Currently, we have some confusion in the codebase regarding the
meaning of LocationSize::unknown(): Some parts (including most of
BasicAA) assume that LocationSize::unknown() only allows accesses
after the base pointer. Some parts (various callers of AA) assume
that LocationSize::unknown() allows accesses both before and after
the base pointer (but within the underlying object).
This patch splits up LocationSize::unknown() into
LocationSize::afterPointer() and LocationSize::beforeOrAfterPointer()
to make this completely unambiguous. I tried my best to determine
which one is appropriate for all the existing uses.
The test changes in cs-cs.ll in particular illustrate a previously
clearly incorrect AA result: We were effectively assuming that
argmemonly functions were only allowed to access their arguments
after the passed pointer, but not before it. I'm pretty sure that
this was not intentional, and it's certainly not specified by
LangRef that way.
Differential Revision: https://reviews.llvm.org/D91649
This strips out a lot of the code that should no longer be needed from
the MVETailPredictionPass, leaving the important part - find active lane
mask instructions and convert them to VCTP operations.
Differential Revision: https://reviews.llvm.org/D91866
Patch fixes scheduling of ALU instructions which modify pc register. Patch
also fixes computation of mutually exclusive predicates for sequences of
variants to be properly expanded
Differential revision: https://reviews.llvm.org/D91266
X86 was already specially marking fma as commutable which allowed
tablegen to autogenerate commuted patterns. This moves it to the target
independent definition and fix up the targets to remove now
unneeded patterns.
Unfortunately, the tests change because the commuted version of
the patterns are generating operands in a different than the
explicit patterns.
Differential Revision: https://reviews.llvm.org/D91842
This checks to see if the loop will likely become a tail predicated loop
and disables wls loop generation if so, as the likelihood for reverting
is currently too high. These should be fairly rare situations anyway due
to the way iterations and element counts are used during lowering. Just
not trying can alter how SCEV's are materialized however, leading to
different codegen.
It also adds a option to disable all while low overhead loops, for
debugging.
Differential Revision: https://reviews.llvm.org/D91663
This converts the intermediate VPR use assertion to a condition in the if-statement to protect against assertion failures in case behaviuour is changed.
This is a follow-up to https://reviews.llvm.org/D90935 and implements the post-approval comments.
Reviewed By: dmgreen
Differential Revision: https://reviews.llvm.org/D91790
This was already something that was handled by one of the "else"
branches in maybeLoweredToCall, so this patch is an NFC but makes it
explicit and adds a test. We may in the future want to support this
under certain situations but for the moment just don't try and create
low overhead loops with inline asm in them.
Differential Revision: https://reviews.llvm.org/D91257
2c196bbc6b asserted that
`SmallVector::push_back` doesn't invalidate the parameter when it needs
to grow. Do the same for `resize`, `append`, `assign`, `insert`, and
`emplace_back`.
Differential Revision: https://reviews.llvm.org/D91744
This patch factors out the part of printInstruction that gets the
mnemonic string for a given MCInst. This is intended to be used
subsequently for the instruction-mix remarks to display the final
mnemonic (D90040).
Unfortunately making `getMnemonic` available to the AsmPrinter
seems to require making it virtual. Not sure if there's a way around
that with the current layering of the AsmPrinters.
Reviewed By: Paul-C-Anagnostopoulos
Differential Revision: https://reviews.llvm.org/D90039
This patch adds the SchedMachineModel for Cortex-M7. It
also adds test cases for the scheduling information.
Details of the pipeline and descriptions are in comments
in file ARMScheduleM7.td included in this patch.
Differential Revision: https://reviews.llvm.org/D91355
No longer rely on an external tool to build the llvm component layout.
Instead, leverage the existing `add_llvm_componentlibrary` cmake function and
introduce `add_llvm_component_group` to accurately describe component behavior.
These function store extra properties in the created targets. These properties
are processed once all components are defined to resolve library dependencies
and produce the header expected by llvm-config.
Differential Revision: https://reviews.llvm.org/D90848
Of course there was something missing, in this case a check that the def
of the count register we are adding to a t2DoLoopStartTP would dominate
the insertion point.
In the future, when we remove some of these COPY's in between, the
t2DoLoopStartTP will always become the last instruction in the block,
preventing this from happening. In the meantime we need to check they
are created in a sensible order.
Differential Revision: https://reviews.llvm.org/D91287
We have a frequent pattern where we're merging two KnownBits to get the common/shared bits, and I just fell for the gotcha where I tried to use the & operator to merge them........
Previously we used setRegClass to rgpr, which may expand the register
domain if the result was already in a constrained class (tcgpr in the
above PR).
Differential Revision: https://reviews.llvm.org/D91192
This introduces a new pseudo instruction, almost identical to a
t2DoLoopStart but taking 2 parameters - the original loop iteration
count needed for a low overhead loop, plus the VCTP element count needed
for a DLSTP instruction setting up a tail predicated loop. The idea is
that the instruction holds both values and the backend
ARMLowOverheadLoops pass can pick between the two, depending on whether
it creates a tail predicated loop or falls back to a low overhead loop.
To do that there needs to be something that converts a t2DoLoopStart to
a t2DoLoopStartTP, for which this patch repurposes the
MVEVPTOptimisationsPass as a "tail predication and vpt optimisation"
pass. The extra operand for the t2DoLoopStartTP is chosen based on the
operands of VCTP's in the loop, and the instruction is moved as late in
the block as possible to attempt to increase the likelihood of making
tail predicated loops.
Differential Revision: https://reviews.llvm.org/D90591
We already do not unroll loops with vector instructions under MVE, but
that does not include the remainder loops that the vectorizer produces.
These remainder loops will be rarely executed and are not worth
unrolling, as the trip count is likely to be low if they get executed at
all. Luckily they get llvm.loop.isvectorized to make recognizing them
simpler.
We have wanted to do this for a while but hit issues with low overhead
loops being reverted due to difficult registry allocation. With recent
changes that seems to be less of an issue now.
Differential Revision: https://reviews.llvm.org/D90055
This hints the operand of a t2DoLoopStart towards using LR, which can
help make it more likely to become t2DLS lr, lr. This makes it easier to
move if needed (as the input is the same as the output), or potentially
remove entirely.
The hint is added after others (from COPY's etc) which still take
precedence. It needed to find a place to add the hint, which currently
uses the post isel custom inserter.
Differential Revision: https://reviews.llvm.org/D89883
This changes the definition of t2DoLoopStart from
t2DoLoopStart rGPR
to
GPRlr = t2DoLoopStart rGPR
This will hopefully mean that low overhead loops are more tied together,
and we can more reliably generate loops without reverting or being at
the whims of the register allocator.
This is a fairly simple change in itself, but leads to a number of other
required alterations.
- The hardware loop pass, if UsePhi is set, now generates loops of the
form:
%start = llvm.start.loop.iterations(%N)
loop:
%p = phi [%start], [%dec]
%dec = llvm.loop.decrement.reg(%p, 1)
%c = icmp ne %dec, 0
br %c, loop, exit
- For this a new llvm.start.loop.iterations intrinsic was added, identical
to llvm.set.loop.iterations but produces a value as seen above, gluing
the loop together more through def-use chains.
- This new instrinsic conceptually produces the same output as input,
which is taught to SCEV so that the checks in MVETailPredication are not
affected.
