godbolt.org/z/dBJ_5h
But this isn'r actually profitable in general case,
e.g. here we'd increase microop count
(the register renaming is free, mca does not model that there it seems)
https://godbolt.org/z/k6wFoz
Likewise, not worth it if we just get load folding:
https://godbolt.org/z/1M1deGhttps://bugs.llvm.org/show_bug.cgi?id=43381
Reviewers: RKSimon, craig.topper, davezarzycki, spatel
Reviewed By: craig.topper, davezarzycki
Subscribers: andreadb, hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D67875
llvm-svn: 372532
This reverts r372314, reapplying r372285 and the commits which depend
on it (r372286-r372293, and r372296-r372297)
This was missing one switch to getTargetConstant in an untested case.
llvm-svn: 372338
This broke the Chromium build, causing it to fail with e.g.
fatal error: error in backend: Cannot select: t362: v4i32 = X86ISD::VSHLI t392, Constant:i8<15>
See llvm-commits thread of r372285 for details.
This also reverts r372286, r372287, r372288, r372289, r372290, r372291,
r372292, r372293, r372296, and r372297, which seemed to depend on the
main commit.
> Encode them directly as an imm argument to G_INTRINSIC*.
>
> Since now intrinsics can now define what parameters are required to be
> immediates, avoid using registers for them. Intrinsics could
> potentially want a constant that isn't a legal register type. Also,
> since G_CONSTANT is subject to CSE and legalization, transforms could
> potentially obscure the value (and create extra work for the
> selector). The register bank of a G_CONSTANT is also meaningful, so
> this could throw off future folding and legalization logic for AMDGPU.
>
> This will be much more convenient to work with than needing to call
> getConstantVRegVal and checking if it may have failed for every
> constant intrinsic parameter. AMDGPU has quite a lot of intrinsics wth
> immarg operands, many of which need inspection during lowering. Having
> to find the value in a register is going to add a lot of boilerplate
> and waste compile time.
>
> SelectionDAG has always provided TargetConstant for constants which
> should not be legalized or materialized in a register. The distinction
> between Constant and TargetConstant was somewhat fuzzy, and there was
> no automatic way to force usage of TargetConstant for certain
> intrinsic parameters. They were both ultimately ConstantSDNode, and it
> was inconsistently used. It was quite easy to mis-select an
> instruction requiring an immediate. For SelectionDAG, start emitting
> TargetConstant for these arguments, and using timm to match them.
>
> Most of the work here is to cleanup target handling of constants. Some
> targets process intrinsics through intermediate custom nodes, which
> need to preserve TargetConstant usage to match the intrinsic
> expectation. Pattern inputs now need to distinguish whether a constant
> is merely compatible with an operand or whether it is mandatory.
>
> The GlobalISelEmitter needs to treat timm as a special case of a leaf
> node, simlar to MachineBasicBlock operands. This should also enable
> handling of patterns for some G_* instructions with immediates, like
> G_FENCE or G_EXTRACT.
>
> This does include a workaround for a crash in GlobalISelEmitter when
> ARM tries to uses "imm" in an output with a "timm" pattern source.
llvm-svn: 372314
Encode them directly as an imm argument to G_INTRINSIC*.
Since now intrinsics can now define what parameters are required to be
immediates, avoid using registers for them. Intrinsics could
potentially want a constant that isn't a legal register type. Also,
since G_CONSTANT is subject to CSE and legalization, transforms could
potentially obscure the value (and create extra work for the
selector). The register bank of a G_CONSTANT is also meaningful, so
this could throw off future folding and legalization logic for AMDGPU.
This will be much more convenient to work with than needing to call
getConstantVRegVal and checking if it may have failed for every
constant intrinsic parameter. AMDGPU has quite a lot of intrinsics wth
immarg operands, many of which need inspection during lowering. Having
to find the value in a register is going to add a lot of boilerplate
and waste compile time.
SelectionDAG has always provided TargetConstant for constants which
should not be legalized or materialized in a register. The distinction
between Constant and TargetConstant was somewhat fuzzy, and there was
no automatic way to force usage of TargetConstant for certain
intrinsic parameters. They were both ultimately ConstantSDNode, and it
was inconsistently used. It was quite easy to mis-select an
instruction requiring an immediate. For SelectionDAG, start emitting
TargetConstant for these arguments, and using timm to match them.
Most of the work here is to cleanup target handling of constants. Some
targets process intrinsics through intermediate custom nodes, which
need to preserve TargetConstant usage to match the intrinsic
expectation. Pattern inputs now need to distinguish whether a constant
is merely compatible with an operand or whether it is mandatory.
The GlobalISelEmitter needs to treat timm as a special case of a leaf
node, simlar to MachineBasicBlock operands. This should also enable
handling of patterns for some G_* instructions with immediates, like
G_FENCE or G_EXTRACT.
This does include a workaround for a crash in GlobalISelEmitter when
ARM tries to uses "imm" in an output with a "timm" pattern source.
llvm-svn: 372285
See D66309 for context.
This is the first sweep of x86 target specific code to add isAtomic bailouts where appropriate. The intention here is to have the switch from AtomicSDNode to LoadSDNode/StoreSDNode be close to NFC; that is, I'm not looking to allow additional optimizations at this time.
Sorry for the lack of tests. As discussed in the review, most of these are vector tests (for which atomicity is not well defined) and I couldn't figure out to exercise the anyextend cases which aren't vector specific.
Differential Revision: https://reviews.llvm.org/D66322
llvm-svn: 371547
As reported in post-commit review of r370327,
there is some case where the code crashes.
As discussed with Craig Topper, the problem is that getConstant()
internally calls getSplatBuildVector(), so we don't insert
the constant itself.
If we do that manually we're good.
llvm-svn: 371346
We can use a MOVSX16 here then rely on FixupBWInst to change to
MOVSX32 if the upper bits are dead. With a special case to
not promote if it could be turned into CBW.
Then we can rely on X86MCInstLower to turn the MOVSX into CBW
very late if register allocation worked out.
Using MOVSX gives an opportunity to use the MOVSX as a both a
copy and a sign extend since the input and output register aren't
tied together.
Differential Revision: https://reviews.llvm.org/D67192
llvm-svn: 371243
We can rely on X86FixupBWInsts to turn these into MOVZX32. This
simplifies a follow up commit to use MOVSX for i8 sdivrem with
a late optimization to use CBW when register allocation works out.
llvm-svn: 371242
Summary:
We were previously doing it in DAGCombine.
But we also want to do `sub %x, C` -> `add %x, (sub 0, C)` for vectors in DAGCombine.
So if we had `sub %x, -1`, we'll transform it to `add %x, 1`,
which `combineIncDecVector()` will immediately transform back into `sub %x, -1`,
and here we go again...
I've marked this as NFC since not a single test changes,
but since that 'changes' DAGCombine, probably this isn't fully NFC.
Reviewers: RKSimon, craig.topper, spatel
Reviewed By: craig.topper
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D62327
llvm-svn: 370327
LEA doesn't affect flags, so use it more liberally to replace an ADD when
we know that the ADD operands affect flags.
In the motivating example from PR40483:
https://bugs.llvm.org/show_bug.cgi?id=40483
...this lets us avoid duplicating a math op just to avoid flag conflict.
As mentioned in the TODO comments, this heuristic can be extended to
fire more often if that leads to more improvements.
Differential Revision: https://reviews.llvm.org/D64707
llvm-svn: 366431
Summary:
We attempt to prevent folding immediates with multiple users under optsize. But we only do this from store nodes and X86ISD::ADD/SUB/XOR/OR/AND patterns. We don't do it for ISD::ADD/SUB/XOR/OR/AND even though we count them as users when deciding whether to fold into other nodes. This leads to situations where we block folding to a compare for example, but still fold into an AND or OR as seen in PR27202.
Unfortunately touching the isel patterns in tablegen for the ISD::ADD/SUB/XOR/OR/AND opcodes will cause the patterns to be unusable for fast isel. And we don't have a way to make a fast isel only pattern.
To workaround this, this patch adds custom isel in front of the isel table that will select the non-immediate forms if the immediate has additional users. This may create some issues for ANDN and NOT matching. And there's room for improvement with unsigned 32 immediates on 64-bit AND.
This patch needs more thorough test cases, but I wanted to get feedback on the direction. Please send me any other test cases you've seen in the wild.
I think we probably have the same issue with the immediate matching when we fold RMW from X86ISD::ADD/SUB/XOR/OR/AND. And our TEST immedaite shrinking logic. Our cost modeling for immediates that can fit in a sign extended 8-bit immediate on a 16/32/64 bit operation is completely wrong.
I also wonder if we should update the ConstantHoisting cost model and block folding for "opaque" constants. But of course constants can still be created by DAG combine and lowering optimizations.
Fixes PR27202
Reviewers: spatel, RKSimon, andreadb
Reviewed By: RKSimon
Subscribers: jsji, hiraditya, jdoerfert, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D59909
llvm-svn: 365163
Summary:
The one thing of note here is that the 'bitwidth' constant (32/64) was previously pessimistic.
Given `x & (-1 >> (C - z))`, we were taking `C` to be `bitwidth(x)`, but in reality
we want `(-1 >> (C - z))` pattern to mean "low z bits must be all-ones".
