[llvm-branch-commits] [llvm] InstCombine: SimplifyDemandedFPClass multiple use support for select (PR #175548)
Matt Arsenault via llvm-branch-commits
llvm-branch-commits at lists.llvm.org
Mon Jan 12 06:34:33 PST 2026
https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/175548
None
>From 85c1ce9956e571f08d6af2a2d1a4a5ff9da9a62a Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Mon, 12 Jan 2026 15:19:38 +0100
Subject: [PATCH] InstCombine: SimplifyDemandedFPClass multiple use support for
select
---
.../InstCombineSimplifyDemanded.cpp | 28 ++++++++-
.../InstCombine/simplify-demanded-fpclass.ll | 62 +++++++++++++++++--
2 files changed, 83 insertions(+), 7 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 22064638bb229..9382f5b536d87 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -2766,7 +2766,33 @@ Value *InstCombinerImpl::SimplifyDemandedUseFPClass(Instruction *I,
Value *InstCombinerImpl::SimplifyMultipleUseDemandedFPClass(
Instruction *I, FPClassTest DemandedMask, KnownFPClass &Known,
Instruction *CxtI, unsigned Depth) {
- Known = computeKnownFPClass(I, DemandedMask, CxtI, Depth + 1);
+ switch (I->getOpcode()) {
+ case Instruction::Select: {
+ // TODO: Can we infer which side it came from based on adjusted result
+ // class?
+ KnownFPClass KnownRHS =
+ computeKnownFPClass(I->getOperand(2), DemandedMask, CxtI, Depth + 1);
+ if (KnownRHS.isKnownNever(DemandedMask))
+ return I->getOperand(1);
+
+ KnownFPClass KnownLHS =
+ computeKnownFPClass(I->getOperand(1), DemandedMask, CxtI, Depth + 1);
+ if (KnownLHS.isKnownNever(DemandedMask))
+ return I->getOperand(2);
+
+ const SimplifyQuery &SQ = getSimplifyQuery();
+ adjustKnownFPClassForSelectArm(KnownLHS, I->getOperand(0), I->getOperand(1),
+ /*Invert=*/false, SQ, Depth);
+ adjustKnownFPClassForSelectArm(KnownRHS, I->getOperand(0), I->getOperand(2),
+ /*Invert=*/true, SQ, Depth);
+ Known = KnownLHS.intersectWith(KnownRHS);
+ break;
+ }
+ default:
+ Known = computeKnownFPClass(I, DemandedMask, CxtI, Depth + 1);
+ break;
+ }
+
return getFPClassConstant(I->getType(), DemandedMask & Known.KnownFPClasses);
}
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
index 16378b8677f83..e04fa3c0d6481 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
@@ -383,7 +383,7 @@ define nofpclass(inf) float @ret_nofpclass_inf__select_multi_use_pinf_lhs(i1 %co
; CHECK-SAME: (i1 [[COND:%.*]], float [[X:%.*]], ptr [[PTR:%.*]]) {
; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[COND]], float 0x7FF0000000000000, float [[X]]
; CHECK-NEXT: store float [[SELECT]], ptr [[PTR]], align 4
-; CHECK-NEXT: ret float [[SELECT]]
+; CHECK-NEXT: ret float [[X]]
;
%select = select i1 %cond, float 0x7FF0000000000000, float %x
store float %select, ptr %ptr
@@ -1098,13 +1098,11 @@ define nofpclass(nan inf nzero nsub nnorm) float @test_powr_issue64870_2(float n
; CHECK-LABEL: define nofpclass(nan inf nzero nsub nnorm) float @test_powr_issue64870_2
; CHECK-SAME: (float nofpclass(nan inf) [[ARG:%.*]], float nofpclass(nan inf) [[ARG1:%.*]]) {
; CHECK-NEXT: bb:
-; CHECK-NEXT: [[I:%.*]] = fcmp olt float [[ARG]], 0.000000e+00
-; CHECK-NEXT: [[I2:%.*]] = select i1 [[I]], float 0x7FF8000000000000, float [[ARG]]
-; CHECK-NEXT: [[I3:%.*]] = tail call float @llvm.log2.f32(float noundef [[I2]])