- Some minor changes are needed to the ARMLowOverheadLoop pass, but it has
been left mostly as before. We should now more reliably be able to tell
that the t2DoLoopStart is correct without having to prove it, but
t2WhileLoopStart and tail-predicated loops will remain the same.
- And all the tests have been updated. There are a lot of them!
This patch on it's own might cause more trouble that it helps, with more
tail-predicated loops being reverted, but some additional patches can
hopefully improve upon that to get to something that is better overall.
Differential Revision: https://reviews.llvm.org/D89881
This was accidentally using the same name for two different variables in
the same line. Whilst it seems to work for some compilers, others have
trouble and it is probably not a fantastic idea.
This patch make the outliner emit CFI instructions in a few more
places:
* after LR is restored, but before the return in an outlined
function
* around save/restore of LR to/from a register at calls to outlined
functions
* around save/restore of LR to/from the stack at calls to outlined
functions
The latter two only when the function does NOT spill LR. If the
function spills LR, then outliner generated saves/restores around
calls are not considered interesting for unwinding the frame.
Differential Revision: https://reviews.llvm.org/D89483
There were cases where a VCMP and a VPST were merged even if the VCMP
didn't have the same defs of its operands as the VPST. This is fixed by
adding RDA checks for the defs. This however gave rise to cases where
the new VPST created would precede the un-merged VCMP and so would fail
a predicate mask assertion since the VCMP wasn't predicated. This was
solved by converting the VCMP to a VPT instead of inserting the new
VPST.
Differential Revision: https://reviews.llvm.org/D90461
When we fold a VCMP into a VPST instruction any kill flags between the
old VCMP position and the new insertion point need to be removed, in
order to keep the verifier happy.
Differential Revision: https://reviews.llvm.org/D90964
Add support for the Neoverse V1 CPU to the ARM and AArch64 backends.
This is based on patches from Mark Murray and Victor Campos.
Reviewed By: dmgreen
Differential Revision: https://reviews.llvm.org/D90765
This is the cmp/sel sibling to D90692.
Again, the reasoning is: the throughput cost is number of instructions/uops,
so size/blended costs are identical except in special cases (for example,
fdiv or other known-expensive machine instructions or things like MVE that
may require cracking into >1 uops).
We need to check for a valid (non-null) condition type parameter because
SimplifyCFG may pass nullptr for that (and so we will crash multiple
regression tests without that check). I'm not sure if passing nullptr makes
sense, but other code in the cost model does appear to check if that param
is set or not.
Differential Revision: https://reviews.llvm.org/D90781
To accommodate frame layouts that have both fixed and scalable objects
on the stack, describing a stack location or offset using a pointer + uint64_t
is not sufficient. For this reason, we've introduced the StackOffset class,
which models both the fixed- and scalable sized offsets.
The TargetFrameLowering::getFrameIndexReference is made to return a StackOffset,
so that this can be used in other interfaces, such as to eliminate frame indices
in PEI or to emit Debug locations for variables on the stack.
This patch is purely mechanical and doesn't change the behaviour of how
the result of this function is used for fixed-sized offsets. The patch adds
various checks to assert that the offset has no scalable component, as frame
offsets with a scalable component are not yet supported in various places.
Reviewed By: arsenm
Differential Revision: https://reviews.llvm.org/D90018
Hook up legalizations for VECREDUCE_SEQ_FMUL. This is following up on the VECREDUCE_SEQ_FADD work from D90247.
Differential Revision: https://reviews.llvm.org/D90644
This is based on the same idea that I am using for the basic model implementation
and what I have partly already done for x86: throughput cost is number of
instructions/uops, so size/blended costs are identical except in special cases
(for example, fdiv or other known-expensive machine instructions or things like
MVE that may require cracking into >1 uop)).
Differential Revision: https://reviews.llvm.org/D90692
If an instruction will be lowered to a call there is no advantage of
using a low overhead loop as the LR register will need to be spilled and
reloaded around the call, and the low overhead will end up being
reverted. This teaches our hardware loop lowering that these memory
intrinsics will be calls under certain situations.
Differential Revision: https://reviews.llvm.org/D90439
The `LiveRegUnits` utility (as well as `LivePhysRegs`) considers
callee-saved registers to be alive at the point after the return
instruction in a block. In the ARM backend, the `LR` register is
classified as callee-saved, which is not really correct (from an ARM
eABI or just common sense point of view). These two conditions cause
the `MachineOutliner` to overestimate the liveness of `LR`, which
results in unnecessary saves/restores of `LR` around calls to outlined
sequences. It also causes the `MachineVerifer` to crash in some
cases, because the save instruction reads a dead `LR`, for example
when the following program:
int h(int, int);
int f(int a, int b, int c, int d) {
a = h(a + 1, b - 1);
b = b + c;
return 1 + (2 * a + b) * (c - d) / (a - b) * (c + d);
}
int g(int a, int b, int c, int d) {
a = h(a - 1, b + 1);
b = b + c;
return 2 + (2 * a + b) * (c - d) / (a - b) * (c + d);
}
is compiled with `-target arm-eabi -march=armv7-m -Oz`.
This patch computes the liveness of `LR` in return blocks only, while
taking into account the few ARM instructions, which read `LR`, but
nevertheless the register is not mentioned (explicitly or implicitly)
in the instruction operands.
Differential Revision: https://reviews.llvm.org/D89189
This reverts the revert commit 408c4408fa.
This version of the patch includes a fix for a crash caused by
treating ICmp/FCmp constant expressions as instructions.
Original message:
On some targets, like AArch64, vector selects can be efficiently lowered
if the vector condition is a compare with a supported predicate.
This patch adds a new argument to getCmpSelInstrCost, to indicate the
predicate of the feeding select condition. Note that it is not
sufficient to use the context instruction when querying the cost of a
vector select starting from a scalar one, because the condition of the
vector select could be composed of compares with different predicates.
This change greatly improves modeling the costs of certain
compare/select patterns on AArch64.
I am also planning on putting up patches to make use of the new argument in
SLPVectorizer & LV.
Patch fixes case when sched class has write and read variants belonging
to different processor models.
Differential revision: https://reviews.llvm.org/D89777
If the elt size is unknown due to it being a pointer, a comparison
against 0 will cause an assert. Make sure the elt size is large enough
before comparing and for the moment just return the scalar cost.
Add Legalization support for VECREDUCE_SEQ_FADD, so that we don't need to depend on ExpandReductionsPass.
Differential Revision: https://reviews.llvm.org/D90247
On some targets, like AArch64, vector selects can be efficiently lowered
if the vector condition is a compare with a supported predicate.
This patch adds a new argument to getCmpSelInstrCost, to indicate the
predicate of the feeding select condition. Note that it is not
sufficient to use the context instruction when querying the cost of a
vector select starting from a scalar one, because the condition of the
vector select could be composed of compares with different predicates.
This change greatly improves modeling the costs of certain
compare/select patterns on AArch64.
I am also planning on putting up patches to make use of the new argument in
SLPVectorizer & LV.