And for that, `C` should be `bitwidth(-1 >> (C - z))`, i.e. of the shift operation itself.
Last pattern D does not seem to exhibit any of these truncation issues.
Although it has the opposite problem - if we extract low bits (no shift) from i64,
and then truncate to i32, then we fail to shrink this 64-bit extraction into 32-bit extraction.
Reviewers: RKSimon, craig.topper, spatel
Reviewed By: RKSimon
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D62806
llvm-svn: 364419
Summary:
(Not so) boringly identical to pattern a (D62786)
Not yet sure how do deal with the last pattern c.
Reviewers: RKSimon, craig.topper, spatel
Reviewed By: RKSimon
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D62793
llvm-svn: 364418
Summary:
Finally tying up loose ends here.
The problem is quite simple:
If we have pattern `(x >> start) & (1 << nbits) - 1`,
and then truncate the result, that truncation will be propagated upwards,
into the `and`. And that isn't currently handled.
I'm only fixing pattern `a` here,
the same fix will be needed for patterns `b`/`c` too.
I *think* this isn't missing any extra legality checks,
since we only look past truncations. Similary, i don't think
we can get any other truncation there other than i64->i32.
Reviewers: craig.topper, RKSimon, spatel
Reviewed By: craig.topper
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D62786
llvm-svn: 364417
First step toward addressing the vector-reduce-mul-widen.ll regression in D63281 - we should replace ANY_EXTEND/ANY_EXTEND_VECTOR_INREG in X86ISelDAGToDAG to avoid having to add duplicate patterns when treating any extensions as legal.
In future patches this will also allow us to keep any extension nodes around a lot longer in the DAG, which should mean that we can keep better track of undef elements that otherwise become zeros that we think we have to keep......
Differential Revision: https://reviews.llvm.org/D63326
llvm-svn: 363655
I recently discovered a bug on the x86 platform: The fp80 type was not handled well by x86 for constrained floating point nodes, as their regular counterparts are replaced by extending loads and truncating stores during the preprocess phase. Normally, platforms don't have this issue, as they don't typically attempt to perform such legalizations during instruction selection preprocessing. Before this change, strict_fp nodes survived until they were mutated to normal nodes, which happened shortly after preprocessing on other platforms. This modification lowers these nodes at the same phase while properly utilizing the chain.5
Submitted by: Drew Wock <drew.wock@sas.com>
Reviewed by: Craig Topper, Kevin P. Neal
Approved by: Craig Topper
Differential Revision: https://reviews.llvm.org/D63271
llvm-svn: 363417
Previously we did the equivalent operation in isel patterns with
COPY_TO_REGCLASS operations to transition. By inserting
scalar_to_vetors and extract_vector_elts before isel we can
allow each piece to be selected individually and accomplish the
same final result.
I ideally we'd use vector operations earlier in lowering/combine,
but that looks to be more difficult.
The scalar-fp-to-i64.ll changes are because we have a pattern for
using movlpd for store+extract_vector_elt. While an f64 store
uses movsd. The encoding sizes are the same.
llvm-svn: 362914
We already need to have patterns for X86ISD::RNDSCALE to support software intrinsics. But we currently have 5 sets of patterns for the 5 rounding operations. For of these 6 patterns we have to support 3 vectors widths, 2 element sizes, sse/vex/evex encodings, load folding, and broadcast load folding. This results in a fair amount of bytes in the isel table.
This patch adds code to PreProcessIselDAG to morph the fceil/ffloor/ftrunc/fnearbyint/frint to X86ISD::RNDSCALE. This way we can remove everything, but the intrinsic pattern while still allowing the operations to be considered Legal for DAGCombine and Legalization. This shrinks the DAGISel by somewhere between 9K and 10K.
There is one complication to this, the STRICT versions of these nodes are currently mutated to their none strict equivalents at isel time when the node is visited. This won't be true in the future since that loses the chain ordering information. For now I've also added support for the non-STRICT nodes to Select so we can change the STRICT versions there after they've been mutated to their non-STRICT versions. We'll probably need a STRICT version of RNDSCALE or something to handle this in the future. Which will take us back to needing 2 sets of patterns for strict and non-strict, but that's still better than the 11 or 12 sets of patterns we'd need.
We can probably do something similar for scalar, but I haven't looked at it yet.
Differential Revision: https://reviews.llvm.org/D62757
llvm-svn: 362535
If we're trying to match an LEA, its possible the LEA match will be deemed unprofitable. In which case the negation we created in matchAddress would be left dangling in the SelectionDAG. This could artificially increase use counts for other nodes in the DAG. Though I don't have an example of that. But it just seems like bad form to have dangling nodes in isel.
Differential Revision: https://reviews.llvm.org/D61047
llvm-svn: 360823
The reordering can leave at least a dead TokenFactor in the graph. This cause the linearize scheduler to fail with something like the assert seen in PR22614. This is only one of many ways we can break the linearize scheduler today so I can't say for sure that any of the other failures in that bug were caused by this issue.
This takes the heavy hammer approach of just running RemoveDeadNodes unconditionally at the end of the PreprocessISelDAG. If this turns out to be a compile time hit, we can try to refine it.
Differential Revision: https://reviews.llvm.org/D61164
llvm-svn: 359582
The IndexReg will always be non-null at this point. Earlier in the function, if
IndexReg was null we set it to CurDAG->getRegister(0, VT) which made it
non-null.
llvm-svn: 359170
ReplaceAllUsesWith doesn't remove the node that was replaced. So its left around in the graph messing up use counts on other nodes.
One thing to note, is that this isn't valid if the node being deleted is the root node of an LEA match that gets rejected. In that case the node needs to stay alive because the isel table walking code would still have a reference to it that its going to try to match next. I don't think that's the case here though because the nodes being deleted here should be "and", "srl", and "zero_extend" none of which can be the root node of an LEA match.
Differential Revision: https://reviews.llvm.org/D61048
llvm-svn: 359121
The MOVZX doesn't require an immediate to be encoded at all. Though it does use
a 2 byte opcode so its the same size as a 1 byte immediate. But it has a
separate source and dest register so can help avoid copies.
llvm-svn: 358805
There's one slight regression in here because we don't check that the immediate
already allowed movzx before the shift. I'll fix that next.
llvm-svn: 358804
Summary:
There are two places where we create a HandleSDNode in address matching in order to handle the case where N is changed by CSE. But if we end up not matching, we fall back to code at the bottom of the switch that really would like N to point to something that wasn't CSEd away. So we should make sure we copy the handle back to N on any paths that can reach that code.
This appears to be the true reason we needed to check DELETED_NODE in the negation matching. In pr32329.ll we had two subtracts back to back. We recursed through the first subtract, and onto the second subtract. The second subtract called matchAddressRecursively on its LHS which caused that subtract to CSE. We ultimately failed the match and ended up in the default code. But N was pointing at the old node that had been deleted, but the default code didn't know that and took it as the base register. Then we unwound back to the first subtract and tried to access this bogus base reg requiring the check for deleted node. With this patch we now use the CSE result as the base reg instead.
matchAdd has been broken since sometime in 2015 when it was pulled out of the switch into a helper function. The assignment to N at the end was still there, but N was passed by value and not by reference so the update didn't go anywhere.
Reviewers: niravd, spatel, RKSimon, bkramer
Reviewed By: niravd
Subscribers: llvm-commits, hiraditya
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60843
llvm-svn: 358735
The test file has pairs of tests that are logically equivalent:
https://rise4fun.com/Alive/2zQ
%t4 = and i8 %t1, 8
%t5 = zext i8 %t4 to i16
%sh = shl i16 %t5, 2
%t6 = add i16 %sh, %t0
=>
%t4 = and i8 %t1, 8
%sh2 = shl i8 %t4, 2
%z5 = zext i8 %sh2 to i16
%t6 = add i16 %z5, %t0
...so if we can fold the shift op into LEA in the 1st pattern, then we
should be able to do the same in the 2nd pattern (unnecessary 'movzbl'
is a separate bug I think).
We don't want to do this any sooner though because that would conflict
with generic transforms that try to narrow the width of the shift.
Differential Revision: https://reviews.llvm.org/D60789
llvm-svn: 358622
We had many tablegen patterns for these instructions. And due to the
commutability of the patterns, tablegen expands them to even more patterns. All
together VPTESTMD patterns accounted for more the 50K of the 610K isel table.
This had gotten bad when we stopped canonicalizing AND to vXi64. This required
a pattern for every combination of bitcast input type.
This change moves the matching to custom code where it is easier to look through
the bitcasts without being concerned with the specific types.
The test changes are because we are now stricter with one use checks as its
required to make load folding legal. We now require the AND and any BITCAST to
only have a single use. This prevents forming VPTESTM and a VPAND with the same
inputs.
We now support broadcast loads for 128/256 patterns without VLX. We'll widen to
512-bit like and still fold the broadcast since the amount of memory read
doesn't change.
There are a few tests that got slightly longer because are now prefering
load + VPTESTM over XOR+VPCMPEQ for (seteq (load), allzeros). Previously we were
able to share the XOR with multiple VPTESTM instructions.
llvm-svn: 358359
Summary:
The Linux kernel uses PC-relative mode, so allow that when the code model is
"kernel".
