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[InstCombine] Enable FAdd simplifications when user can ignore sign bit #157757

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Merged
merged 6 commits into from
Sep 12, 2025
Merged

[InstCombine] Enable FAdd simplifications when user can ignore sign bit #157757

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b230ed7
[InstSimplify] Enable FAdd simplifications when user can ignore sign bit
VedantParanjape Sep 9, 2025
3aaf155
moved opt to IC from InstSimplify
VedantParanjape Sep 10, 2025
717c2c8
revert fcanonicalize testcase
VedantParanjape Sep 10, 2025
486bbe7
rework to check for a single use, and update the testcase
VedantParanjape Sep 11, 2025
9ff60ee
Add support for FSub as well
VedantParanjape Sep 11, 2025
1dd1c85
Update llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
VedantParanjape Sep 12, 2025
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4 changes: 3 additions & 1 deletion llvm/lib/Analysis/InstructionSimplify.cpp
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Expand Up @@ -5710,7 +5710,9 @@ simplifyFAddInst(Value *Op0, Value *Op1, FastMathFlags FMF,
// fadd X, 0 ==> X, when we know X is not -0
if (canIgnoreSNaN(ExBehavior, FMF))
if (match(Op1, m_PosZeroFP()) &&
(FMF.noSignedZeros() || cannotBeNegativeZero(Op0, Q)))
(FMF.noSignedZeros() || cannotBeNegativeZero(Op0, Q) ||
(Q.CxtI && !Q.CxtI->use_empty() &&
canIgnoreSignBitOfZero(*(Q.CxtI->use_begin())))))
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@nikic nikic Sep 10, 2025

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You can't do use-based reasoning inside InstSimplify, this must happen in InstCombine.

return Op0;

if (!isDefaultFPEnvironment(ExBehavior, Rounding))
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5 changes: 2 additions & 3 deletions llvm/test/CodeGen/AMDGPU/fcanonicalize-elimination.ll
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Expand Up @@ -363,9 +363,8 @@ define amdgpu_kernel void @test_no_fold_canonicalize_fcopysign_value_f32(ptr add
}

; GCN-LABEL: test_fold_canonicalize_fabs_value_f32:
; GCN: v_and_b32_e32 [[V:v[0-9]+]], 0x7fffffff, v{{[0-9]+}}
; GCN-NOT: v_mul
; GCN-NOT: v_max
; VI: v_mul_f32_e64 [[V:v[0-9]+]], 1.0, |[[V]]|
; GFX9: v_max_f32_e64 [[V:v[0-9]+]], |[[V]]|, |[[V]]|
; GCN: {{flat|global}}_store_dword v{{.+}}, [[V]]
define amdgpu_kernel void @test_fold_canonicalize_fabs_value_f32(ptr addrspace(1) %arg) {
%id = tail call i32 @llvm.amdgcn.workitem.id.x()
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12 changes: 12 additions & 0 deletions llvm/test/Transforms/InstSimplify/fold-fadd-with-zero-gh154238.ll
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@@ -0,0 +1,12 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt < %s -passes=instsimplify -S | FileCheck %s
define float @src(float %arg1) {
; CHECK-LABEL: define float @src(
; CHECK-SAME: float [[ARG1:%.*]]) {
; CHECK-NEXT: [[V3:%.*]] = call float @llvm.fabs.f32(float [[ARG1]])
; CHECK-NEXT: ret float [[V3]]
;
%v2 = fadd float %arg1, 0.000000e+00
%v3 = call float @llvm.fabs.f32(float %v2)
ret float %v3
}