Reviewed By: dmgreen, RKSimon
Differential Revision: https://reviews.llvm.org/D90070
This adds ISel matching for a form of VQDMULH. There are several ir
patterns that we could match to that instruction, this one is for:
min(ashr(mul(sext(a), sext(b)), 7), 127)
Which is what llvm will optimize to once it has removed the max that
usually makes up the min/max saturate pattern, as in this case the
compare will always be false. The additional complication to match i32
patterns (which extend into an i64) is that the min will be a
vselect/setcc, as vmin is not supported for i64 vectors. Tablegen
patterns have also been updated to attempt to reuse the MVE_TwoOpPattern
patterns.
Differential Revision: https://reviews.llvm.org/D90096
Fixes a regression caused by D82439, in which IT blocks were no longer being generated when -Oz is present.
Differential Revision: https://reviews.llvm.org/D88496
This adds a MultiHazardRecognizer and starts to make use of it in the
ARM backend. The idea of the class is to allow multiple independent
hazard recognizers to be added to a single base MultiHazardRecognizer,
allowing them to all work in parallel without requiring them to be
chained into subclasses. They can then be added or not based on cpu or
subtarget features, which will become useful in the ARM backend once
more hazard recognizers are being used for various things.
This also renames ARMHazardRecognizer to ARMHazardRecognizerFPMLx in the
process, to more clearly explain what that recognizer is designed for.
Differential Revision: https://reviews.llvm.org/D72939
Some instructions may be removable through processes such as IfConversion,
however DefinesPredicate can not be made aware of when this should be considered.
This parameter allows DefinesPredicate to distinguish these removable instructions
on a per-call basis, allowing for more fine-grained control from processes like
ifConversion.
Renames DefinesPredicate to ClobbersPredicate, to better reflect it's purpose
Differential Revision: https://reviews.llvm.org/D88494
This reverts commit 38f625d0d1.
This commit contains some holes in its logic and has been causing
issues since it was commited. The idea sounds OK but some cases were not
handled correctly. Instead of trying to fix that up later it is probably
simpler to revert it and work to reimplement it in a more reliable way.
Create the LLVM / CodeView register mappings for the 32-bit ARM Window targets.
Reviewed By: compnerd
Differential Revision: https://reviews.llvm.org/D89622
This adds some basic costs for MVE reductions - currently just costing
the simple legal add vectors as a single MVE instruction. More complex
costing can be added in the future when the framework more readily
allows it.
Differential Revision: https://reviews.llvm.org/D88980
This adds a very basic cost for active_lane_mask under MVE - making the
assumption that they will be free and then apologizing for that in a
comment.
In reality they may either be free (by being nicely folded into a tail
predicated loop), cost the same as a VCTP or be expanded into vdup's,
adds and cmp's. It is difficult to detect the difference from a single
getIntrinsicInstrCost call, so makes the assumption that the vectorizer
is adding them, and only added them where it makes sense.
We may need to change this in the future to better model predicate costs
in the vectorizer, especially at -Os or non-tail predicated loops. The
vectorizer currently does not query the cost of these instructions but
that will change in the future and a zero cost there probably makes the
most sense at the moment.
Differential Revision: https://reviews.llvm.org/D88989
In most of lib/Target we know that we are not dealing with scalable
types so it's perfectly fine to replace TypeSize comparison operators
with their fixed width equivalents, making use of getFixedSize()
and so on.
Differential Revision: https://reviews.llvm.org/D89101
There are a number of places in RDA where we assume the block will not
be empty. This isn't necessarily true for tail predicated loops where we
have removed instructions. This attempt to make the pass more resilient
to empty blocks, not casting pointers to machine instructions where they
would be invalid.
The test contains a case that was previously failing, but recently been
hidden on trunk. It contains an empty block to begin with to show a
similar error.
Differential Revision: https://reviews.llvm.org/D88926
This folds a select_cc or select(set_cc) of a max or min vector reduction with a scalar value into a VMAXV or VMINV.
Differential Revision: https://reviews.llvm.org/D87836
This folds a select_cc or select(set_cc) of a max or min vector reduction with a scalar value into a VMAXV or VMINV.
Differential Revision: https://reviews.llvm.org/D87836
We were not accounting for the pointer offset when splitting a store from
a VMOVDRR node, which could lead to incorrect aliasing info. In this
case it is the fneg via integer arithmetic that gives us a store->load
pair that we started getting wrong.
Differential Revision: https://reviews.llvm.org/D88653
Marks constants of an ICmp instruction as free if it's only user is a select
instruction that is part of a min(max()) pattern. Ensures that in loops, in
particular when loop unrolling is turned on, SSAT will still be correctly generated.
Differential Revision: https://reviews.llvm.org/D88662
Before deciding to insert a [W|D]LSTP, check that defining LR with
the element count won't affect any other instructions that should be
taking the iteration count.
Differential Revision: https://reviews.llvm.org/D88549
This is part of the Propeller framework to do post link code layout optimizations. Please see the RFC here: https://groups.google.com/forum/#!msg/llvm-dev/ef3mKzAdJ7U/1shV64BYBAAJ and the detailed RFC doc here: https://github.com/google/llvm-propeller/blob/plo-dev/Propeller_RFC.pdf
This patch provides exception support for basic block sections by splitting the call-site table into call-site ranges corresponding to different basic block sections. Still all landing pads must reside in the same basic block section (which is guaranteed by the the core basic block section patch D73674 (ExceptionSection) ). Each call-site table will refer to the landing pad fragment by explicitly specifying @LPstart (which is omitted in the normal non-basic-block section case). All these call-site tables will share their action and type tables.
The C++ ABI somehow assumes that no landing pads point directly to LPStart (which works in the normal case since the function begin is never a landing pad), and uses LP.offset = 0 to specify no landing pad. In the case of basic block section where one section contains all the landing pads, the landing pad offset relative to LPStart could actually be zero. Thus, we avoid zero-offset landing pads by inserting a **nop** operation as the first non-CFI instruction in the exception section.
**Background on Exception Handling in C++ ABI**
https://github.com/itanium-cxx-abi/cxx-abi/blob/master/exceptions.pdf
Compiler emits an exception table for every function. When an exception is thrown, the stack unwinding library queries the unwind table (which includes the start and end of each function) to locate the exception table for that function.
The exception table includes a call site table for the function, which is used to guide the exception handling runtime to take the appropriate action upon an exception. Each call site record in this table is structured as follows:
| CallSite | --> Position of the call site (relative to the function entry)
| CallSite length | --> Length of the call site.
| Landing Pad | --> Position of the landing pad (relative to the landing pad fragment’s begin label)
| Action record offset | --> Position of the first action record
The call site records partition a function into different pieces and describe what action must be taken for each callsite. The callsite fields are relative to the start of the function (as captured in the unwind table).
The landing pad entry is a reference into the function and corresponds roughly to the catch block of a try/catch statement. When execution resumes at a landing pad, it receives an exception structure and a selector value corresponding to the type of the exception thrown, and executes similar to a switch-case statement. The landing pad field is relative to the beginning of the procedure fragment which includes all the landing pads (@LPStart). The C++ ABI requires all landing pads to be in the same fragment. Nonetheless, without basic block sections, @LPStart is the same as the function @Start (found in the unwind table) and can be omitted.
The action record offset is an index into the action table which includes information about which exception types are caught.
**C++ Exceptions with Basic Block Sections**
Basic block sections break the contiguity of a function fragment. Therefore, call sites must be specified relative to the beginning of the basic block section. Furthermore, the unwinding library should be able to find the corresponding callsites for each section. To do so, the .cfi_lsda directive for a section must point to the range of call-sites for that section.