Reviewers: craig.topper
Reviewed By: craig.topper
Subscribers: llvm-commits, kees, nickdesaulniers
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60643
llvm-svn: 358343
We know all our values are limited to 64 bits here so we don't need an APInt.
This should save some generated code checking between large and small size.
llvm-svn: 358338
foldMaskedShiftToScaledMask tries to reorder and & shl to enable the shl to fold into an LEA. But if there is an any_extend between them it doesn't work.
This patch modifies the code to look through any_extend from i32 to i64 when the and mask only uses bits that weren't from the extended part.
This will prevent a regression from D60358 caused by 64-bit SHL being narrowed to 32-bits when their upper bits aren't demanded.
Differential Revision: https://reviews.llvm.org/D60532
llvm-svn: 358139
These ifs were ensuring we don't have to handle types larger than 64 bits probably because we use getZExtValue in several places below them.
None of the callers of this code pass types larger than 64-bits so we can just assert instead of branching in release code.
I've also moved them earlier since we're just looking through operations that don't effect bit width.
This is prep work for some refactoring I plan to do to the (and (shl)) handling code.
llvm-svn: 358123
This function reorders AND and SHL to enable the SHL to fold into an LEA. The
upper bits of the AND will be shifted out by the SHL so it doesn't matter what
mask value we use for these bits. By using sign bits from the original mask in
these upper bits we might enable a shorter immediate encoding to be used.
llvm-svn: 357846
Summary:
This avoids needing an isel pattern for each condition code. And it removes translation switches for converting between Jcc instructions and condition codes.
Now the printer, encoder and disassembler take care of converting the immediate. We use InstAliases to handle the assembly matching. But we print using the asm string in the instruction definition. The instruction itself is marked IsCodeGenOnly=1 to hide it from the assembly parser.
Reviewers: spatel, lebedev.ri, courbet, gchatelet, RKSimon
Reviewed By: RKSimon
Subscribers: MatzeB, qcolombet, eraman, hiraditya, arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60228
llvm-svn: 357802
Summary:
This avoids needing an isel pattern for each condition code. And it removes translation switches for converting between SETcc instructions and condition codes.
Now the printer, encoder and disassembler take care of converting the immediate. We use InstAliases to handle the assembly matching. But we print using the asm string in the instruction definition. The instruction itself is marked IsCodeGenOnly=1 to hide it from the assembly parser.
Reviewers: andreadb, courbet, RKSimon, spatel, lebedev.ri
Reviewed By: andreadb
Subscribers: hiraditya, lebedev.ri, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60138
llvm-svn: 357801
Summary:
Reorder the condition code enum to match their encodings. Move it to MC layer so it can be used by the scheduler models.
This avoids needing an isel pattern for each condition code. And it removes
translation switches for converting between CMOV instructions and condition
codes.
Now the printer, encoder and disassembler take care of converting the immediate.
We use InstAliases to handle the assembly matching. But we print using the
asm string in the instruction definition. The instruction itself is marked
IsCodeGenOnly=1 to hide it from the assembly parser.
This does complicate the scheduler models a little since we can't assign the
A and BE instructions to a separate class now.
I plan to make similar changes for SETcc and Jcc.
Reviewers: RKSimon, spatel, lebedev.ri, andreadb, courbet
Reviewed By: RKSimon
Subscribers: gchatelet, hiraditya, kristina, lebedev.ri, jdoerfert, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D60041
llvm-svn: 357800
SUBREG_TO_REG is supposed to be used to assert that we know the upper bits are
zero. But that isn't the case here. We've done no analysis of the inputs.
llvm-svn: 357673
This custom inserter existed so we could do a weird thing where we pretended that the instructions support
a full address mode instead of taking a pointer in EAX/RAX. I think was largely so we could be pointer
size agnostic in the isel pattern.
To make this work we would then put the address into an LEA into EAX/RAX in front of the instruction after
isel. But the LEA is overkill when we just have a base pointer. So we end up using the LEA as a slower MOV
instruction.
With this change we now just do custom selection during isel instead and just assign the incoming address
of the intrinsic into EAX/RAX based on its size. After the intrinsic is selected, we can let isel take
care of selecting an LEA or other operation to do any address computation needed in this basic block.
I've also split the instruction into a 32-bit mode version and a 64-bit mode version so the implicit
use is properly sized based on the pointer. Without this we get comments in the assembly output about
killing eax and defing rax or vice versa depending on whether we define the instruction to use EAX/RAX.
llvm-svn: 357652
Negate updates flags like a subtract. We should be able to use the flags from the RMW form of negate when we have (store (X86ISD::SUB 0, load A), A)
Differential Revision: https://reviews.llvm.org/D60007
llvm-svn: 357353
For 64-bit operations we should consider if the immediate can be made to fit
in an unsigned 32-bits immedate. For OR/XOR this allows us to load the immediate
with MOV32ri instead of movabsq. For AND this allows us to fold the immediate.
Differential Revision: https://reviews.llvm.org/D59867
llvm-svn: 357196
This makes more sense as a place to initialize these. I don't think runOnMachineFunction was overriden when these cached values were originally created.
llvm-svn: 357123
Previously we manually selected the AND/OR/XOR with immediate and the SHL(or ADD if the shift is 1). But this was missing out on the opportunity to use a 64 bit AND with a 32-bit immediate and possibly other isel tricks we have built into the tables.
Instead, insert the new nodes into the DAG using insertDAGNode and allow them each to be selected through the normal table.
llvm-svn: 357049
We were manually outputting the code we would get from selecting ANY_EXTEND. We
can save some code by just letting an ANY_EXTEND go through isel on its own.
llvm-svn: 357045
We were using OrigNBits, but that put all the nodes before the node we used to start the control computation. This caused some node earlier than the sequence we inserted to be selected before the sequence we created. We want our new sequence to be selected first since it depends on OrigNBits.
I don't have a test case. Found by reviewing the code.
llvm-svn: 356979
Normally when the nodes we use here(AND32ri8 for example) are selected their
immediates are just converted from ConstantSDNode to TargetConstantSDNode
without changing VT from the original operation VT. So we should still be
emitting them with the operation VT.
Theoretically this could expose more accurate opportunities for CSE.
llvm-svn: 356869
128 won't fit in a sign extended 8-bit immediate, but we can negate it to -128 and use the other operation. This results in a shorter encoding since the move would have used 16 or 32 bits for the immediate.
llvm-svn: 355484
These allows use to use the same set of isel patterns for sra/srl/shl which are undefined for out of range shifts and intrinsic shifts which aren't undefined.
Doing this late allows DAG combine to have every opportunity to optimize the sra/srl/shl nodes.
This removes about 7000 bytes from the isel table and simplies the td files.
llvm-svn: 355071
If the LHS has known zeros, the RHS immediate will have had bits removed. So call computeKnownBits to get the known zeroes so we can handle this case.
Differential Revision: https://reviews.llvm.org/D58475
llvm-svn: 354811
Summary:
Noticed while looking at D56052.
```
// The 'control' of BEXTR has the pattern of:
// [15...8 bit][ 7...0 bit] location
// [ bit count][ shift] name
// I.e. 0b000000011'00000001 means (x >> 0b1) & 0b11
```
I.e. we do not care about any of the bits aside from the low 16 bits.
So there is no point in doing the `slh`,`or` in 64 bits,
let's just do everything in 32 bits, and anyext if needed.
We could do that in 16 even, but we intentionally don't
zext to i16 (longer encoding IIRC),
so i'm guessing the same applies here.
Reviewers: craig.topper, andreadb, RKSimon
Reviewed By: craig.topper
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D56715
llvm-svn: 353073
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
This cleans up the duplication we have with both intrinsic isel patterns and vselect isel patterns. This should also allow the intrinsics to get SimplifyDemandedBits support for the condition.
I've switched the canonical pattern in isel to use the X86ISD::BLENDV node instead of VSELECT. Since it always seemed weird to move from BLENDV with its relaxed rules on condition bits to VSELECT which has strict rules about all bits of the condition element being the same. Its more correct to go from VSELECT to BLENDV.
Differential Revision: https://reviews.llvm.org/D56771
llvm-svn: 351380
That's really what it is. If we didn't use intrinsics for BLENDVPS/BLENDVPD/PBLENDVB all the way to isel, this is the node we would use.
llvm-svn: 351278
Doing this late so we will prefer to fold the AND into a masked comparison first. That can be better for the live range of the mask register.
Differential Revision: https://reviews.llvm.org/D56246
llvm-svn: 350374
INC/DEC are pretty much the same as ADD/SUB except that they don't update the C flag.
This patch removes the special nodes and just pattern matches from ADD/SUB during isel if the C flag isn't being used.
I had to avoid selecting DEC is the result isn't used. This will become a SUB immediate which will turned into a CMP later by optimizeCompareInstr. This lead to the one test change where we use a CMP instead of a DEC for an overflow intrinsic since we only checked the flag.
This also exposed a hole in our RMW flag matching use of hasNoCarryFlagUses. Our root node for the match is a store and there's no guarantee that all the flag users have been selected yet. So hasNoCarryFlagUses needs to check copyToReg and machine opcodes, but it also needs to check for the pre-match SETCC, SETCC_CARRY, BRCOND, and CMOV opcodes.
