All of the code that handles general constant here (other than the more
restrictive APInt-dealing code) expects that it is an immediate,
because otherwise we won't actually fold the constants, and increase
instruction count. And it isn't obvious why we'd be okay with
increasing the number of constant expressions,
those still will have to be run..
But after 2829094a8e
this could also cause endless combine loops.
So actually properly restrict this code to immediates.
This reverts commit a547b4e26b,
relanding commit 31d219d299,
which was reverted because there was a conflicting inverse transform,
which was causing an endless combine loop, which has now been adjusted.
Original commit message:
https://alive2.llvm.org/ce/z/67w-wQ
We prefer `add`s over `sub`, and this particular xform
allows further folds to happen:
Fixes https://bugs.llvm.org/show_bug.cgi?id=49858
I.e., if any/all of the consants is an expression, don't do it.
Since those constants won't reduce into an immediate,
but would be left as an constant expression, they could cause
endless combine loops after 31d219d299
added an inverse transformation.
We determined that the MSVC implementation of std::aligned* isn't suited
to our needs. It doesn't support 16 byte alignment or higher, and it
doesn't really guarantee 8 byte alignment. See
https://github.com/microsoft/STL/issues/1533
Also reverts "ADT: Change AlignedCharArrayUnion to an alias of std::aligned_union_t, NFC"
Also reverts "ADT: Remove AlignedCharArrayUnion, NFC" to bring back
AlignedCharArrayUnion.
This reverts commit 4d8bf870a8.
This reverts commit d10f9863a5.
This reverts commit 4b5dc150b9.
Prepare to delete `AlignedCharArrayUnion` by migrating its users over to
`std::aligned_union_t`.
I will delete `AlignedCharArrayUnion` and its tests in a follow-up
commit so that it's easier to revert in isolation in case some
downstream wants to keep using it.
Differential Revision: https://reviews.llvm.org/D92516
Update all the users of `AlignedCharArrayUnion` to stop peeking inside
(to look at `buffer`) so that a follow-up patch can replace it with an
alias to `std::aligned_union_t`.
This was reviewed as part of https://reviews.llvm.org/D92512, but I'm
splitting this bit out to commit first to reduce churn in case the
change to `AlignedCharArrayUnion` needs to be reverted for some
unexpected reason.
We need to preserve wrapping flags to allow better folds.
The cases with geps may be non-intuitive, but that appears to agree with Alive2:
https://alive2.llvm.org/ce/z/JQcqw7
We create 'nsw' ops independent from the original wrapping on the sub.
This is a retry of 324a53205. I cautiously reverted that at 6aa3fc4
because the rules about gep math were not clear. Since then, we
have added this line to LangRef for gep inbounds:
"The successive addition of offsets (without adding the base address)
does not wrap the pointer index type in a signed sense (nsw)."
See D90708 and post-commit comments on the revert patch for more details.
Handle the emission of the add in a single place, instead of three
different ones.
Don't emit an unnecessary add with zero to start with. It will get
dropped by InstCombine, but we may as well not create it in the
first place. This also means that InstCombine does not need to
specially handle this extra add.
This is conceptually NFC, but can affect worklist order etc.
There might be some demanded/known bits way to generalize this,
but I'm not seeing it right now.
This came up as a regression when I was looking at a different
demanded bits improvement.
https://rise4fun.com/Alive/5fl
Name: general
Pre: ((-1 << countTrailingZeros(C1)) & C2) == 0
%a1 = add i8 %x, C1
%a2 = and i8 %x, C2
%r = sub i8 %a1, %a2
=>
%r = and i8 %a1, ~C2
Name: test 1
%a1 = add i8 %x, 192
%a2 = and i8 %x, 10
%r = sub i8 %a1, %a2
=>
%r = and i8 %a1, -11
Name: test 2
%a1 = add i8 %x, -108
%a2 = and i8 %x, 3
%r = sub i8 %a1, %a2
=>
%r = and i8 %a1, -4
As shown in the affected test, we could increase instruction
count without this limitation. There's another test with extra
use that shows we still convert directly to a real "sext" if
possible.