This patch introduces a new **CallSiteRange** structure which specifies the range of call-sites which correspond to every section:
`struct CallSiteRange {
// Symbol marking the beginning of the precedure fragment.
MCSymbol *FragmentBeginLabel = nullptr;
// Symbol marking the end of the procedure fragment.
MCSymbol *FragmentEndLabel = nullptr;
// LSDA symbol for this call-site range.
MCSymbol *ExceptionLabel = nullptr;
// Index of the first call-site entry in the call-site table which
// belongs to this range.
size_t CallSiteBeginIdx = 0;
// Index just after the last call-site entry in the call-site table which
// belongs to this range.
size_t CallSiteEndIdx = 0;
// Whether this is the call-site range containing all the landing pads.
bool IsLPRange = false;
};`
With N basic-block-sections, the call-site table is partitioned into N call-site ranges.
Conceptually, we emit the call-site ranges for sections sequentially in the exception table as if each section has its own exception table. In the example below, two sections result in the two call site ranges (denoted by LSDA1 and LSDA2) placed next to each other. However, their call-sites will refer to records in the shared Action Table. We also emit the header fields (@LPStart and CallSite Table Length) for each call site range in order to place the call site ranges in separate LSDAs. We note that with -basic-block-sections, The CallSiteTableLength will not actually represent the length of the call site table, but rather the reference to the action table. Since the only purpose of this field is to locate the action table, correctness is guaranteed.
Finally, every call site range has one @LPStart pointer so the landing pads of each section must all reside in one section (not necessarily the same section). To make this easier, we decide to place all landing pads of the function in one section (hence the `IsLPRange` field in CallSiteRange).
| @LPStart | ---> Landing pad fragment ( LSDA1 points here)
| CallSite Table Length | ---> Used to find the action table.
| CallSites |
| … |
| … |
| @LPStart | ---> Landing pad fragment ( LSDA2 points here)
| CallSite Table Length |
| CallSites |
| … |
| … |
…
…
| Action Table |
| Types Table |
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D73739
Just because we haven't encountered an instruction setting the VPR,
it doesn't mean we can't create a VPT block - the VPR maybe a
live-in.
Differential Revision: https://reviews.llvm.org/D88224
Added patterns to generate an SSAT or USAT with shift for
SSAT/USAT instructions that are matched from IR patterns.
Differential Revision: https://reviews.llvm.org/D88145
We have been running tests/benchmarks downstream with tail-predication enabled
for some time now and this behaves as expected: we are not aware of any
correctness issues, and this performs better across the board than with
tail-predication disabled. Time to flip the switch!
Differential Revision: https://reviews.llvm.org/D88093
This is a reimplementation of the overflow checks for the elementcount,
i.e. the 2nd argument of intrinsic get.active.lane.mask. The element
count is lowered in each iteration of the tail-predicated loop, and
we must prove that this expression doesn't overflow.
Many thanks to Eli Friedman and Sam Parker for all their help with
this work.
Differential Revision: https://reviews.llvm.org/D88086
9d9a11c7be added this check for predicatable instructions between the
D/WLSTP and the loop's start, but it was missing the last instruction in
the block. Change it to use some iterators instead.
Differential Revision: https://reviews.llvm.org/D88354
On failing to find a VCTP in the list of instructions that explicitly
predicate the entry of a VPT block, inspect whether the block is
controlled via VPT which is implicitly predicated due to it's
predicated operand(s).
Differential Revision: https://reviews.llvm.org/D87819
This might be useful for testing. We already have an option -tail-predication
but that controls the MVETailPredication pass. This
-arm-loloops-disable-tail-pred is just for disabling it in the LowoverheadLoops
pass.
Differential Revision: https://reviews.llvm.org/D88212
If the LSTP instruction is inserted with an element count low enough
to immediately predicate some lanes as false, this can have some
unintended effects on any proceeding MVE instructions in the
preheader.
Differential Revision: https://reviews.llvm.org/D88209
Previously, if a floating-point type was legal, but FNEG wasn't legal,
we would use FSUB. Instead, we should use integer ops, to preserve the
semantics. (Alternatively, there's a compiler-rt call we could use, but
there isn't much reason to use that.)
It turns out we actually are still using this obscure codepath in a few
cases: on some targets, we have "legal" floating-point types that don't
actually support any floating-point operations. In particular, ARM and
AArch64 are using this path.
The implementation for SelectionDAG is pretty simple because we can
reuse the infrastructure from FCOPYSIGN.
See also 9a3dc3e, the corresponding change to type legalization.
Also includes a "bonus" change to STRICT_FSUB legalization, so we can
lower a STRICT_FSUB to a float libcall.
Includes the changes to both LegalizeDAG and GlobalISel so we don't have
inconsistent results in the future.
Fixes https://bugs.llvm.org/show_bug.cgi?id=46792 .
Differential Revision: https://reviews.llvm.org/D84287
An existing function Type::getScalarSizeInBits returns a uint64_t
instead of a TypeSize class because the caller is requesting a
scalar size, which cannot be scalable. This patch makes other
similar functions requesting a scalar size consistent with that,
thereby eliminating more than 1000 implicit TypeSize -> uint64_t
casts.
Differential revision: https://reviews.llvm.org/D87889
Changes TTI function getIntImmCostInst to take an additional Instruction parameter,
which enables us to be able to check it is part of a min(max())/max(min()) pattern that will match SSAT.
We can then mark the constant used as free to prevent it being hoisted so SSAT can still be generated.
Required minor changes in some non-ARM backends to allow for the optional parameter to be included.
Differential Revision: https://reviews.llvm.org/D87457
The VPTBlock has been modified to track the 'global' state of the
VPR, as well as the state for each block. Each object now just holds
a list of instructions that makeup the block, while static structures
hold the predicate information. This enables global access for
querying how both a VPT block and individual instructions are
predicated. These changes now allow us, again, to handle more
complicated cases where multiple instructions build a predicate
and/or where the same predicate in used in multiple blocks.
It doesn't, however, get us back to before the tracking was 'fixed'
as some extra logic will be required to properly handle VPT
instructions. Currently a VPT could be effectively predicated because
of it's inputs, but the existing logic will not detect that and so
will refuse to perform the transformation. This can be seen in
remat-vctp.ll test where we still don't perform the transform.
Differential Revision: https://reviews.llvm.org/D87681
Remove the domain from the instructions and create a shouldInspect
helper for LowOverheadLoops which queries it or a vpr operand.
Differential Revision: https://reviews.llvm.org/D87900
security boundary
It was never supported and that part was accidentally omitted when
upstreaming D76518.
Differential Revision: https://reviews.llvm.org/D86478
Change-Id: If6ba9506eb0431c87a1d42a38aa60e47ce263039
This adds lowering for f32 values using the vmov.f16, which zeroes the
top bits whilst setting the lower bits to a pattern. This range of
values does not often come up, except where a f16 constant value has
been converted to a f32.
Differential Revision: https://reviews.llvm.org/D87790
This adds simple constant folding for VMOVrh, to constant fold fp16
constants to integer values. It can help especially with soft calling
conventions, but some of the results are not optimal as we end up
loading using a vldr. This will be improved in a follow up patch.