Differential Revision: https://reviews.llvm.org/D55975
llvm-svn: 350245
All of these use custom isel so we can pretty easily detect the differences in the custom code in X86ISelDAGToDAG. The ISD opcodes just need to express the desired semantics not the details of how they would be selected by isel. So unifying them lets us remove the special casing from lowering.
llvm-svn: 350206
Remove the TESTmr isel patterns and add another postprocessing combine for TESTrr+ANDrm->TESTmr. We already have a postprocessing combine for TESTrr+ANDrr->TESTrr. With this we can give ANDN a chance to match first. And clean it up during post processing if we ended up with just a regular AND.
This is another step towards my plan to gut EmitTest and do more flag handling during isel matching or by using optimizeCompare.
llvm-svn: 350038
This fixes the patterns that have or/and as a root. 'and' is handled differently since thy usually have a CMP wrapped around them.
I had to look for uses of the CF flag because all these nodes have non-standard CF flag behavior. A real or/xor would always clear CF. In practice we shouldn't be using the CF flag from these nodes as far as I know.
Differential Revision: https://reviews.llvm.org/D55813
llvm-svn: 349962
This shortens the switches in X86ISelDAGToDAG.cpp to only need to check condition code instead of a list of opcodes.
This also fixes a bug where the memory forms of SETcc were missing from hasNoCarryFlagUses.
llvm-svn: 349868
The (cmp (and X, Y) 0) pattern is greedy and ends up forming a TESTrr and consuming the and when it might be better to use one of the BMI/TBM like BLSR or BLSI.
This patch moves removes the pattern from isel and adds a post processing check to combine TESTrr+ANDrr into just a TESTrr. With this patch we are able to select the BMI/TBM instructions, but we'll also emit a TESTrr when the result is compared to 0. In many cases the peephole pass will be able to use optimizeCompareInstr to remove the TEST, but its probably not perfect.
Differential Revision: https://reviews.llvm.org/D55870
llvm-svn: 349661
The only caller of this turns CMP with 0 into TEST. CMP with 0 and TEST both set OF to 0 so we should have no issues with instructions that only use OF.
Though I don't think there's any reason we would read just OF after a compare with 0 anyway. So this probably isn't an observable change.
llvm-svn: 349223
hasNoCarryFlagUses hardcoded that the flag result is 1 and used that to filter which uses were of interest. hasNoSignedComparisonUses just assumes the only result is flags and checks whether any user of the node is a CopyToReg instruction.
After this patch we now do a result number check in both and rely on the caller to provide the result number.
This shouldn't change behavior it was just an odd difference between the two functions that I noticed.
llvm-svn: 349222
MULX has somewhat improved register allocation constraints compared to the legacy MUL instruction. Both output registers are encoded instead of fixed to EAX/EDX, but EDX is used as input. It also doesn't touch flags. Unfortunately, the encoding is longer.
Prefering it whenever BMI2 is enabled is probably not optimal. Choosing it should somehow be a function of register allocation constraints like converting adds to three address. gcc and icc definitely don't pick MULX by default. Not sure what if any rules they have for using it.
Differential Revision: https://reviews.llvm.org/D55565
llvm-svn: 348975
Summary:
As discussed in previous review, and noted in the FIXME, if `X` is actually an `lshr Y, Z` (logical!),
we can fold the `Z` into 'control`, and let the `BEXTR` do this too.
We could just insert those 8 bits of shift amount into control,
but it is better to instead zero-extend them, and 'or' them in place.
We can only do this for `lshr`, not `ashr`, because we do not know that the mask cover only the bits of `Y`,
and not any of the sign-extended bits.
The obvious question is, is this actually legal to do?
I believe it is. Relevant quotes, from `Intel® 64 and IA-32 Architectures Software Developer’s Manual`, `BEXTR — Bit Field Extract`:
* `Bit 7:0 of the second source operand specifies the starting bit position of bit extraction.`
* `A START value exceeding the operand size will not extract any bits from the second source operand.`
* `Only bit positions up to (OperandSize -1) of the first source operand are extracted.`
* `All higher order bits in the destination operand (starting at bit position LENGTH) are zeroed.`
* `The destination register is cleared if no bits are extracted.`
FIXME: if we can do this, i wonder if we should prefer `BEXTR` over `BZHI` in such cases.
Reviewers: RKSimon, craig.topper, spatel, andreadb
Reviewed By: RKSimon, craig.topper, andreadb
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D54095
llvm-svn: 347048
Summary:
The final pattern.
There is no test changes:
* We are looking for the pattern with one-use of it's mask,
* If the mask is one-use, D48768 will unfold it into pattern d.
* Thus, the tests have extra-use on the mask.
* Thus, only the BMI2 BZHI can be tested, and it already worked.
* So there is no BMI1 test coverage, we just assume it works since it uses the same codepath.
Reviewers: craig.topper, RKSimon
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D53575
llvm-svn: 345584
This patch brings back the MOV64r0 pseudo instruction for zeroing a 64-bit register. This replaces the SUBREG_TO_REG MOV32r0 sequence we use today. Post register allocation we will rewrite the MOV64r0 to a 32-bit xor with an implicit def of the 64-bit register similar to what we do for the various XMM/YMM/ZMM zeroing pseudos.
My main motivation is to enable the spill optimization in foldMemoryOperandImpl. As we were seeing some code that repeatedly did "xor eax, eax; store eax;" to spill several registers with a new xor for each store. With this optimization enabled we get a store of a 0 immediate instead of an xor. Though I admit the ideal solution would be one xor where there are multiple spills. I don't believe we have a test case that shows this optimization in here. I'll see if I can try to reduce one from the code were looking at.
There's definitely some other machine CSE(and maybe other passes) behavior changes exposed by this patch. So it seems like there might be some other deficiencies in SUBREG_TO_REG handling.
Differential Revision: https://reviews.llvm.org/D52757
llvm-svn: 345165
This initially landed in rL345014, but was reverted in rL345017
due to sanitizer-x86_64-linux-fast buildbot failure in
check-lld (ELF/relocatable-versioned.s) test.
While i'm not yet quite sure what is the problem, one obvious
thing here is that extra truncation roundtrip.
Maybe that's it? If not, will re-revert.
Differential Revision: https://reviews.llvm.org/D53521
llvm-svn: 345027
Summary:
Continuation of D52348.
We also get the `c) x & (-1 >> (32 - y))` pattern here, because of the D48768.
I will add extra-uses into those tests and follow-up with a patch to handle those patterns too.
Reviewers: RKSimon, craig.topper
Reviewed By: craig.topper
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D53521
llvm-svn: 345014
I've included a fix to DAGCombiner::ForwardStoreValueToDirectLoad that I believe will prevent the previous miscompile.
Original commit message:
Theoretically this was done to simplify the amount of isel patterns that were needed. But it also meant a substantial number of our isel patterns have to match an explicit bitcast. By making the vXi32/vXi16/vXi8 types legal for loads, DAG combiner should be able to change the load type to rem
I had to add some additional plain load instruction patterns and a few other special cases, but overall the isel table has reduced in size by ~12000 bytes. So it looks like this promotion was hurting us more than helping.
I still have one crash in vector-trunc.ll that I'm hoping @RKSimon can help with. It seems to relate to using getTargetConstantFromNode on a load that was shrunk due to an extract_subvector combine after the constant pool entry was created. So we end up decoding more mask elements than the lo
I'm hoping this patch will simplify the number of patterns needed to remove the and/or/xor promotion.
Reviewers: RKSimon, spatel
Reviewed By: RKSimon
Subscribers: llvm-commits, RKSimon
Differential Revision: https://reviews.llvm.org/D53306
llvm-svn: 344965
Summary:
As discussed in D52304 / IRC, we now have pattern matching for
'bit extract' in two places - tablegen and `X86DAGToDAGISel`.
There are 4 patterns.
And we will have a problem with `x & (-1 >> (32 - y))` pattern.
* If the mask is one-use, then it is always unfolded into `x << (32 - y) >> (32 - y)` first.
Thus, the existing test coverage is already broken.
* If it is not one-use, then it is not unfolded, and is matched as BZHI.
* If it is not one-use, we will not match it as BEXTR. And if it is one-use, it will have been unfolded already.
So we will either not handle that pattern for BEXTR, or not have test coverage for it.
This is bad.
As discussed with @craig.topper, let's unify this matching, and do everything in `X86DAGToDAGISel`.
Then we will not have code duplication, and will have proper test coverage.
This indeed does not affect any tests, and this is great.
It means that for these two patterns, the `X86DAGToDAGISel` is identical to the tablegen version.
Please review carefully, i'm not fully sure about that intrinsic change, and introduction of the new `X86ISD` opcode.
Reviewers: craig.topper, RKSimon, spatel
Reviewed By: craig.topper
Subscribers: llvm-commits, craig.topper
Differential Revision: https://reviews.llvm.org/D53164
llvm-svn: 344904
Summary:
Trivial continuation of D52304.
While this pattern is not canonical, we do select it in the BZHI case,
so this should not be any different.
Reviewers: RKSimon, craig.topper, spatel
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D52348
llvm-svn: 344902
Summary:
Theoretically this was done to simplify the amount of isel patterns that were needed. But it also meant a substantial number of our isel patterns have to match an explicit bitcast. By making the vXi32/vXi16/vXi8 types legal for loads, DAG combiner should be able to change the load type to remove the bitcast.