There might be a better way to specify the pre-conditions,
but this is hopefully clearer than the way it was written:
https://rise4fun.com/Alive/Jhk3
Pre: C2 < 0 && isShiftedMask(C2) && (C1 == C1 & C2)
%a = and %x, C2
%r = add %a, C1
=>
%a2 = add %x, C1
%r = and %a2, C2
Pre-conditions seem to be optimal, but we don't need a use check
because we are only replacing an add with a sub.
https://rise4fun.com/Alive/hzN
Pre: (~C1 | C2 == -1) && isPowerOf2(C2+1)
%m = and i8 %x, C1
%f = xor i8 %m, C2
%r = add i8 %f, C3
=>
%r = sub i8 C2 + C3, %m
We do similar factorization folds in SimplifyUsingDistributiveLaws,
but that drops no-wrap properties. Propagating those optimally may
help solve:
https://llvm.org/PR47430
The propagation is all-or-nothing for these patterns: when all
3 incoming ops have nsw or nuw, the 2 new ops should have the
same no-wrap property:
https://alive2.llvm.org/ce/z/Dv8wsU
This also solves:
https://llvm.org/PR47584
This was supposed to be an NFC cleanup, but there's
a real logic difference (did not drop 'nsw') visible
in some tests in addition to an efficiency improvement.
This is because in the case where we have 2 GEPs,
the code was *always* swapping the operands and
negating the result. But if we have 2 GEPs, we
should *never* need swapping/negation AFAICT.
This is part of improving flags propagation noticed
with PR47430.
For a long time, the InstCombine pass handled target specific
intrinsics. Having target specific code in general passes was noted as
an area for improvement for a long time.
D81728 moves most target specific code out of the InstCombine pass.
Applying the target specific combinations in an extra pass would
probably result in inferior optimizations compared to the current
fixed-point iteration, therefore the InstCombine pass resorts to newly
introduced functions in the TargetTransformInfo when it encounters
unknown intrinsics.
The patch should not have any effect on generated code (under the
assumption that code never uses intrinsics from a foreign target).
This introduces three new functions:
TargetTransformInfo::instCombineIntrinsic
TargetTransformInfo::simplifyDemandedUseBitsIntrinsic
TargetTransformInfo::simplifyDemandedVectorEltsIntrinsic
A few target specific parts are left in the InstCombine folder, where
it makes sense to share code. The largest left-over part in
InstCombineCalls.cpp is the code shared between arm and aarch64.
This allows to move about 3000 lines out from InstCombine to the targets.
Differential Revision: https://reviews.llvm.org/D81728
This is the integer sibling to D81491.
(a[0] + a[1] + a[2] + a[3]) - (b[0] + b[1] + b[2] +b[3]) -->
(a[0] - b[0]) + (a[1] - b[1]) + (a[2] - b[2]) + (a[3] - b[3])
Removing the "experimental" from these intrinsics is likely
not too far away.
(a[0] + a[1] + a[2] + a[3]) - (b[0] + b[1] + b[2] +b[3]) -->
(a[0] - b[0]) + (a[1] - b[1]) + (a[2] - b[2]) + (a[3] - b[3])
This should be the last step in solving PR43953:
https://bugs.llvm.org/show_bug.cgi?id=43953
We started emitting reduction intrinsics with:
D80867/ rGe50059f6b6b3
So it's a relatively easy pattern match now to re-order those ops.
Also, I have not seen any complaints for the switch to intrinsics
yet, so I'll propose to remove the "experimental" tag from the
intrinsics soon.
Differential Revision: https://reviews.llvm.org/D81491
Summary:
"X % C == 0" is optimized to "X & C-1 == 0" (where C is a power-of-two)
However, "X % Y" can also be represented as "X - (X / Y) * Y" so if I rewrite the initial expression:
"X - (X / C) * C == 0" it's not currently optimized to "X & C-1 == 0", see godbolt: https://godbolt.org/z/KzuXUj
This is my first contribution to LLVM so I hope I didn't mess things up
Reviewers: lebedev.ri, spatel
Reviewed By: lebedev.ri
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D79369
The -reassociate pass tends to transform this kind of pattern into
something that is worse for vectorization and codegen. See PR43953:
https://bugs.llvm.org/show_bug.cgi?id=43953
Follows-up the FP version of the same transform:
rGa0ce2338a083
The -reassociate pass tends to transform this kind of pattern into
something that is worse for vectorization and codegen. See PR43953:
https://bugs.llvm.org/show_bug.cgi?id=43953
This eliminates a use of 'B', so it can enable follow-on transforms
as well as improve analysis/codegen.
The PhaseOrdering test was added for D61726, and that shows
the limits of instcombine vs. real reassociation. We would
need to run some form of CSE to collapse that further.
The intermediate variable naming here is intentional because
there's a test at llvm/test/Bitcode/value-with-long-name.ll
that would break with the usual nameless value. I'm not sure
how to improve that test to be more robust.
The naming may also be helpful to debug regressions if this
change exposes weaknesses in the reassociation pass for example.
Summary:
As we have discussed previously (e.g. in D63992 / D64090 / [[ https://bugs.llvm.org/show_bug.cgi?id=42457 | PR42457 ]]), `sub` instruction
can almost be considered non-canonical. While we do convert `sub %x, C` -> `add %x, -C`,
we sparsely do that for non-constants. But we should.