Differential Revision: https://reviews.llvm.org/D87789
When generating matching tables for GlobalISel, TableGen would output
"::zero_reg" whenever encountering the zero_reg, which in turn would
result in compilation error. This patch fixes that by instead outputting
NoRegister (== 0), which is the same result that TableGen produces when
generating matching tables for ISelDAG.
Reviewed By: arsenm
Differential Revision: https://reviews.llvm.org/D86215
This extends the distributing postinc code in load/store optimizer to
also handle the case where there is an existing pre/post inc instruction,
where subsequent instructions can be modified to use the adjusted
offset from the increment. This can save us having to keep the old
register live past the increment instruction.
Differential Revision: https://reviews.llvm.org/D83377
The predicated MVE intrinsics are generated as, for example,
llvm.arm.mve.add.predicated(x, splat(y). p). We need to sink the splat
value back into the loop, like we do for other instructions, so we can
re-select qr variants.
Differential Revision: https://reviews.llvm.org/D87693
Additional sanity checks were added to get.active.lane.mask's second argument,
the loop tripcount/elementcount, in rG635b87511ec3. Like the other (overflow)
checks, skip this if tail-predication is forced.
Differential Revision: https://reviews.llvm.org/D87769
Clear the CurrentPredicate when we find an instruction which would
completely overwrite the VPR. This fix essentially means we're back
to not really being able to handle VPT instructions when tail
predicating.
Differential Revision: https://reviews.llvm.org/D87610
Modify the unit test to inspect all MVE instructions and mark the
load/store/move of vpr/p0 as valid, as well as the remaining scalar
shifts.
Differential Revision: https://reviews.llvm.org/D87753
The versions that take 'unsigned' will be removed in the future.
I tried to use getOriginalAlign instead of getAlign in some
places. getAlign factors in the minimum alignment implied by
the offset in the pointer info. Since we're also passing the
pointer info we can use the original alignment.
Reviewed By: arsenm
Differential Revision: https://reviews.llvm.org/D87592
This adds SoftenFloatRes, PromoteFloatRes and SoftPromoteHalfRes
legalizations for VECREDUCE, to fill the remaining hole in the SDAG
legalization. These legalizations simply expand the reduction and
let it be recursively legalized. For the PromoteFloatRes case at
least it is possible to do better than that, but it's pretty tricky
(because we need to consider the interaction of three different
vector legalizations and the type promotion) and probably not
really worthwhile.
I haven't added ExpandFloatRes support, as I am not familiar with
ppc_fp128.
Differential Revision: https://reviews.llvm.org/D87569
LLVM will canonicalize conditional selectors to a different pattern than the old code that was used.
This is updating the function to match the new expected patterns and select SSAT or USAT when successful.
Tests have also been updated to use the new patterns.
Differential Review: https://reviews.llvm.org/D87379
This adds additional checks for the original scalar loop tripcount value, i.e.
get.active.lane.mask second argument, and perform several sanity checks to see
if it is of the form that we expect similarly like we already do for the IV
which is the first argument of get.active.lane.
Differential Revision: https://reviews.llvm.org/D86074
Treating an SoImm offset as a multiple of 4 between -1020 and 1020
mis-handles the second of a pair of 16-bit constants where the offset is a multiple of 2 but not a multiple of 4,
leading to an LLVM ERROR: out of range pc-relative fixup value
For 32-bit and larger (64-bit) constants, continue to treat an SoImm offset as a multiple of 4 between -1020 and 1020.
For smaller (16-bit) constants, treat an SoImm offset as a multiple of 1 between -255 and 255.
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D86949
This allows the backend to tell the vectorizer to produce inloop
reductions through a TTI hook.
For the moment on ARM under MVE this means allowing integer add
reductions of the correct size. In the future this can include integer
min/max too, under -Os.
Differential Revision: https://reviews.llvm.org/D75512
This fixes a complication on top of D87276. If we are sign extending
around a mul with the two operands that are the same, instcombine will
helpfully convert one of the sext to a zext. Reverse that so that we
again generate a reduction.
Differnetial Revision: https://reviews.llvm.org/D87287
As discussed on llvm-dev:
http://lists.llvm.org/pipermail/llvm-dev/2020-April/140729.html
This is hopefully the final remaining showstopper before we can remove
the 'experimental' from the reduction intrinsics.
No behavior was specified for the FP min/max reductions, so we have a
mess of different interpretations.
There are a few potential options for the semantics of these max/min ops.
I think this is the simplest based on current behavior/implementation:
make the reductions inherit from the existing llvm.maxnum/minnum intrinsics.
These correspond to libm fmax/fmin, and those are similar to the (now
deprecated?) IEEE-754 maxNum/minNum functions (NaNs are treated as missing
data). So the default expansion creates calls to libm functions.
Another option would be to inherit from llvm.maximum/minimum (NaNs propagate),
but most targets just crash in codegen when given those nodes because no
default expansion was ever implemented AFAICT.
We could also just assume 'nnan' semantics by default (we are already
assuming 'nsz' semantics in the maxnum/minnum intrinsics), but some targets
(AArch64, PowerPC) support the more defined behavior, so it doesn't make much
sense to not allow a tighter spec. Fast-math-flags (nnan) can be used to
loosen the semantics.
(Note that D67507 was proposed to update the LangRef to acknowledge the more
recent IEEE-754 2019 standard, but that patch seems to have stalled. If we do
update based on the new standard, the reduction instructions can seamlessly
inherit from whatever updates are made to the max/min intrinsics.)
x86 sees a regression here on 'nnan' tests because we have underlying,
longstanding bugs in FMF creation/propagation. Those need to be fixed apart
from this change (for example: https://llvm.org/PR35538). The expansion
sequence before this patch may not have been correct.
Differential Revision: https://reviews.llvm.org/D87391
We can sometimes get code that does:
xe = zext i16 x to i32
ye = zext i16 y to i32
m = mul i32 xe, ye
me = zext i32 m to i64
r = vecreduce.add(me)
This "double extend" can trip up the reduction identification, but
should give identical results.
This extends the pattern matching to handle them.
Differential Revision: https://reviews.llvm.org/D87276
values
The effects of unpredicated vector instruction with unknown
lanes cannot be predicted and therefore cannot be tail predicated. This
does not apply to predicated vector instructions and so this patch
allows tail predication on them.
Differential Revision: https://reviews.llvm.org/D87376
We weren't using this before, so none of the MachineFunction CFG edges had the
branch probability information added. As a result, block placement later in the
pipeline was flying blind.
This is enabled only with optimizations enabled like SelectionDAG.
Differential Revision: https://reviews.llvm.org/D86824
We really want to try and avoid spilling P0, which can be difficult
since there's only one register, so try to rematerialize any VCTP
instructions.
Differential Revision: https://reviews.llvm.org/D87280
count register
After my patch at D86087, code that now uses the mov operand rather than
the vctp operand will no longer remove modifications to the vctp operand
as they should. This patch fixes that by explicitly removing
modifications to the vctp operand rather than the register used as the
element count.
This was reverted in 503deec218
because it caused gigantic increase (3x) in branch mispredictions
in certain benchmarks on certain CPU's,
see https://reviews.llvm.org/D84108#2227365.
It has since been investigated and here are the results:
https://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20200907/827578.html
> It's an amazingly severe regression, but it's also all due to branch
> mispredicts (about 3x without this). The code layout looks ok so there's
> probably something else to deal with. I'm not sure there's anything we can
> reasonably do so we'll just have to take the hit for now and wait for
> another code reorganization to make the branch predictor a bit more happy :)
>
> Thanks for giving us some time to investigate and feel free to recommit
> whenever you'd like.
