[llvm] [InstCombine] Fold (X == 0 ? Y : 0) | X to X == 0 ? Y : X (PR #138373)
via llvm-commits
llvm-commits at lists.llvm.org
Fri May 2 19:03:58 PDT 2025
https://github.com/YLChenZ created https://github.com/llvm/llvm-project/pull/138373
Closes #137161.
Proof: https://alive2.llvm.org/ce/z/UzdBeu.
>From 6fdcdeadb11c973b07ea1dd58db5b872aa0b394b Mon Sep 17 00:00:00 2001
From: YLChenZ <chentongyongcz at gmail.com>
Date: Sat, 3 May 2025 09:51:12 +0800
Subject: [PATCH] [InstCombine] Fold (X == 0 ? Y : 0) | X to X == 0 ? Y : X
---
.../InstCombine/InstCombineAndOrXor.cpp | 40 +++++
.../InstCombine/or-select-zero-icmp.ll | 144 ++++++++++++++++++
2 files changed, 184 insertions(+)
create mode 100644 llvm/test/Transforms/InstCombine/or-select-zero-icmp.ll
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index f059d87e581fd..77e886c98261c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -3575,6 +3575,41 @@ static Value *foldOrOfInversions(BinaryOperator &I,
return nullptr;
}
+// Optimize patterns where an OR operation combines a select-based zero check
+// with its condition value. This handles both scalar and vector types.
+//
+// Given:
+// (X == 0 ? Y : 0) | X --> X == 0 ? Y : X
+// X | (X == 0 ? Y : 0) --> X == 0 ? Y : X
+//
+// Also handles cases where X might be wrapped in zero/sign extensions.
+static Instruction *foldOrOfSelectZero(BinaryOperator &BO, Value *Op0,
+ Value *Op1) {
+ CmpPredicate Pred;
+ Value *X, *Y;
+
+ // Check both operand orders to handle commutative OR
+ for (Value *SelVal : {Op0, Op1}) {
+ // The other operand in the OR operation (potentially X or extended X)
+ Value *Other = (SelVal == Op0) ? Op1 : Op0;
+
+ // Attempt to match the select pattern:
+ // select(icmp eq X, 0), Y, 0
+ // Where X might be:
+ // - Original value
+ // - Zero extended value (zext)
+ // - Sign extended value (sext)
+ if (match(SelVal, m_Select(m_c_ICmp(Pred, m_Value(X), m_Zero()), m_Value(Y),
+ m_Zero())) &&
+ Pred == ICmpInst::ICMP_EQ &&
+ match(Other, m_ZExtOrSExtOrSelf(m_Specific(X)))) {
+ return SelectInst::Create(cast<SelectInst>(SelVal)->getCondition(), Y,
+ Other);
+ }
+ }
+ return nullptr;
+}
+
// FIXME: We use commutative matchers (m_c_*) for some, but not all, matches
// here. We should standardize that construct where it is needed or choose some
// other way to ensure that commutated variants of patterns are not missed.
@@ -3657,6 +3692,11 @@ Instruction *InstCombinerImpl::visitOr(BinaryOperator &I) {
/*NSW=*/true, /*NUW=*/true))
return R;
}
+
+ // (X == 0 ? Y : 0) | X -> X == 0 ? Y : X
+ // X | (X == 0 ? Y : 0) -> X == 0 ? Y : X
+ if (Instruction *R = foldOrOfSelectZero(I, Op0, Op1))
+ return R;
Value *X, *Y;
const APInt *CV;
diff --git a/llvm/test/Transforms/InstCombine/or-select-zero-icmp.ll b/llvm/test/Transforms/InstCombine/or-select-zero-icmp.ll
new file mode 100644
index 0000000000000..fc6b47f0eeb17
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/or-select-zero-icmp.ll
@@ -0,0 +1,144 @@
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+; Basic functional test
+define i32 @basic(i32 %a, i32 %b) {
+; CHECK-LABEL: @basic(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[A:%.*]], 0
+; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i32 [[B:%.*]], i32 [[A]]
+; CHECK-NEXT: ret i32 [[RES]]
+;
+ %cmp = icmp eq i32 %a, 0
+ %sel = select i1 %cmp, i32 %b, i32 0
+ %or = or i32 %sel, %a
+ ret i32 %or
+}
+
+; Operand order swap test
+define i32 @swap_operand_order(i32 %x, i32 %y) {
+; CHECK-LABEL: @swap_operand_order(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[X:%.*]], 0
+; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i32 [[Y:%.*]], i32 [[X]]
+; CHECK-NEXT: ret i32 [[RES]]
+;
+ %cmp = icmp eq i32 %x, 0
+ %sel = select i1 %cmp, i32 %y, i32 0
+ %or = or i32 %x, %sel
+ ret i32 %or
+}
+
+; Negative test: Non-zero false value in select
+define i32 @negative_non_zero_false_val(i32 %a, i32 %b) {