Here, i propose to interpret `sub %x, %y` as `add (sub 0, %y), %x` IFF the negation can be sinked into the `%y`
This has some potential to cause endless combine loops (either around PHI's, or if there are some opposite transforms).
For former there's `-instcombine-negator-max-depth` option to mitigate it, should this expose any such issues
For latter, if there are still any such opposing folds, we'd need to remove the colliding fold.
In any case, reproducers welcomed!
Reviewers: spatel, nikic, efriedma, xbolva00
Reviewed By: spatel
Subscribers: xbolva00, mgorny, hiraditya, reames, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D68408
Now compiler defines 5 sets of constants to represent rounding mode.
These are:
1. `llvm::APFloatBase::roundingMode`. It specifies all 5 rounding modes
defined by IEEE-754 and is used in `APFloat` implementation.
2. `clang::LangOptions::FPRoundingModeKind`. It specifies 4 of 5 IEEE-754
rounding modes and a special value for dynamic rounding mode. It is used
in clang frontend.
3. `llvm::fp::RoundingMode`. Defines the same values as
`clang::LangOptions::FPRoundingModeKind` but in different order. It is
used to specify rounding mode in in IR and functions that operate IR.
4. Rounding mode representation used by `FLT_ROUNDS` (C11, 5.2.4.2.2p7).
Besides constants for rounding mode it also uses a special value to
indicate error. It is convenient to use in intrinsic functions, as it
represents platform-independent representation for rounding mode. In this
role it is used in some pending patches.
5. Values like `FE_DOWNWARD` and other, which specify rounding mode in
library calls `fesetround` and `fegetround`. Often they represent bits
of some control register, so they are target-dependent. The same names
(not values) and a special name `FE_DYNAMIC` are used in
`#pragma STDC FENV_ROUND`.
The first 4 sets of constants are target independent and could have the
same numerical representation. It would simplify conversion between the
representations. Also now `clang::LangOptions::FPRoundingModeKind` and
`llvm::fp::RoundingMode` do not contain the value for IEEE-754 rounding
direction `roundTiesToAway`, although it is supported natively on
some targets.
This change defines all the rounding mode type via one `llvm::RoundingMode`,
which also contains rounding mode for IEEE rounding direction `roundTiesToAway`.
Differential Revision: https://reviews.llvm.org/D77379
Summary: Rewrite the fsub-0.0 idiom to fneg and always emit fneg for fp
negation. This also extends the scalarization cost in instcombine for unary
operators to result in the same IR rewrites for fneg as for the idiom.
Reviewed By: cameron.mcinally
Differential Revision: https://reviews.llvm.org/D75467
SimplifyAddWithRemainder currently also matches for vector types, but
tries to create an integer constant, which causes a crash.
By using Constant::getIntegerValue() we can support both the scalar and
vector cases.
The 2 added test cases crash without the fix.
Reviewers: spatel, lebedev.ri
Reviewed By: spatel, lebedev.ri
Differential Revision: https://reviews.llvm.org/D75906
Use UnaryOperator::CreateFNeg instead.
Summary:
With the introduction of the native fneg instruction, the
fsub -0.0, %x idiom is obsolete. This patch makes LLVM
emit fneg instead of the idiom in all places.
Reviewed By: cameron.mcinally
Differential Revision: https://reviews.llvm.org/D75130
This is a followup to D73803, which uses the replaceOperand()
helper in more places.
This should be NFC apart from changes to worklist order.
Differential Revision: https://reviews.llvm.org/D73919
Followup to D72978. This moves existing negation handling in
InstCombine into freelyNegateValue(), which make it composable.
In particular, root negations of div/zext/sext/ashr/lshr/sub can
now always be performed through a shl/trunc as well.
Differential Revision: https://reviews.llvm.org/D73288
Fixes https://bugs.llvm.org/show_bug.cgi?id=44529. We already have
a combine to sink a negation through a left-shift, but it currently
only works if the shift operand is negatable without creating any
instructions. This patch introduces freelyNegateValue() as a more
powerful extension of dyn_castNegVal(), which allows negating a
value as long as this doesn't end up increasing instruction count.
Specifically, this patch adds support for negating A-B to B-A.
This mechanism could in the future be extended to handle general
negation chains that a) start at a proper 0-X negation and b) only
require one operand to be freely negatable. This would end up as a
weaker form of D68408 aimed at the most obviously profitable subset
that eliminates a negation entirely.
Differential Revision: https://reviews.llvm.org/D72978
Roman Lebedev