>
> -eric
So let's just reland this.
Original commit message:
I've been looking at missed vectorizations in one codebase.
One particular thing that stands out is that some of the loops
reach vectorizer in a rather mangled form, with weird PHI's,
and some of the loops aren't even in a rotated form.
After taking a more detailed look, that happened because
the loop's headers were too big by then. It is evident that
SimplifyCFG's common code hoisting transform is at fault there,
because the pattern it handles is precisely the unrotated
loop basic block structure.
Surprizingly, `SimplifyCFGOpt::HoistThenElseCodeToIf()` is enabled
by default, and is always run, unlike it's friend, common code sinking
transform, `SinkCommonCodeFromPredecessors()`, which is not enabled
by default and is only run once very late in the pipeline.
I'm proposing to harmonize this, and disable common code hoisting
until //late// in pipeline. Definition of //late// may vary,
here currently i've picked the same one as for code sinking,
but i suppose we could enable it as soon as right after
loop rotation happens.
Experimentation shows that this does indeed unsurprizingly help,
more loops got rotated, although other issues remain elsewhere.
Now, this undoubtedly seriously shakes phase ordering.
This will undoubtedly be a mixed bag in terms of both compile- and
run- time performance, codesize. Since we no longer aggressively
hoist+deduplicate common code, we don't pay the price of said hoisting
(which wasn't big). That may allow more loops to be rotated,
so we pay that price. That, in turn, that may enable all the transforms
that require canonical (rotated) loop form, including but not limited to
vectorization, so we pay that too. And in general, no deduplication means
more [duplicate] instructions going through the optimizations. But there's still
late hoisting, some of them will be caught late.
As per benchmarks i've run {F12360204}, this is mostly within the noise,
there are some small improvements, some small regressions.
One big regression i saw i fixed in rG8d487668d09fb0e4e54f36207f07c1480ffabbfd, but i'm sure
this will expose many more pre-existing missed optimizations, as usual :S
llvm-compile-time-tracker.com thoughts on this:
http://llvm-compile-time-tracker.com/compare.php?from=e40315d2b4ed1e38962a8f33ff151693ed4ada63&to=c8289c0ecbf235da9fb0e3bc052e3c0d6bff5cf9&stat=instructions
* this does regress compile-time by +0.5% geomean (unsurprizingly)
* size impact varies; for ThinLTO it's actually an improvement
The largest fallout appears to be in GVN's load partial redundancy
elimination, it spends *much* more time in
`MemoryDependenceResults::getNonLocalPointerDependency()`.
Non-local `MemoryDependenceResults` is widely-known to be, uh, costly.
There does not appear to be a proper solution to this issue,
other than silencing the compile-time performance regression
by tuning cut-off thresholds in `MemoryDependenceResults`,
at the cost of potentially regressing run-time performance.
D84609 attempts to move in that direction, but the path is unclear
and is going to take some time.
If we look at stats before/after diffs, some excerpts:
* RawSpeed (the target) {F12360200}
* -14 (-73.68%) loops not rotated due to the header size (yay)
* -272 (-0.67%) `"Number of live out of a loop variables"` - good for vectorizer
* -3937 (-64.19%) common instructions hoisted
* +561 (+0.06%) x86 asm instructions
* -2 basic blocks
* +2418 (+0.11%) IR instructions
* vanilla test-suite + RawSpeed + darktable {F12360201}
* -36396 (-65.29%) common instructions hoisted
* +1676 (+0.02%) x86 asm instructions
* +662 (+0.06%) basic blocks
* +4395 (+0.04%) IR instructions
It is likely to be sub-optimal for when optimizing for code size,
so one might want to change tune pipeline by enabling sinking/hoisting
when optimizing for size.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D84108
This reverts commit 503deec218.
When optimising for size, make the cost of i1 logical operations
relatively expensive so that optimisations don't try to combine
predicates.
Differential Revision: https://reviews.llvm.org/D86525
This adds a simple tablegen pattern for folding predicate_cast(load)
into vldr p0, providing the alignment and offset are correct.
Differential Revision: https://reviews.llvm.org/D86702
This patch implements the foldMemoryOperand hook in Thumb1InstrInfo,
allowing tBLXr and a spilled function address to be combined back into a
tBL. This can help with codesize at Oz, especailly in the tinycrypt
library.
Differential Revision: https://reviews.llvm.org/D79785
There's a special case in hasAttribute for None when pImpl is null. If pImpl is not null we dispatch to pImpl->hasAttribute which will always return false for Attribute::None.
So if we just want to check for None its sufficient to just check that pImpl is null. Which can even be done inline.
This patch adds a helper for that case which I hope will speed up our getSubtargetImpl implementations.
Differential Revision: https://reviews.llvm.org/D86744
Skip this for now, to avoid a backend crash in:
UNREACHABLE executed at llvm/lib/Target/ARM/ARMISelLowering.cpp:13412
This should fix PR45824.
Differential Revision: https://reviews.llvm.org/D86784
These arm_mve_vldr_gather_offset_predicated and
arm_mve_vstr_scatter_offset_predicated have some extra parameters
meaning the predicate is at a later operand. If a loop contains _only_
those masked instructions, we would miss transforming the active lane
mask.
Differential Revision: https://reviews.llvm.org/D86791
Remove the code that tried to look for reduction patterns, since the
vectorizer and isel can now produce predicated arithmetic instructios
within the loop body. This has required some reorganisation and fixes
around live-out and predication checks, as well as looking for cases
where an input/output is initialised to zero.
Differential Revision: https://reviews.llvm.org/D86613
This patch adjusts the following ARM/AArch64 LLVM IR intrinsics:
- neon_bfmmla
- neon_bfmlalb
- neon_bfmlalt
so that they take and return bf16 and float types. Previously these
intrinsics used <8 x i8> and <4 x i8> vectors (a rudiment from
implementation lacking bf16 IR type).
The neon_vbfdot[q] intrinsics are adjusted similarly. This change
required some additional selection patterns for vbfdot itself and
also for vector shuffles (in a previous patch) because of SelectionDAG
transformations kicking in and mangling the original code.
This patch makes the generated IR cleaner (less useless bitcasts are
produced), but it does not affect the final assembly.
Reviewed By: dmgreen
Differential Revision: https://reviews.llvm.org/D86146
Enable default outlining when the function has the minsize attribute
and we're targeting an m-class core.
Differential Revision: https://reviews.llvm.org/D82951
Fix the ARM backend's analyzeBranch so it doesn't ignore predicated
return instructions, and make the MachineVerifier rule more strict.
Differential Revision: https://reviews.llvm.org/D40061
MVE Gather scatter codegeneration is looking a lot better than it used
to, but still has some issues. The instructions we currently model as 1
cycle per element, which is a bit low for some cases. Increasing the
cost by the MVECostFactor brings them in-line with our other instruction
costs. This will have the effect of only generating then when the extra
benefit is more likely to overcome some of the issues. Notably in
running out of registers and vectorizing loops that could otherwise be
SLP vectorized.
In the short-term whilst we look at other ways of dealing with those
more directly, we can increase the costs of gathers to make them more
likely to be beneficial when created.