+; CHECK-NEXT: [[I3:%.*]] = tail call float @llvm.log2.f32(float noundef [[ARG]])
; CHECK-NEXT: [[I5:%.*]] = fmul float [[ARG1]], [[I3]]
; CHECK-NEXT: [[I6:%.*]] = tail call noundef nofpclass(ninf nzero nsub nnorm) float @llvm.exp2.f32(float noundef [[I5]])
-; CHECK-NEXT: [[I10:%.*]] = fcmp oeq float [[I2]], 0.000000e+00
-; CHECK-NEXT: [[I12:%.*]] = select i1 [[I10]], float 0.000000e+00, float [[I6]]
+; CHECK-NEXT: [[TMP0:%.*]] = fcmp oeq float [[ARG]], 0.000000e+00
+; CHECK-NEXT: [[I12:%.*]] = select i1 [[TMP0]], float 0.000000e+00, float [[I6]]
; CHECK-NEXT: ret float [[I12]]
;
bb:
@@ -1542,3 +1540,55 @@ define nofpclass(nan) float @exp_select_must_be_0_commute(float %arg, float nofp
%exp = call float @llvm.exp.f32(float %select)
ret float %exp
}
+
+; Select has multiple uses, with the same user
+define nofpclass(nan) float @ret_nonan_fmul_select_fmul_select_nan_multiple_use(i1 %cond, float noundef %x) {
+; CHECK-LABEL: define nofpclass(nan) float @ret_nonan_fmul_select_fmul_select_nan_multiple_use
+; CHECK-SAME: (i1 [[COND:%.*]], float noundef [[X:%.*]]) {
+; CHECK-NEXT: [[FMUL:%.*]] = fmul float [[X]], [[X]]
+; CHECK-NEXT: ret float [[FMUL]]
+;
+ %select = select i1 %cond, float %x, float 0x7FF8000000000000
+ %fmul = fmul float %select, %select
+ ret float %fmul
+}
+
+define nofpclass(nan) float @ret_nonan_fmul_select_fmul_select_nan_multiple_use_commute(i1 %cond, float noundef %x) {
+; CHECK-LABEL: define nofpclass(nan) float @ret_nonan_fmul_select_fmul_select_nan_multiple_use_commute
+; CHECK-SAME: (i1 [[COND:%.*]], float noundef [[X:%.*]]) {
+; CHECK-NEXT: [[FMUL:%.*]] = fmul float [[X]], [[X]]
+; CHECK-NEXT: ret float [[FMUL]]
+;
+ %select = select i1 %cond, float 0x7FF8000000000000, float %x
+ %fmul = fmul float %select, %select
+ ret float %fmul
+}
+
+; Select has a second, unrelated use
+define nofpclass(nan) float @ret_nonan_fmul_select_nan_other_use(i1 %cond, float noundef %x, float %y, ptr %ptr) {
+; CHECK-LABEL: define nofpclass(nan) float @ret_nonan_fmul_select_nan_other_use
+; CHECK-SAME: (i1 [[COND:%.*]], float noundef [[X:%.*]], float [[Y:%.*]], ptr [[PTR:%.*]]) {
+; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[COND]], float [[X]], float 0x7FF8000000000000
+; CHECK-NEXT: store float [[SELECT]], ptr [[PTR]], align 4
+; CHECK-NEXT: [[NAN_USER:%.*]] = fmul float [[X]], [[Y]]
+; CHECK-NEXT: ret float [[NAN_USER]]
+;
+ %select = select i1 %cond, float %x, float 0x7FF8000000000000
+ store float %select, ptr %ptr
+ %nan.user = fmul float %select, %y
+ ret float %nan.user
+}
+
+define nofpclass(nan) float @ret_nonan_fmul_select_nan_other_use_commute(i1 %cond, float noundef %x, float %y, ptr %ptr) {
+; CHECK-LABEL: define nofpclass(nan) float @ret_nonan_fmul_select_nan_other_use_commute
+; CHECK-SAME: (i1 [[COND:%.*]], float noundef [[X:%.*]], float [[Y:%.*]], ptr [[PTR:%.*]]) {
+; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[COND]], float 0x7FF8000000000000, float [[X]]
+; CHECK-NEXT: store float [[SELECT]], ptr [[PTR]], align 4
+; CHECK-NEXT: [[NAN_USER:%.*]] = fmul float [[X]], [[Y]]
+; CHECK-NEXT: ret float [[NAN_USER]]
+;
+ %select = select i1 %cond, float 0x7FF8000000000000, float %x
+ store float %select, ptr %ptr
+ %nan.user = fmul float %select, %y
+ ret float %nan.user
+}
More information about the llvm-branch-commits
mailing list