[llvm] [InstCombine] Enable select freeze poison folding when storing value (PR #129776)
John McIver via llvm-commits
llvm-commits at lists.llvm.org
Wed Mar 12 22:57:20 PDT 2025
https://github.com/jmciver updated https://github.com/llvm/llvm-project/pull/129776
>From cd63f3a87c51d7330d3c7d0170d8f047e760c643 Mon Sep 17 00:00:00 2001
From: John McIver <john.mciver.iii at gmail.com>
Date: Tue, 4 Mar 2025 14:10:38 -0700
Subject: [PATCH] [InstCombine] Enable select freeze poison folding when
storing value
The non-freeze poison argument to select can be one of the following: global,
constant, and noundef arguments.
Alive2 test validation:
- https://alive2.llvm.org/ce/z/jbtCS6
- https://alive2.llvm.org/ce/z/YFA-5S
---
.../InstCombine/InstructionCombining.cpp | 26 +++++-
llvm/test/Transforms/InstCombine/select.ll | 87 +++++++++++++++++--
2 files changed, 104 insertions(+), 9 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 4c14dcfb4d75f..9af201f24d97d 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -4812,7 +4812,7 @@ Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
//
// TODO: This could use getBinopAbsorber() / getBinopIdentity() to avoid
// duplicating logic for binops at least.
- auto getUndefReplacement = [&I](Type *Ty) {
+ auto getConstantReplacement = [&I](Type *Ty) {
Constant *BestValue = nullptr;
Constant *NullValue = Constant::getNullValue(Ty);
for (const auto *U : I.users()) {
@@ -4831,18 +4831,38 @@ Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
return BestValue;
};
+ auto getValueReplacement = [&I, &AC = this->AC, &DT = this->DT]() -> Value * {
+ Value *BestValue = nullptr;
+ for (const auto *U : I.users()) {
+ Value *C = nullptr;
+ Value *SelectArgument = nullptr;
+ if (match(U, m_c_Select(m_Specific(&I), m_Value(SelectArgument))) &&
+ isGuaranteedNotToBeUndefOrPoison(SelectArgument, &AC, &I, &DT))
+ C = SelectArgument;
+
+ if (!BestValue)
+ BestValue = C;
+ else if (BestValue != C)
+ return nullptr;
+ }
+ return BestValue;
+ };
+
if (match(Op0, m_Undef())) {
// Don't fold freeze(undef/poison) if it's used as a vector operand in
// a shuffle. This may improve codegen for shuffles that allow
// unspecified inputs.
if (isUsedWithinShuffleVector(&I))
return nullptr;
- return replaceInstUsesWith(I, getUndefReplacement(I.getType()));
+ if (auto *Replace = getValueReplacement())
+ return replaceInstUsesWith(I, Replace);
+ else
+ return replaceInstUsesWith(I, getConstantReplacement(I.getType()));
}
Constant *C;
if (match(Op0, m_Constant(C)) && C->containsUndefOrPoisonElement()) {
- Constant *ReplaceC = getUndefReplacement(I.getType()->getScalarType());
+ Constant *ReplaceC = getConstantReplacement(I.getType()->getScalarType());
return replaceInstUsesWith(I, Constant::replaceUndefsWith(C, ReplaceC));
}
diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index cc25f4ce24d9a..ebe039f73f375 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -4904,8 +4904,7 @@ define i32 @src_simplify_2x_at_once_and(i32 %x, i32 %y) {
define void @select_freeze_poison_parameter(ptr noundef %addr.src, ptr %addr.tgt, i1 %cond) {
; CHECK-LABEL: @select_freeze_poison_parameter(
-; CHECK-NEXT: [[ADDR_SRC:%.*]] = select i1 [[COND:%.*]], ptr [[ADDR_SRC1:%.*]], ptr null
-; CHECK-NEXT: store ptr [[ADDR_SRC]], ptr [[ADDR_TGT:%.*]], align 8
+; CHECK-NEXT: store ptr [[ADDR_SRC:%.*]], ptr [[ADDR_TGT:%.*]], align 8
; CHECK-NEXT: ret void
;
%freeze = freeze ptr poison
@@ -4914,12 +4913,36 @@ define void @select_freeze_poison_parameter(ptr noundef %addr.src, ptr %addr.tgt
ret void
}
+define i8 @select_freeze_poison_different_parameters(i8 noundef %x, i8 noundef %y, i1 %cond1, i1 %cond2) {
+; CHECK-LABEL: @select_freeze_poison_different_parameters(
+; CHECK-NEXT: [[SEL1:%.*]] = select i1 [[COND1:%.*]], i8 [[X:%.*]], i8 0
+; CHECK-NEXT: [[SEL2:%.*]] = select i1 [[COND2:%.*]], i8 [[Y:%.*]], i8 0