I had to add some additional plain load instruction patterns and a few other special cases, but overall the isel table has reduced in size by ~12000 bytes. So it looks like this promotion was hurting us more than helping.
I still have one crash in vector-trunc.ll that I'm hoping @RKSimon can help with. It seems to relate to using getTargetConstantFromNode on a load that was shrunk due to an extract_subvector combine after the constant pool entry was created. So we end up decoding more mask elements than the load size.
I'm hoping this patch will simplify the number of patterns needed to remove the and/or/xor promotion.
Reviewers: RKSimon, spatel
Reviewed By: RKSimon
Subscribers: llvm-commits, RKSimon
Differential Revision: https://reviews.llvm.org/D53306
llvm-svn: 344877
Summary:
These nodes exist to overcome an isel problem where we can generate a zero extend of an AH register followed by an extract subreg, and another zero extend. The first zero extend exists to avoid a partial register update copying the AH register into the low 8-bits. The second zero extend exists if the user wanted the remainder zero extended.
To make this work we had a DAG combine to morph the DIVREM opcode to a special opcode that included the extend. But then we had to add the new node to computeKnownBits and computeNumSignBits to process the extension portion.
This patch instead removes all of that and adds a late peephole to detect the two extends.
Reviewers: RKSimon, spatel
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D53449
llvm-svn: 344874
There is no guarantee the root is at the end if isel created any nodes without morphing them. This includes the nodes created by manual isel from C++ code in X86ISelDAGToDAG.
This is similar to r333415 from PowerPC which is where I originally stole the peephole loop from.
I don't have a test case, but without this a future patch doesn't work which is how I found it.
llvm-svn: 344808
Allows to disable direct TLS segment access (%fs or %gs). GCC supports
a similar flag, it can be useful in some circumstances, e.g. when a thread
context block needs to be updated directly from user space. More info
and specific use cases: https://bugs.llvm.org/show_bug.cgi?id=16145
There is another revision for clang as well.
Related: D53102
All X86 CodeGen tests appear to pass:
```
[46/47] Running lit suite /SourceCache/llvm-trunk-8.0/test/CodeGen
Testing Time: 23.17s
Expected Passes : 3801
Expected Failures : 15
Unsupported Tests : 8021
```
Reviewed by: Craig Topper.
Patch by nruslan (Ruslan Nikolaev).
Differential Revision: https://reviews.llvm.org/D53103
llvm-svn: 344723
Without this we match the CMP+AND to a TEST and then match the SHR separately. I'm trusting analyzeCompare to remove the TEST during the peephole pass. Otherwise we need to check the flag users to see if they only use the Z flag.
This recovers a case lost by r344270.
Differential Revision: https://reviews.llvm.org/D53310
llvm-svn: 344649
This is an alternative to D53080 since I think using a BEXTR for a shifted mask is definitely an improvement when the shl can be absorbed into addressing mode. The other cases I'm less sure about.
We already have several tricks for handling an and of a shift in address matching. This adds a new case for BEXTR.
I've moved the BEXTR matching code back to X86ISelDAGToDAG to allow it to match. I suppose alternatively we could directly emit a X86ISD::BEXTR node that isel could pattern match. But I'm trying to view BEXTR matching as an isel concern so DAG combine can see 'and' and 'shift' operations that are well understood. We did lose a couple cases from tbm_patterns.ll, but I think there are ways to recover that.
I've also put back the manual load folding code in matchBEXTRFromAnd that I removed a few months ago in r324939. This gives us some more freedom to make decisions based on the ability to fold a load. I haven't done anything with that yet.
Differential Revision: https://reviews.llvm.org/D53126
llvm-svn: 344270
Summary:
As discussed in D48491, we can't really do this in the TableGen,
since we need to produce *two* instructions. This only implements
one single pattern. The other 3 patterns will be in follow-ups.
I'm not sure yet if we want to also fuse shift into here
(i.e `(x >> start) & ...`)
Reviewers: RKSimon, craig.topper, spatel
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D52304
llvm-svn: 344224
Remove tryFoldVecLoad since tryFoldLoad would call IsProfitableToFold and pick up the new check.
This saves about 5K out of ~600K on the generated isel table.
llvm-svn: 344189
Summary:
As discussed in [[ https://bugs.llvm.org/show_bug.cgi?id=38938 | PR38938 ]],
we fail to emit `BEXTR` if the mask is shifted.
We can't deal with that in `X86DAGToDAGISel` `before the address mode for the inc is selected`,
and we can't really do it in the normal DAGCombine, because we don't have generic `ISD::BitFieldExtract` node,
and if we simply turn the shifted mask into a normal mask + shift-left, it will be folded back.
So it would seem X86ISelLowering is the place to handle this.
This patch only moves the matchBEXTRFromAnd()
from X86DAGToDAGISel to X86ISelLowering.
It does not add support for the 'shifted mask' pattern.
Reviewers: RKSimon, craig.topper, spatel
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D52426
llvm-svn: 344179
This includes a fix to prevent i16 compares with i32/i64 ands from being shrunk if bit 15 of the and is set and the sign bit is used.
Original commit message:
Currently we skip looking through truncates if the sign flag is used. But that's overly restrictive.
It's safe to look through the truncate as long as we ensure one of the 3 things when we shrink. Either the MSB of the mask at the shrunken size isn't set. If the mask bit is set then either the shrunk size needs to be equal to the compare size or the sign
There are still missed opportunities to shrink a load and fold it in here. This will be fixed in a future patch.
llvm-svn: 343539
There's a subtle bug in the handling of truncate from i32/i64 to i32 without minsize.
I'll be adding more test cases and trying to find a fix.
llvm-svn: 343516
This patch adds load folding support to the test shrinking code. This was noticed missing in the review for D52669
Differential Revision: https://reviews.llvm.org/D52699
llvm-svn: 343499
Currently we skip looking through truncates if the sign flag is used. But that's overly restrictive.
It's safe to look through the truncate as long as we ensure one of the 3 things when we shrink. Either the MSB of the mask at the shrunken size isn't set. If the mask bit is set then either the shrunk size needs to be equal to the compare size or the sign flag needs to be unused.
There are still missed opportunities to shrink a load and fold it in here. This will be fixed in a future patch.
Differential Revision: https://reviews.llvm.org/D52669
llvm-svn: 343498
Summary:
This function turns (X >> C1) & C2 into a BMI BEXTR or TBM BEXTRI instruction. For BMI BEXTR we have to materialize an immediate into a register to feed to the BEXTR instruction.
The BMI BEXTR instruction is 2 uops on Intel CPUs. It looks like on SKL its one port 0/6 uop and one port 1/5 uop. Despite what Agner's tables say. I know one of the uops is a regular shift uop so it would have to go through the port 0/6 shifter unit. So that's the same or worse execution wise than the shift+and which is one 0/6 uop and one 0/1/5/6 uop. The move immediate into register is an additional 0/1/5/6 uop.
For now I've limited this transform to AMD CPUs which have a single uop BEXTR. If may also might make sense if we can fold a load or if the and immediate is larger than 32-bits and can't be encoded as a sign extended 32-bit value or if LICM or CSE can hoist the move immediate and share it. But we'd need to look more carefully at that. In the regression I looked at it doesn't look load folding or large immediates were occurring so the regression isn't caused by the loss of those. So we could try to be smarter here if we find a compelling case.
Reviewers: RKSimon, spatel, lebedev.ri, andreadb
Reviewed By: RKSimon
Subscribers: llvm-commits, andreadb, RKSimon
Differential Revision: https://reviews.llvm.org/D52570
llvm-svn: 343399
Previously we only handled loads in operand 0, but nothing guarantees the load will be operand 0 for commutable operations.
Differential Revision: https://reviews.llvm.org/D51768
llvm-svn: 341675
The peephole pass likely gets this normally, but we should be doing it during isel.
Ideally we'd just make the X86adc_flag pattern SDNPCommutable, but the tablegen doesn't handle that when one of the operands is a register reference.
llvm-svn: 341596
The commit that added this functionality:
rL322957
may be causing/exposing a miscompile in PR38648:
https://bugs.llvm.org/show_bug.cgi?id=38648
so allow enabling/disabling to make debugging easier.
llvm-svn: 340540
subtarget features for indirect calls and indirect branches.
This is in preparation for enabling *only* the call retpolines when
using speculative load hardening.
I've continued to use subtarget features for now as they continue to
seem the best fit given the lack of other retpoline like constructs so
far.
The LLVM side is pretty simple. I'd like to eventually get rid of the
old feature, but not sure what backwards compatibility issues that will
cause.
This does remove the "implies" from requesting an external thunk. This
always seemed somewhat questionable and is now clearly not desirable --
you specify a thunk the same way no matter which set of things are
getting retpolines.
I really want to keep this nicely isolated from end users and just an
LLVM implementation detail, so I've moved the `-mretpoline` flag in
Clang to no longer rely on a specific subtarget feature by that name and
instead to be directly handled. In some ways this is simpler, but in
order to preserve existing behavior I've had to add some fallback code
so that users who relied on merely passing -mretpoline-external-thunk
continue to get the same behavior. We should eventually remove this
I suspect (we have never tested that it works!) but I've not done that
in this patch.
Differential Revision: https://reviews.llvm.org/D51150
llvm-svn: 340515
Inspired by what AArch64 does for shifts, this patch attempts to replace shift amounts with neg if we can.