+; CHECK-LABEL: @negative_non_zero_false_val(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[A:%.*]], 0
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 [[B:%.*]], i32 1
+; CHECK-NEXT: [[OR:%.*]] = or i32 [[SEL]], [[A]]
+; CHECK-NEXT: ret i32 [[OR]]
+;
+ %cmp = icmp eq i32 %a, 0
+ %sel = select i1 %cmp, i32 %b, i32 1
+ %or = or i32 %sel, %a
+ ret i32 %or
+}
+
+; Negative test: Incorrect comparison predicate (NE)
+define i32 @negative_wrong_predicate(i32 %a, i32 %b) {
+; CHECK-LABEL: @negative_wrong_predicate(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[A:%.*]], 0
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 0, i32 [[B:%.*]]
+; CHECK-NEXT: [[OR:%.*]] = or i32 [[SEL]], [[A]]
+; CHECK-NEXT: ret i32 [[OR]]
+;
+ %cmp = icmp ne i32 %a, 0
+ %sel = select i1 %cmp, i32 %b, i32 0
+ %or = or i32 %sel, %a
+ ret i32 %or
+}
+
+; Comparison direction swap test (0 == X)
+define i32 @cmp_swapped(i32 %x, i32 %y) {
+; CHECK-LABEL: @cmp_swapped(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[X:%.*]], 0
+; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i32 [[Y:%.*]], i32 [[X]]
+; CHECK-NEXT: ret i32 [[RES]]
+;
+ %cmp = icmp eq i32 0, %x
+ %sel = select i1 %cmp, i32 %y, i32 0
+ %or = or i32 %x, %sel
+ ret i32 %or
+}
+
+; Complex expression test
+define i32 @complex_expression(i32 %a, i32 %b) {
+; CHECK-LABEL: @complex_expression(
+; CHECK-NEXT: [[X:%.*]] = add i32 [[A:%.*]], 1
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[X]], 0
+; CHECK-NEXT: [[RES:%.*]] = select i1 [[CMP]], i32 [[B:%.*]], i32 [[X]]
+; CHECK-NEXT: ret i32 [[RES]]
+;
+ %x = add i32 %a, 1
+ %cmp = icmp eq i32 %x, 0
+ %sel = select i1 %cmp, i32 %b, i32 0
+ %or = or i32 %sel, %x
+ ret i32 %or
+}
+
+; zext test
+define i32 @zext_cond(i8 %a, i32 %b) {
+; CHECK-LABEL: @zext_cond(
+; CHECK-NEXT: [[Z:%.*]] = zext i8 [[A:%.*]] to i32
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[A]], 0
+; CHECK-NEXT: [[OR:%.*]] = select i1 [[CMP]], i32 [[B:%.*]], i32 [[Z]]
+; CHECK-NEXT: ret i32 [[OR]]
+ %z = zext i8 %a to i32
+ %cmp = icmp eq i32 %z, 0
+ %sel = select i1 %cmp, i32 %b, i32 0
+ %or = or i32 %sel, %z
+ ret i32 %or
+}
+
+; sext test
+define i32 @sext_cond(i8 %a, i32 %b) {
+; CHECK-LABEL: @sext_cond(
+; CHECK-NEXT: [[S:%.*]] = sext i8 [[A:%.*]] to i32
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[A]], 0
+; CHECK-NEXT: [[OR:%.*]] = select i1 [[CMP]], i32 [[B:%.*]], i32 [[S]]
+; CHECK-NEXT: ret i32 [[OR]]
+ %s = sext i8 %a to i32
+ %cmp = icmp eq i32 %s, 0
+ %sel = select i1 %cmp, i32 %b, i32 0
+ %or = or i32 %sel, %s
+ ret i32 %or
+}
+
+; Vector type test
+define <2 x i32> @vector_type(<2 x i32> %a, <2 x i32> %b) {
+; CHECK-LABEL: @vector_type(
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq <2 x i32> [[A:%.*]], zeroinitializer
+; CHECK-NEXT: [[RES:%.*]] = select <2 x i1> [[CMP]], <2 x i32> [[B:%.*]], <2 x i32> [[A]]
+; CHECK-NEXT: ret <2 x i32> [[RES]]
+;
+ %cmp = icmp eq <2 x i32> %a, zeroinitializer
+ %sel = select <2 x i1> %cmp, <2 x i32> %b, <2 x i32> zeroinitializer
+ %or = or <2 x i32> %sel, %a
+ ret <2 x i32> %or
+}
+
+; Pointer type test (should not trigger optimization)
+define i32* @pointer_type(i32* %p, i32* %q) {
+; CHECK-LABEL: @pointer_type(
+; CHECK-NEXT: [[A:%.*]] = ptrtoint ptr [[P:%.*]] to i64
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[P]], null
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], ptr [[Q:%.*]], ptr null
+; CHECK-NEXT: [[SEL_INT:%.*]] = ptrtoint ptr [[SEL]] to i64
+; CHECK-NEXT: [[OR:%.*]] = or i64 [[A]], [[SEL_INT]]
+; CHECK-NEXT: [[RET:%.*]] = inttoptr i64 [[OR]] to ptr
+; CHECK-NEXT: ret ptr [[RET]]
+;
+ %a = ptrtoint i32* %p to i64
+ %cmp = icmp eq i64 %a, 0
+ %sel = select i1 %cmp, i32* %q, i32* null
+ %sel_int = ptrtoint i32* %sel to i64
+ %or_val = or i64 %a, %sel_int
+ %ret = inttoptr i64 %or_val to i32*
+ ret i32* %ret
+}
More information about the llvm-commits
mailing list