[llvm] [InstCombine] foldOpIntoPhi should apply to icmp with non-constant operand (PR #147676)
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Wed Jul 9 02:03:11 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Ross Kirsling (rkirsling)
<details>
<summary>Changes</summary>
Alive2: https://alive2.llvm.org/ce/z/4MeCzA
Fixes #<!-- -->146263.
---
Full diff: https://github.com/llvm/llvm-project/pull/147676.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp (+4-4)
- (added) llvm/test/Transforms/InstCombine/fold-icmp-without-constant-into-phi.ll (+98)
``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index c6f317a668cfe..e753af73886f3 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -4305,10 +4305,6 @@ Instruction *InstCombinerImpl::foldICmpInstWithConstantNotInt(ICmpInst &I) {
return nullptr;
switch (LHSI->getOpcode()) {
- case Instruction::PHI:
- if (Instruction *NV = foldOpIntoPhi(I, cast<PHINode>(LHSI)))
- return NV;
- break;
case Instruction::IntToPtr:
// icmp pred inttoptr(X), null -> icmp pred X, 0
if (RHSC->isNullValue() &&
@@ -7699,6 +7695,10 @@ Instruction *InstCombinerImpl::visitICmpInst(ICmpInst &I) {
if (Instruction *New = foldSignBitTest(I))
return New;
+ if (auto *PN = dyn_cast<PHINode>(Op0))
+ if (Instruction *NV = foldOpIntoPhi(I, PN))
+ return NV;
+
if (Instruction *Res = foldICmpInstWithConstantNotInt(I))
return Res;
diff --git a/llvm/test/Transforms/InstCombine/fold-icmp-without-constant-into-phi.ll b/llvm/test/Transforms/InstCombine/fold-icmp-without-constant-into-phi.ll
new file mode 100644
index 0000000000000..7c0c1a39d00f7
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/fold-icmp-without-constant-into-phi.ll
@@ -0,0 +1,98 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define i1 @test(i1 %cond, i64 %left, i64 %right) {
+; CHECK-LABEL: define i1 @test(
+; CHECK-SAME: i1 [[COND:%.*]], i64 [[LEFT:%.*]], i64 [[RIGHT:%.*]]) {
+; CHECK-NEXT: [[START:.*:]]
+; CHECK-NEXT: br i1 [[COND]], label %[[COND_TRUE:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_TRUE]]:
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i64 [[RIGHT]], [[LEFT]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[END:.*]], label %[[COND_FALSE]]
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: br label %[[END]]
+; CHECK: [[END]]:
+; CHECK-NEXT: ret i1 false
+;
+start:
+ br i1 %cond, label %cond.true, label %cond.false
+
+cond.true:
+ %cmp = icmp sgt i64 %right, %left
+ br i1 %cmp, label %end, label %cond.false
+
+cond.false:
+ %left_or_right = phi i64 [ %left, %start ], [ %right, %cond.true ]
+ %false = icmp sgt i64 %left_or_right, %left
+ br label %end
+
+end:
+ %result = phi i1 [ false, %cond.true ], [ %false, %cond.false ]
+ ret i1 %result
+}
+
+define i1 @test_with_wrong_icmp(i1 %cond, i64 %left, i64 %right) {
+; CHECK-LABEL: define i1 @test_with_wrong_icmp(
+; CHECK-SAME: i1 [[COND:%.*]], i64 [[LEFT:%.*]], i64 [[RIGHT:%.*]]) {
+; CHECK-NEXT: [[START:.*]]:
+; CHECK-NEXT: br i1 [[COND]], label %[[COND_TRUE:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_TRUE]]:
+; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i64 [[RIGHT]], [[LEFT]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[END:.*]], label %[[COND_FALSE]]
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[LEFT_OR_RIGHT:%.*]] = phi i64 [ [[LEFT]], %[[START]] ], [ [[RIGHT]], %[[COND_TRUE]] ]
+; CHECK-NEXT: [[FALSE:%.*]] = icmp sge i64 [[LEFT_OR_RIGHT]], [[LEFT]]
+; CHECK-NEXT: br label %[[END]]
+; CHECK: [[END]]:
+; CHECK-NEXT: [[RESULT:%.*]] = phi i1 [ false, %[[COND_TRUE]] ], [ [[FALSE]], %[[COND_FALSE]] ]
+; CHECK-NEXT: ret i1 [[RESULT]]
+;
+start:
+ br i1 %cond, label %cond.true, label %cond.false
+
+cond.true:
+ %cmp = icmp sgt i64 %right, %left
+ br i1 %cmp, label %end, label %cond.false
+
+cond.false:
+ %left_or_right = phi i64 [ %left, %start ], [ %right, %cond.true ]
+ %false = icmp sge i64 %left_or_right, %left
+ br label %end
+
+end:
+ %result = phi i1 [ false, %cond.true ], [ %false, %cond.false ]
+ ret i1 %result
+}
+
+define i1 @test_with_unfoldable_phi(i1 %cond, i64 %left, i64 %right) {
+; CHECK-LABEL: define i1 @test_with_unfoldable_phi(
+; CHECK-SAME: i1 [[COND:%.*]], i64 [[LEFT:%.*]], i64 [[RIGHT:%.*]]) {
+; CHECK-NEXT: [[START:.*]]:
+; CHECK-NEXT: br i1 [[COND]], label %[[COND_TRUE:.*]], label %[[COND_FALSE:.*]]
+; CHECK: [[COND_TRUE]]:
+; CHECK-NEXT: [[CMP:%.*]] = icmp slt i64 [[RIGHT]], [[LEFT]]
+; CHECK-NEXT: br i1 [[CMP]], label %[[END:.*]], label %[[COND_FALSE]]
+; CHECK: [[COND_FALSE]]:
+; CHECK-NEXT: [[LEFT_OR_RIGHT:%.*]] = phi i64 [ [[LEFT]], %[[START]] ], [ [[RIGHT]], %[[COND_TRUE]] ]
+; CHECK-NEXT: [[FALSE:%.*]] = icmp sgt i64 [[LEFT_OR_RIGHT]], [[LEFT]]
+; CHECK-NEXT: br label %[[END]]
+; CHECK: [[END]]:
+; CHECK-NEXT: [[RESULT:%.*]] = phi i1 [ false, %[[COND_TRUE]] ], [ [[FALSE]], %[[COND_FALSE]] ]
+; CHECK-NEXT: ret i1 [[RESULT]]
+;
+start:
+ br i1 %cond, label %cond.true, label %cond.false
+
+cond.true:
+ %cmp = icmp slt i64 %right, %left ; slt instead of sgt here
+ br i1 %cmp, label %end, label %cond.false
+
+cond.false:
+ %left_or_right = phi i64 [ %left, %start ], [ %right, %cond.true ]
+ %false = icmp sgt i64 %left_or_right, %left
+ br label %end
+
+end:
+ %result = phi i1 [ false, %cond.true ], [ %false, %cond.false ]
+ ret i1 %result
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/147676
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