This is done directly as part of isel so its as late as possible to avoid breaking some BZHI patterns since those patterns need an unmasked (32-n) to be correct.
To avoid manual load folding and custom instruction selection for the negate. I've inserted new nodes in the DAG above the shift node in topological order.
Differential Revision: https://reviews.llvm.org/D48789
llvm-svn: 340441
`MachineMemOperand` pointers attached to `MachineSDNodes` and instead
have the `SelectionDAG` fully manage the memory for this array.
Prior to this change, the memory management was deeply confusing here --
The way the MI was built relied on the `SelectionDAG` allocating memory
for these arrays of pointers using the `MachineFunction`'s allocator so
that the raw pointer to the array could be blindly copied into an
eventual `MachineInstr`. This creates a hard coupling between how
`MachineInstr`s allocate their array of `MachineMemOperand` pointers and
how the `MachineSDNode` does.
This change is motivated in large part by a change I am making to how
`MachineFunction` allocates these pointers, but it seems like a layering
improvement as well.
This would run the risk of increasing allocations overall, but I've
implemented an optimization that should avoid that by storing a single
`MachineMemOperand` pointer directly instead of allocating anything.
This is expected to be a net win because the vast majority of uses of
these only need a single pointer.
As a side-effect, this makes the API for updating a `MachineSDNode` and
a `MachineInstr` reasonably different which seems nice to avoid
unexpected coupling of these two layers. We can map between them, but we
shouldn't be *surprised* at where that occurs. =]
Differential Revision: https://reviews.llvm.org/D50680
llvm-svn: 339740
There are a lot of permutations of types here generating a lot of patterns in the isel table. It's more efficient to just ReplaceUses and RemoveDeadNode from the Select function.
The test changes are because we have a some shuffle patterns that have a bitcast as their root node. But the behavior is identical to another instruction whose pattern doesn't start with a bitcast. So this isn't a functional change.
llvm-svn: 338824
If the producing instruction is legacy encoded it doesn't implicitly zero the upper bits. This is important for the SHA instructions which don't have a VEX encoded version. We might also be able to hit this with the incomplete f128 support that hasn't been ported to VEX.
llvm-svn: 338812
Don't try to generate large PIC code for non-ELF targets. Neither COFF
nor MachO have relocations for large position independent code, and
users have been using "large PIC" code models to JIT 64-bit code for a
while now. With this change, if they are generating ELF code, their
JITed code will truly be PIC, but if they target MachO or COFF, it will
contain 64-bit immediates that directly reference external symbols. For
a JIT, that's perfectly fine.
llvm-svn: 337740
We were accidentally connecting it to result 0 instead of result 1. This was caught by the machine verifier that noticed the flags were dead, but we were using them somehow. I'm still not clear what actually happened downstream.
llvm-svn: 336925
We can instead block the load folding isProfitableToFold. Then isel will emit a register->register move for the zeroing part and a separate load. The PostProcessISelDAG should be able to remove the register->register move.
This saves us patterns and fixes the fact that we only had unaligned load patterns. The test changes show places where we should have been using an aligned load.
llvm-svn: 336828
This is a follow up to r335753. At the time I forgot about isProfitableToFold which makes this pretty easy.
Differential Revision: https://reviews.llvm.org/D48706
llvm-svn: 335895
Reverting because this is causing failures in the LLDB test suite on
GreenDragon.
LLVM ERROR: unsupported relocation with subtraction expression, symbol
'__GLOBAL_OFFSET_TABLE_' can not be undefined in a subtraction
expression
llvm-svn: 335894
BMI2 added new shift by register instructions that have the ability to fold a load.
Normally without doing anything special isel would prefer folding a load over folding an immediate because the load folding pattern has higher "complexity". This would require an instruction to move the immediate into a register. We would rather fold the immediate instead and have a separate instruction for the load.
We used to enforce this priority by artificially lowering the complexity of the load pattern.
This patch changes this to instead reject the load fold in isProfitableToFoldLoad if there is an immediate. This is more consistent with other binops and feels less hacky.
llvm-svn: 335804
If we turn X86ISD::AND into ISD::AND, we delete N. But we were continuing onto the next block of code even though N no longer existed.
Just happened to notice it. I assume asan didn't notice it because we explicitly unpoison deleted nodes and give them a DELETE_NODE opcode.
llvm-svn: 335787
The large code model allows code and data segments to exceed 2GB, which
means that some symbol references may require a displacement that cannot
be encoded as a displacement from RIP. The large PIC model even relaxes
the assumption that the GOT itself is within 2GB of all code. Therefore,
we need a special code sequence to materialize it:
.LtmpN:
leaq .LtmpN(%rip), %rbx
movabsq $_GLOBAL_OFFSET_TABLE_-.LtmpN, %rax # Scratch
addq %rax, %rbx # GOT base reg
From that, non-local references go through the GOT base register instead
of being PC-relative loads. Local references typically use GOTOFF
symbols, like this:
movq extern_gv@GOT(%rbx), %rax
movq local_gv@GOTOFF(%rbx), %rax
All calls end up being indirect:
movabsq $local_fn@GOTOFF, %rax
addq %rbx, %rax
callq *%rax
The medium code model retains the assumption that the code segment is
less than 2GB, so calls are once again direct, and the RIP-relative
loads can be used to access the GOT. Materializing the GOT is easy:
leaq _GLOBAL_OFFSET_TABLE_(%rip), %rbx # GOT base reg
DSO local data accesses will use it:
movq local_gv@GOTOFF(%rbx), %rax
Non-local data accesses will use RIP-relative addressing, which means we
may not always need to materialize the GOT base:
movq extern_gv@GOTPCREL(%rip), %rax
Direct calls are basically the same as they are in the small code model:
They use direct, PC-relative addressing, and the PLT is used for calls
to non-local functions.
This patch adds reasonably comprehensive testing of LEA, but there are
lots of interesting folding opportunities that are unimplemented.
I restricted the MCJIT/eh-lg-pic.ll test to Linux, since the large PIC
code model is not implemented for MachO yet.
Differential Revision: https://reviews.llvm.org/D47211
llvm-svn: 335508
Summary:
The large code model allows code and data segments to exceed 2GB, which
means that some symbol references may require a displacement that cannot
be encoded as a displacement from RIP. The large PIC model even relaxes
the assumption that the GOT itself is within 2GB of all code. Therefore,
we need a special code sequence to materialize it:
.LtmpN:
leaq .LtmpN(%rip), %rbx
movabsq $_GLOBAL_OFFSET_TABLE_-.LtmpN, %rax # Scratch
addq %rax, %rbx # GOT base reg
From that, non-local references go through the GOT base register instead
of being PC-relative loads. Local references typically use GOTOFF
symbols, like this:
movq extern_gv@GOT(%rbx), %rax
movq local_gv@GOTOFF(%rbx), %rax
All calls end up being indirect:
movabsq $local_fn@GOTOFF, %rax
addq %rbx, %rax
callq *%rax
The medium code model retains the assumption that the code segment is
less than 2GB, so calls are once again direct, and the RIP-relative
loads can be used to access the GOT. Materializing the GOT is easy:
leaq _GLOBAL_OFFSET_TABLE_(%rip), %rbx # GOT base reg
DSO local data accesses will use it:
movq local_gv@GOTOFF(%rbx), %rax
Non-local data accesses will use RIP-relative addressing, which means we
may not always need to materialize the GOT base:
movq extern_gv@GOTPCREL(%rip), %rax
Direct calls are basically the same as they are in the small code model:
They use direct, PC-relative addressing, and the PLT is used for calls
to non-local functions.
This patch adds reasonably comprehensive testing of LEA, but there are
lots of interesting folding opportunities that are unimplemented.
Reviewers: chandlerc, echristo
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D47211
llvm-svn: 335297
I don't believe there is any real reason to have separate X86 specific opcodes for vector compares. Setcc has the same behavior just uses a different encoding for the condition code.
I had to change the CondCodeAction for SETLT and SETLE to prevent some transforms from changing SETGT lowering.
Differential Revision: https://reviews.llvm.org/D43608
llvm-svn: 335173
Some of the calls to hasSingleUseFromRoot were passing the load itself. If the load's chain result has a user this would count against that. By getting the true parent of the match and ensuring any intermediate between the match and the load have a single use we can avoid this case. isLegalToFold will take care of checking users of the load's data output.
This fixed at least fma-scalar-memfold.ll to succed without the peephole pass.
llvm-svn: 334908
All of the cases are already wrapped in curly braces so declaring a variable there isn't an issue. And the variables aren't assigned or used in the larger scope.
llvm-svn: 334436
Only the bottom 16-bits of BEXTR's control op are required (0:8 INDEX, 15:8 LENGTH).
Differential Revision: https://reviews.llvm.org/D47690
llvm-svn: 334083
This code should really do exactly the same thing for 32-bit x86 and
64-bit small code models, with the exception that RIP-relative
addressing can't use base and index registers.
llvm-svn: 332893
The DEBUG() macro is very generic so it might clash with other projects.
The renaming was done as follows:
- git grep -l 'DEBUG' | xargs sed -i 's/\bDEBUG\s\?(/LLVM_DEBUG(/g'
- git diff -U0 master | ../clang/tools/clang-format/clang-format-diff.py -i -p1 -style LLVM
- Manual change to APInt
- Manually chage DOCS as regex doesn't match it.