Differential Revision: https://reviews.llvm.org/D86444
This adapts tail-predication to the new semantics of get.active.lane.mask as
defined in D86147. This means that:
- we can remove the BTC + 1 overflow checks because now the loop tripcount is
passed in to the intrinsic,
- we can immediately use that value to setup a counter for the number of
elements processed by the loop and don't need to materialize BTC + 1.
Differential Revision: https://reviews.llvm.org/D86303
If gather/scatters are enabled, ARMTargetTransformInfo now allows
tail predication for loops with a much wider range of strides, up
to anything that is loop invariant.
Differential Revision: https://reviews.llvm.org/D85410
As disscussed in post-commit review starting with
https://reviews.llvm.org/D84108#2227365
while this appears to be mostly a win overall, especially code-size-wise,
this appears to shake //certain// code pattens in a way that is extremely
unfavorable for performance (+30% runtime regression)
on certain CPU's (i personally can't reproduce).
So until the behaviour is better understood, and a path forward is mapped,
let's back this out for now.
This reverts commit 1d51dc38d8.
Modify the ARM getCmpSelInstrCost implementation for the code size
costs of selects. Now consider the legalization cost and increase
the cost of i1 because those values wouldn't live in a general purpose
register. We also make selects +1 more expensive to account for the IT
instruction.
Differential Revision: https://reviews.llvm.org/D82091
As part of D84741, this adds a target hook for the
preferPredicatedReductionSelect option and makes use
of it under MVE, allowing us to tail predicate most
reduction loops.
Differential Revision: https://reviews.llvm.org/D85980
Use the stack to save and restore the link register when there is no
available register to do it.
Differential Revision: https://reviews.llvm.org/D76069
VLD2/4 instructions cannot be predicated, so we cannot tail predicate
them from autovec. From intrinsics though, they should be valid as they
will just end up loading extra values into off vector lanes, not
effecting the on lanes. The same is true for loads in general where so
long as we are not using the other vector lanes, an unpredicated load
can be converted to a predicated one.
This marks VLD2 and VLD4 instructions as validForTailPredication and
allows any unpredicated load in tail predication loop, which seems to be
valid given the other checks we have.
Differential Revision: https://reviews.llvm.org/D86022
There are some cases where the instruction that sets up the iteration
count for a tail predicated loop cannot be moved before the dlstp,
stopping tail predication entirely. This patch checks if the mov operand
can be used and if so, uses that instead.
Differential Revision: https://reviews.llvm.org/D86087
This patch implements initial backend support for a -mtune CPU controlled by a "tune-cpu" function attribute. If the attribute is not present X86 will use the resolved CPU from target-cpu attribute or command line.
This patch adds MC layer support a tune CPU. Each CPU now has two sets of features stored in their GenSubtargetInfo.inc tables . These features lists are passed separately to the Processor and ProcessorModel classes in tablegen. The tune list defaults to an empty list to avoid changes to non-X86. This annoyingly increases the size of static tables on all target as we now store 24 more bytes per CPU. I haven't quantified the overall impact, but I can if we're concerned.
One new test is added to X86 to show a few tuning features with mismatched tune-cpu and target-cpu/target-feature attributes to demonstrate independent control. Another new test is added to demonstrate that the scheduler model follows the tune CPU.
I have not added a -mtune to llc/opt or MC layer command line yet. With no attributes we'll just use the -mcpu for both. MC layer tools will always follow the normal CPU for tuning.
Differential Revision: https://reviews.llvm.org/D85165
These operations take Qda and Rn register operands, which are
commutative so long as the instruction is not predicated.
Differential Revision: https://reviews.llvm.org/D85813
Similar to the Two op + select patterns that were added recently, this
adds some patterns for select + fma to turn them into predicated
operations.
Differential Revision: https://reviews.llvm.org/D85824
Widen the scope of memory operations that are allowed to be tail predicated
to include gathers and scatters, such that loops that are auto-vectorized
with the option -enable-arm-maskedgatscat (and actually end up containing
an MVE gather or scatter) can be tail predicated.
Differential Revision: https://reviews.llvm.org/D85138
When TTI was updated to use an explicit cost, TCK_CodeSize was used
although the default implicit cost would have been the hand-wavey
cost of size and latency. So, revert back to this behaviour. This is
not expected to have (much) impact on targets since most (all?) of
them return the same value for SizeAndLatency and CodeSize.
When optimising for size, the logic has been changed to query
CodeSize costs instead of SizeAndLatency.
This patch also adds a testing option in the unroller so that
OptSize thresholds can be specified.
Differential Revision: https://reviews.llvm.org/D85723
This pick ups the work on the overflow checks for get.active.lane.mask,
which ensure that it is safe to insert the VCTP intrinisc that enables
tail-predication. For a 2d auto-correlation kernel and its inner loop j:
M = Size - i;
for (j = 0; j < M; j++)
Sum += Input[j] * Input[j+i];
For this inner loop, the SCEV backedge taken count (BTC) expression is:
(-1 + (sext i16 %Size to i32)),+,-1}<nw><%for.body>
and LoopUtil cannotBeMaxInLoop couldn't calculate a bound on this, thus "BTC
cannot be max" could not be determined. So overflow behaviour had to be assumed
in the loop tripcount expression that uses the BTC. As a result
tail-predication had to be forced (with an option) for this case.
This change solves that by using ScalarEvolution's helper
getConstantMaxBackedgeTakenCount which is able to determine the range of BTC,
thus can determine it is safe, so that we no longer need to force tail-predication
as reflected in the changed test cases.
Differential Revision: https://reviews.llvm.org/D85737
Changes the Offset arguments to both functions from int64_t to TypeSize
& updates all uses of the functions to create the offset using TypeSize::Fixed()
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D85220
IT blocks with more than one instruction were performance deprecated in Armv8
but that doesn't mean we should follow that advise when optimising for size.
Differential Revision: https://reviews.llvm.org/D85638
This adds patterns for v16i16's vecreduce, using all the existing code
to go via an i32 VADDV/VMLAV and truncating the result.
Differential Revision: https://reviews.llvm.org/D85452
This formats some of the MVE patterns, and adds a missing
Predicates = [HasMVEInt] to some VRHADD patterns I noticed
as going through. Although I don't believe NEON would ever
use the patterns (as it would use ADDL and VSHRN instead)
they should ideally be predicated on having MVE instructions.
As with other targets, set the throughput cost of control-flow
instructions to free so that we don't miss out of vectorization
opportunities.
Differential Revision: https://reviews.llvm.org/D85283
Added patterns so that both SSAT and USAT instructions are generated with shifts. Added corresponding regression tests.
Differential Review: https://reviews.llvm.org/D85120
VPSEL has slightly different semantics under tail predication (it can
end up selecting from Qn, Qm and Qd). We do not model that at the moment
so they block tail predicated loops from being formed.
This just converts them into a predicated VMOV instead (via a VORR),
allowing tail predication to happen whilst still modelling the original
behaviour of the input.
Differential Revision: https://reviews.llvm.org/D85110
Fixes a regression caused by D82439, in which IT blocks were no longer being
generated when -Oz is present. This was due to the CPSR register being marked as
dead, while this case was not accounted for.