+; CHECK-NEXT: [[CONJ:%.*]] = and i8 [[SEL1]], [[SEL2]]
+; CHECK-NEXT: ret i8 [[CONJ]]
+;
+ %freeze = freeze i8 poison
+ %sel1 = select i1 %cond1, i8 %x, i8 %freeze
+ %sel2 = select i1 %cond2, i8 %y, i8 %freeze
+ %conj = and i8 %sel1, %sel2
+ ret i8 %conj
+}
+
+define i8 @selects_freeze_poison_parameter(i8 noundef %x, i1 %cond1, i1 %cond2) {
+; CHECK-LABEL: @selects_freeze_poison_parameter(
+; CHECK-NEXT: ret i8 [[X:%.*]]
+;
+ %freeze = freeze i8 poison
+ %sel1 = select i1 %cond1, i8 %x, i8 %freeze
+ %sel2 = select i1 %cond2, i8 %x, i8 %freeze
+ %conj = and i8 %sel1, %sel2
+ ret i8 %conj
+}
+
@glb = global ptr null
define void @select_freeze_poison_global(ptr %addr.tgt, i1 %cond) {
; CHECK-LABEL: @select_freeze_poison_global(
-; CHECK-NEXT: [[SELECT_ADDR:%.*]] = select i1 [[COND:%.*]], ptr @glb, ptr null
-; CHECK-NEXT: store ptr [[SELECT_ADDR]], ptr [[ADDR_TGT:%.*]], align 8
+; CHECK-NEXT: store ptr @glb, ptr [[ADDR_TGT:%.*]], align 8
; CHECK-NEXT: ret void
;
%freeze = freeze ptr poison
@@ -4930,8 +4953,7 @@ define void @select_freeze_poison_global(ptr %addr.tgt, i1 %cond) {
define void @select_freeze_poison_constant(ptr %addr.tgt, i1 %cond) {
; CHECK-LABEL: @select_freeze_poison_constant(
-; CHECK-NEXT: [[SELECT_ADDR:%.*]] = select i1 [[COND:%.*]], i32 72, i32 0
-; CHECK-NEXT: store i32 [[SELECT_ADDR]], ptr [[ADDR_TGT:%.*]], align 4
+; CHECK-NEXT: store i32 72, ptr [[ADDR_TGT:%.*]], align 4
; CHECK-NEXT: ret void
;
%freeze = freeze i32 poison
@@ -4939,3 +4961,56 @@ define void @select_freeze_poison_constant(ptr %addr.tgt, i1 %cond) {
store i32 %select.addr, ptr %addr.tgt
ret void
}
+
+define <2 x i8> @select_freeze_poison_mask_vector(i1 %cond, <2 x i8> noundef %y) {
+; CHECK-LABEL: @select_freeze_poison_mask_vector(
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND:%.*]], <2 x i8> [[Y:%.*]], <2 x i8> zeroinitializer
+; CHECK-NEXT: ret <2 x i8> [[SEL]]
+;
+ %freeze = freeze <2 x i8> <i8 0, i8 poison>
+ %sel = select i1 %cond, <2 x i8> %y, <2 x i8> %freeze
+ ret <2 x i8> %sel
+}
+
+define <2 x i8> @selects_freeze_poison_mask_vector(<2 x i8> noundef %x, i1 %cond1, i1 %cond2) {
+; CHECK-LABEL: @selects_freeze_poison_mask_vector(
+; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[COND1:%.*]], i1 [[COND2:%.*]], i1 false
+; CHECK-NEXT: [[X:%.*]] = select i1 [[TMP1]], <2 x i8> [[X1:%.*]], <2 x i8> zeroinitializer
+; CHECK-NEXT: ret <2 x i8> [[X]]
+;
+ %freeze = freeze <2 x i8> <i8 0, i8 poison>
+ %sel1 = select i1 %cond1, <2 x i8> %x, <2 x i8> %freeze
+ %sel2 = select i1 %cond2, <2 x i8> %x, <2 x i8> %freeze
+ %conj = and <2 x i8> %sel1, %sel2
+ ret <2 x i8> %conj
+}
+
+define <2 x i8> @select_freeze_poison_splat_vector(i1 %cond, <2 x i8> noundef %y) {
+; CHECK-LABEL: @select_freeze_poison_splat_vector(
+; CHECK-NEXT: ret <2 x i8> [[Y:%.*]]
+;
+ %freeze = freeze <2 x i8> <i8 poison, i8 poison>
+ %sel = select i1 %cond, <2 x i8> %y, <2 x i8> %freeze
+ ret <2 x i8> %sel
+}
+
+define <2 x i8> @selects_freeze_poison_splat_vector(<2 x i8> noundef %x, i1 %cond1, i1 %cond2) {
+; CHECK-LABEL: @selects_freeze_poison_splat_vector(
+; CHECK-NEXT: ret <2 x i8> [[X:%.*]]
+;
+ %freeze = freeze <2 x i8> <i8 poison, i8 poison>
+ %sel1 = select i1 %cond1, <2 x i8> %x, <2 x i8> %freeze
+ %sel2 = select i1 %cond2, <2 x i8> %x, <2 x i8> %freeze
+ %conj = and <2 x i8> %sel1, %sel2
+ ret <2 x i8> %conj
+}
+
+define <2 x i8> @select_freeze_constant_vector(i1 %cond, <2 x i8> noundef %y) {
+; CHECK-LABEL: @select_freeze_constant_vector(
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[COND:%.*]], <2 x i8> [[Y:%.*]], <2 x i8> zeroinitializer
+; CHECK-NEXT: ret <2 x i8> [[SEL]]
+;
+ %freeze = freeze <2 x i8> <i8 0, i8 0>
+ %sel = select i1 %cond, <2 x i8> %y, <2 x i8> %freeze
+ ret <2 x i8> %sel
+}
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