In the transition period the DEBUG() macro is still present and aliased
to the LLVM_DEBUG() one.
Differential Revision: https://reviews.llvm.org/D43624
llvm-svn: 332240
We've been running doxygen with the autobrief option for a couple of
years now. This makes the \brief markers into our comments
redundant. Since they are a visual distraction and we don't want to
encourage more \brief markers in new code either, this patch removes
them all.
Patch produced by
for i in $(git grep -l '\\brief'); do perl -pi -e 's/\\brief //g' $i & done
Differential Revision: https://reviews.llvm.org/D46290
llvm-svn: 331272
See r331124 for how I made a list of files missing the include.
I then ran this Python script:
for f in open('filelist.txt'):
f = f.strip()
fl = open(f).readlines()
found = False
for i in xrange(len(fl)):
p = '#include "llvm/'
if not fl[i].startswith(p):
continue
if fl[i][len(p):] > 'Config':
fl.insert(i, '#include "llvm/Config/llvm-config.h"\n')
found = True
break
if not found:
print 'not found', f
else:
open(f, 'w').write(''.join(fl))
and then looked through everything with `svn diff | diffstat -l | xargs -n 1000 gvim -p`
and tried to fix include ordering and whatnot.
No intended behavior change.
llvm-svn: 331184
Summary:
Previously the flag intrinsics always used the index instructions even if a mask instruction also exists.
To fix fix this I've created a single ISD node type that returns index, mask, and flags. The SelectionDAG CSE process will merge all flavors of intrinsics with the same inputs to a s ingle node. Then during isel we just have to look at which results are used to know what instruction to generate. If both mask and index are used we'll need to emit two instructions. But for all other cases we can emit a single instruction.
Since I had to do manual isel anyway, I've removed the pseudo instructions and custom inserter code that was working around tablegen limitations with multiple implicit defs.
I've also renamed the recently added sse42.ll test case to sttni.ll since it focuses on that subset of the sse4.2 instructions.
Reviewers: chandlerc, RKSimon, spatel
Reviewed By: chandlerc
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D46202
llvm-svn: 331091
Prefer to use the 32-bit AND with immediate instead.
Primarily I'm doing this to ensure that immediates created by shrinkAndImmediate will always get absorbed into the AND. But I do believe this would be a reduction in the number of uops that need to execute. Ideally we should shrink the 'and' and the 'load' during DAG combine to re-enable the fold.
Fixes PR37063.
llvm-svn: 329667
As in SystemZ backend, correctly propagate node ids when inserting new
unselected nodes into the DAG during instruction Seleciton for X86
target.
Fixes PR36865.
Reviewers: jyknight, craig.topper
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D44797
llvm-svn: 328233
This prevents a crash in SelectionDAGDumper with -debug when trying to print mem operands if one of the registers in the addressing mode comes from a load.
llvm-svn: 327744
We previously avoided inserting these moves during isel in a few cases which is implemented using a whitelist of opcodes. But it's too difficult to generate a perfect list of opcodes to whitelist. Especially with AVX512F without AVX512VL using 512 bit vectors to implement some 128/256 bit operations. Since isel is done bottoms up, we'd have to check the VT and opcode and subtarget in order to determine whether an EXTRACT_SUBREG would be generated for some operations.
So instead of doing that, this patch adds a post processing step that detects when the moves are unnecesssary after isel. At that point any EXTRACT_SUBREGs would have already been created and appear in the DAG. So then we just need to ensure the input to the move isn't one.
Differential Revision: https://reviews.llvm.org/D44289
llvm-svn: 327724
r327171 "Improve Dependency analysis when doing multi-node Instruction Selection"
r328170 "[DAG] Enforce stricter NodeId invariant during Instruction selection"
Reverting patch as NodeId invariant change is causing pathological
increases in compile time on PPC
llvm-svn: 327197
Relanding after fixing NodeId Invariant.
Cleanup cycle/validity checks in ISel (IsLegalToFold,
HandleMergeInputChains) and X86 (isFusableLoadOpStore). Now do a full
search for cycles / dependencies pruning the search when topological
property of NodeId allows.
As part of this propogate the NodeId-based cutoffs to narrow
hasPreprocessorHelper searches.
Reviewers: craig.topper, bogner
Subscribers: llvm-commits, hiraditya
Differential Revision: https://reviews.llvm.org/D41293
llvm-svn: 327171
Instruction Selection makes use of the topological ordering of nodes
by node id (a node's operands have smaller node id than it) when doing
cycle detection. During selection we may violate this property as a
selection of multiple nodes may induce a use dependence (and thus a
node id restriction) between two unrelated nodes. If a selected node
has an unselected successor this may allow us to miss a cycle in
detection an invalid selection.
This patch fixes this by marking all unselected successors of a
selected node have negated node id. We avoid pruning on such negative
ids but still can reconstruct the original id for pruning.
In-tree targets have been updated to replace DAG-level replacements
with ISel-level ones which enforce this property.
This preemptively fixes PR36312 before triggering commit r324359 relands
Reviewers: craig.topper, bogner, jyknight
Subscribers: arsenm, nhaehnle, javed.absar, llvm-commits, hiraditya
Differential Revision: https://reviews.llvm.org/D43198
llvm-svn: 327170
An extract_element where the result type is larger than the scalar element type is semantically an any_extend of from the scalar element type to the result type. If we expect zeroes in the upper bits of the i8/i32 we need to mae sure those zeroes are explicit in the DAG.
For these cases the best way to accomplish this is use an insert_subvector to pad zeroes to the upper bits of the v1i1 first. We extend to either v16i1(for i32) or v8i1(for i8). Then bitcast that to a scalar and finish with a zero_extend up to i32 if necessary. We can't extend past v16i1 because that's the largest mask size on KNL. But isel is smarter enough to know that a zext of a bitcast from v16i1 to i16 can use a KMOVW instruction. The insert_subvectors will be dropped during isel because we can determine that the producing instruction already zeroed the upper bits of the k-register.
llvm-svn: 326308
Sadly, r324359 caused at least PR36312. There is a patch out for review
but it seems to be taking a bit and we've already had these crashers in
tree for too long. We're hitting this PR in real code now and are
blocked on shipping new compilers as a consequence so I'm reverting us
back to green.
Sorry for the churn due to the stacked changes that I had to revert. =/
llvm-svn: 325420
We can't fold a large immediate into a 64-bit operation. But if we know we're only operating on a single bit we can use the bit instructions.
For now only do this for optsize.
Differential Revision: https://reviews.llvm.org/D37418
llvm-svn: 325287
I don't believe we ever create an X86ISD::SUB with a 0 constant which is what the TEST handling needs. The ternary operator at the end of this code shows up as only going one way in the llvm-cov report from the bots.
llvm-svn: 324865
Instruction Selection
Cleanup cycle/validity checks in ISel (IsLegalToFold,
HandleMergeInputChains) and X86 (isFusableLoadOpStore). Now do a full
search for cycles / dependencies pruning the search when topological
property of NodeId allows.
As part of this propogate the NodeId-based cutoffs to narrow
hasPreprocessorHelper searches.
Reviewers: craig.topper, bogner
Subscribers: llvm-commits, hiraditya
Differential Revision: https://reviews.llvm.org/D41293
llvm-svn: 324359
If the upper 32 bits of a 64 bit mask are all zeros, we have special isel patterns to use a 32-bit and instead of a 64-bit and by relying on the impliciting zeroing of 32 bit ops.
This patch teachs shrinkAndImmediate not to break that optimization.
Differential Revision: https://reviews.llvm.org/D42899
llvm-svn: 324249
Summary:
EmitTest sometimes creates X86ISD::AND specifically to hide the AND from DAG combine. But this prevents isel patterns that look for (cmp (and X, Y), 0) from being able to see it. So we end up with an AND and a TEST. The TEST gets removed by compare instruction optimization during the peephole pass.
This patch attempts to fix this by converting X86ISD::AND with no flag users back into ISD::AND during the DAG preprocessing just before isel.
In order to do this correctly I had to make the X86ISD::AND node created by EmitTest in this case really have a flag output. Which arguably it should have had anyway so that the number of operands would be consistent for the opcode in all cases. Then I had to modify the ReplaceAllUsesWith to understand that we might be looking at an instruction with 2 outputs. Though in this case there are no uses to replace since we just created the node, but that's what the code did before so I just made it keep working.
Reviewers: spatel, RKSimon, niravd, deadalnix
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D42764
llvm-svn: 323982
Summary:
This was introduced in D42646 but ended up being reverted because the original implementation was buggy.
Depends on D42646
Reviewers: craig.topper, niravd, spatel, hfinkel
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D42741
llvm-svn: 323899
Summary:
It seems it's main effect is to create addition copies when values are inr register that do not support this trick, which increase register pressure and makes the code bigger.
Reviewers: craig.topper, niravd, spatel, hfinkel
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D42646
llvm-svn: 323888
Summary:
It seems it's main effect is to create addition copies when values are inr register that do not support this trick, which increase register pressure and makes the code bigger.