Differential Revision: https://reviews.llvm.org/D83667
This adds sign/zero extending scalar loads/stores to the MVE
instructions added in D77813, allowing us to create up more post-inc
instructions. These are comparatively simple, compared to LDR/STR (which
may be better turned into an LDRD/LDM), but still require some additions
over MVE instructions. Because there are i12 and i8 variants of the
offset loads/stores dealing with different signs, we may need to convert
an i12 address to a i8 negative instruction. t2LDRBi12 can also be
shrunk to a tLDRi under the right conditions, so we need to be careful
with codesize too.
Differential Revision: https://reviews.llvm.org/D78625
I've been looking at missed vectorizations in one codebase.
One particular thing that stands out is that some of the loops
reach vectorizer in a rather mangled form, with weird PHI's,
and some of the loops aren't even in a rotated form.
After taking a more detailed look, that happened because
the loop's headers were too big by then. It is evident that
SimplifyCFG's common code hoisting transform is at fault there,
because the pattern it handles is precisely the unrotated
loop basic block structure.
Surprizingly, `SimplifyCFGOpt::HoistThenElseCodeToIf()` is enabled
by default, and is always run, unlike it's friend, common code sinking
transform, `SinkCommonCodeFromPredecessors()`, which is not enabled
by default and is only run once very late in the pipeline.
I'm proposing to harmonize this, and disable common code hoisting
until //late// in pipeline. Definition of //late// may vary,
here currently i've picked the same one as for code sinking,
but i suppose we could enable it as soon as right after
loop rotation happens.
Experimentation shows that this does indeed unsurprizingly help,
more loops got rotated, although other issues remain elsewhere.
Now, this undoubtedly seriously shakes phase ordering.
This will undoubtedly be a mixed bag in terms of both compile- and
run- time performance, codesize. Since we no longer aggressively
hoist+deduplicate common code, we don't pay the price of said hoisting
(which wasn't big). That may allow more loops to be rotated,
so we pay that price. That, in turn, that may enable all the transforms
that require canonical (rotated) loop form, including but not limited to
vectorization, so we pay that too. And in general, no deduplication means
more [duplicate] instructions going through the optimizations. But there's still
late hoisting, some of them will be caught late.
As per benchmarks i've run {F12360204}, this is mostly within the noise,
there are some small improvements, some small regressions.
One big regression i saw i fixed in rG8d487668d09fb0e4e54f36207f07c1480ffabbfd, but i'm sure
this will expose many more pre-existing missed optimizations, as usual :S
llvm-compile-time-tracker.com thoughts on this:
http://llvm-compile-time-tracker.com/compare.php?from=e40315d2b4ed1e38962a8f33ff151693ed4ada63&to=c8289c0ecbf235da9fb0e3bc052e3c0d6bff5cf9&stat=instructions
* this does regress compile-time by +0.5% geomean (unsurprizingly)
* size impact varies; for ThinLTO it's actually an improvement
The largest fallout appears to be in GVN's load partial redundancy
elimination, it spends *much* more time in
`MemoryDependenceResults::getNonLocalPointerDependency()`.
Non-local `MemoryDependenceResults` is widely-known to be, uh, costly.
There does not appear to be a proper solution to this issue,
other than silencing the compile-time performance regression
by tuning cut-off thresholds in `MemoryDependenceResults`,
at the cost of potentially regressing run-time performance.
D84609 attempts to move in that direction, but the path is unclear
and is going to take some time.
If we look at stats before/after diffs, some excerpts:
* RawSpeed (the target) {F12360200}
* -14 (-73.68%) loops not rotated due to the header size (yay)
* -272 (-0.67%) `"Number of live out of a loop variables"` - good for vectorizer
* -3937 (-64.19%) common instructions hoisted
* +561 (+0.06%) x86 asm instructions
* -2 basic blocks
* +2418 (+0.11%) IR instructions
* vanilla test-suite + RawSpeed + darktable {F12360201}
* -36396 (-65.29%) common instructions hoisted
* +1676 (+0.02%) x86 asm instructions
* +662 (+0.06%) basic blocks
* +4395 (+0.04%) IR instructions
It is likely to be sub-optimal for when optimizing for code size,
so one might want to change tune pipeline by enabling sinking/hoisting
when optimizing for size.
Reviewed By: mkazantsev
Differential Revision: https://reviews.llvm.org/D84108
This patch uses the feature added in D79162 to fix the cost of a
sext/zext of a masked load, or a trunc for a masked store.
Previously, those were considered cheap or even free, but it's
not the case as we cannot split the load in the same way we would for
normal loads.
This updates the costs to better reflect reality, and adds a test for it
in test/Analysis/CostModel/ARM/cast.ll.
It also adds a vectorizer test that showcases the improvement: in some
cases, the vectorizer will now choose a smaller VF when
tail-predication is enabled, which results in better codegen. (Because
if it were to use a higher VF in those cases, the code we see above
would be generated, and the vmovs would block tail-predication later in
the process, resulting in very poor codegen overall)
Original Patch by Pierre van Houtryve
Differential Revision: https://reviews.llvm.org/D79163
Currently, getCastInstrCost has limited information about the cast it's
rating, often just the opcode and types. Sometimes there is a context
instruction as well, but it isn't trustworthy: for instance, when the
vectorizer is rating a plan, it calls getCastInstrCost with the old
instructions when, in fact, it's trying to evaluate the cost of the
instruction post-vectorization. Thus, the current system can get the
cost of certain casts incorrect as the correct cost can vary greatly
based on the context in which it's used.
For example, if the vectorizer queries getCastInstrCost to evaluate the
cost of a sext(load) with tail predication enabled, getCastInstrCost
will think it's free most of the time, but it's not always free. On ARM
MVE, a VLD2 group cannot be extended like a normal VLDR can. Similar
situations can come up with how masked loads can be extended when being
split.
To fix that, this path adds a new parameter to getCastInstrCost to give
it a hint about the context of the cast. It adds a CastContextHint enum
which contains the type of the load/store being created by the
vectorizer - one for each of the types it can produce.
Original patch by Pierre van Houtryve
Differential Revision: https://reviews.llvm.org/D79162
Optimize some specific immediates selection by materializing them with sub/mvn
instructions as opposed to loading them from the constant pool.
Patch by Ben Shi, powerman1st@163.com.
Differential Revision: https://reviews.llvm.org/D83745
A patch following up on the introduction of pointer induction variables, adding
a preprocessing step to the address optimisation in the MVEGatherScatterLowering
pass. If the getelementpointer that is the address is itself using a
getelementpointer as base, they will be merged into one by summing up the
offsets, after checking that this will not cause an overflow (this can be
repeated recursively).
Differential Revision: https://reviews.llvm.org/D84027
Many Thumb1 instructions are defined to set CPSR if executed outside an IT
block, but leave it alone from inside one. In MachineIR this is represented by
whether an optional register is CPSR or NoReg (0), and affects how the
instructions are printed.
This sets the instruction to the appropriate form during if-conversion.
Added extra patterns to VABD instruction so it is selected in place of VSUB and VABS. Added corresponding regression test too.
Differential Revision: https://reviews.llvm.org/D84500
Similar to 8fa824d7a3 but this time for MLA patterns, this selects
predicated vmlav/vmlava/vmlalv/vmlava instructions from
vecreduce.add(select(p, mul(x, y), 0)) nodes.
Differential Revision: https://reviews.llvm.org/D84102
Nikita Popov