The main noteworthy regression I was able to observe was pattern of the type (setcc (trunc (and X, C)), 0) where C is such as it would benefit from the hi register trick. To prevent this, a new pattern is added to materialize such pattern using a 32 bits test. This has the added benefit of working with any constant that is materializable as a 32bits immediate, not just the ones that can leverage the high register trick, as demonstrated by the test case in test-shrink.ll using the constant 2049 .
Reviewers: craig.topper, niravd, spatel, hfinkel
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D42646
llvm-svn: 323690
Legalization is still biased to turn LT compares in to GT by swapping operands to avoid needing extra isel patterns to commute.
I'm hoping to remove TESTM/TESTNM next and this should simplify that by making EQ/NE more similar.
llvm-svn: 323604
Previously some targets printed their own message at the start of Select to indicate what they were selecting. For the targets that didn't, it means there was no print of the root node before any custom handling in the target executed. So if the target did something custom and never called SelectNodeCommon, no print would be made. For the targets that did print a message in Select, if they didn't custom handle a node SelectNodeCommon would reprint the root node before walking the isel table.
It seems better to just print the message before the call to Select so all targets behave the same. And then remove the root node printing from SelectNodeCommon and just leave a message that says we're starting the table search.
There were also some oddities in blank line behavior. Usually due to a \n after a call to SelectionDAGNode::dump which already inserted a new line.
llvm-svn: 323551
Summary:
First, we need to explain the core of the vulnerability. Note that this
is a very incomplete description, please see the Project Zero blog post
for details:
https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html
The basis for branch target injection is to direct speculative execution
of the processor to some "gadget" of executable code by poisoning the
prediction of indirect branches with the address of that gadget. The
gadget in turn contains an operation that provides a side channel for
reading data. Most commonly, this will look like a load of secret data
followed by a branch on the loaded value and then a load of some
predictable cache line. The attacker then uses timing of the processors
cache to determine which direction the branch took *in the speculative
execution*, and in turn what one bit of the loaded value was. Due to the
nature of these timing side channels and the branch predictor on Intel
processors, this allows an attacker to leak data only accessible to
a privileged domain (like the kernel) back into an unprivileged domain.
The goal is simple: avoid generating code which contains an indirect
branch that could have its prediction poisoned by an attacker. In many
cases, the compiler can simply use directed conditional branches and
a small search tree. LLVM already has support for lowering switches in
this way and the first step of this patch is to disable jump-table
lowering of switches and introduce a pass to rewrite explicit indirectbr
sequences into a switch over integers.
However, there is no fully general alternative to indirect calls. We
introduce a new construct we call a "retpoline" to implement indirect
calls in a non-speculatable way. It can be thought of loosely as
a trampoline for indirect calls which uses the RET instruction on x86.
Further, we arrange for a specific call->ret sequence which ensures the
processor predicts the return to go to a controlled, known location. The
retpoline then "smashes" the return address pushed onto the stack by the
call with the desired target of the original indirect call. The result
is a predicted return to the next instruction after a call (which can be
used to trap speculative execution within an infinite loop) and an
actual indirect branch to an arbitrary address.
On 64-bit x86 ABIs, this is especially easily done in the compiler by
using a guaranteed scratch register to pass the target into this device.
For 32-bit ABIs there isn't a guaranteed scratch register and so several
different retpoline variants are introduced to use a scratch register if
one is available in the calling convention and to otherwise use direct
stack push/pop sequences to pass the target address.
This "retpoline" mitigation is fully described in the following blog
post: https://support.google.com/faqs/answer/7625886
We also support a target feature that disables emission of the retpoline
thunk by the compiler to allow for custom thunks if users want them.
These are particularly useful in environments like kernels that
routinely do hot-patching on boot and want to hot-patch their thunk to
different code sequences. They can write this custom thunk and use
`-mretpoline-external-thunk` *in addition* to `-mretpoline`. In this
case, on x86-64 thu thunk names must be:
```
__llvm_external_retpoline_r11
```
or on 32-bit:
```
__llvm_external_retpoline_eax
__llvm_external_retpoline_ecx
__llvm_external_retpoline_edx
__llvm_external_retpoline_push
```
And the target of the retpoline is passed in the named register, or in
the case of the `push` suffix on the top of the stack via a `pushl`
instruction.
There is one other important source of indirect branches in x86 ELF
binaries: the PLT. These patches also include support for LLD to
generate PLT entries that perform a retpoline-style indirection.
The only other indirect branches remaining that we are aware of are from
precompiled runtimes (such as crt0.o and similar). The ones we have
found are not really attackable, and so we have not focused on them
here, but eventually these runtimes should also be replicated for
retpoline-ed configurations for completeness.
For kernels or other freestanding or fully static executables, the
compiler switch `-mretpoline` is sufficient to fully mitigate this
particular attack. For dynamic executables, you must compile *all*
libraries with `-mretpoline` and additionally link the dynamic
executable and all shared libraries with LLD and pass `-z retpolineplt`
(or use similar functionality from some other linker). We strongly
recommend also using `-z now` as non-lazy binding allows the
retpoline-mitigated PLT to be substantially smaller.
When manually apply similar transformations to `-mretpoline` to the
Linux kernel we observed very small performance hits to applications
running typical workloads, and relatively minor hits (approximately 2%)
even for extremely syscall-heavy applications. This is largely due to
the small number of indirect branches that occur in performance
sensitive paths of the kernel.
When using these patches on statically linked applications, especially
C++ applications, you should expect to see a much more dramatic
performance hit. For microbenchmarks that are switch, indirect-, or
virtual-call heavy we have seen overheads ranging from 10% to 50%.
However, real-world workloads exhibit substantially lower performance
impact. Notably, techniques such as PGO and ThinLTO dramatically reduce
the impact of hot indirect calls (by speculatively promoting them to
direct calls) and allow optimized search trees to be used to lower
switches. If you need to deploy these techniques in C++ applications, we
*strongly* recommend that you ensure all hot call targets are statically
linked (avoiding PLT indirection) and use both PGO and ThinLTO. Well
tuned servers using all of these techniques saw 5% - 10% overhead from
the use of retpoline.
We will add detailed documentation covering these components in
subsequent patches, but wanted to make the core functionality available
as soon as possible. Happy for more code review, but we'd really like to
get these patches landed and backported ASAP for obvious reasons. We're
planning to backport this to both 6.0 and 5.0 release streams and get
a 5.0 release with just this cherry picked ASAP for distros and vendors.
This patch is the work of a number of people over the past month: Eric, Reid,
Rui, and myself. I'm mailing it out as a single commit due to the time
sensitive nature of landing this and the need to backport it. Huge thanks to
everyone who helped out here, and everyone at Intel who helped out in
discussions about how to craft this. Also, credit goes to Paul Turner (at
Google, but not an LLVM contributor) for much of the underlying retpoline
design.
Reviewers: echristo, rnk, ruiu, craig.topper, DavidKreitzer
Subscribers: sanjoy, emaste, mcrosier, mgorny, mehdi_amini, hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D41723
llvm-svn: 323155
Try to reverse the constant-shrinking that happens in SimplifyDemandedBits()
for 'and' masks when it results in a smaller sign-extended immediate.
We are also able to detect dead 'and' ops here (the mask is all ones). In
that case, we replace and return without selecting the 'and'.
Other targets might want to share some of this logic by enabling this under a
target hook, but I didn't see diffs for simple cases with PowerPC or AArch64,
so they may already have some specialized logic for this kind of thing or have
different needs.
This should solve PR35907:
https://bugs.llvm.org/show_bug.cgi?id=35907
Differential Revision: https://reviews.llvm.org/D42088
llvm-svn: 322957
Currently we infer the scale at isel time by analyzing whether the base is a constant 0 or not. If it is we assume scale is 1, else we take it from the element size of the pass thru or stored value. This seems a little weird and I think it makes more sense to make it explicit in the DAG rather than doing tricky things in the backend.
Most of this patch is just making sure we copy the scale around everywhere.
Differential Revision: https://reviews.llvm.org/D40055
llvm-svn: 322210
Summary:
There are few oddities that occur due to v1i1, v8i1, v16i1 being legal without v2i1 and v4i1 being legal when we don't have VLX. Particularly during legalization of v2i32/v4i32/v2i64/v4i64 masked gather/scatter/load/store. We end up promoting the mask argument to these during type legalization and then have to widen the promoted type to v8iX/v16iX and truncate it to get the element size back down to v8i1/v16i1 to use a 512-bit operation. Since need to fill the upper bits of the mask we have to fill with 0s at the promoted type.
It would be better if we could just have the v2i1/v4i1 types as legal so they don't undergo any promotion. Then we can just widen with 0s directly in a k register. There are no real v4i1/v2i1 instructions anyway. Everything is done on a larger register anyway.
This also fixes an issue that we couldn't implement a masked vextractf32x4 from zmm to xmm properly.
We now have to support widening more compares to 512-bit to get a mask result out so new tablegen patterns got added.
I had to hack the legalizer for widening the operand of a setcc a bit so it didn't try create a setcc returning v4i32, extract from it, then try to promote it using a sign extend to v2i1. Now we create the setcc with v4i1 if the original setcc's result type is v2i1. Then extract that and don't sign extend it at all.
There's definitely room for improvement with some follow up patches.
Reviewers: RKSimon, zvi, guyblank
Reviewed By: RKSimon
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D41560
llvm-svn: 321967
Hiroshi Yamauchi