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[InstCombine] foldOpIntoPhi should apply to icmp with non-constant operand #147676

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[InstCombine] foldOpIntoPhi should apply to icmp with non-constant operand #147676

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c639d1c
[InstCombine] foldOpIntoPhi should apply to icmp with non-constant op…
rkirsling Jul 9, 2025
a95585b
Address feedback.
rkirsling Jul 9, 2025
f332d8a
Fix a silly typo.
rkirsling Jul 9, 2025
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11 changes: 7 additions & 4 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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() &&
Expand Down Expand Up @@ -7699,6 +7695,13 @@ 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 (auto *PN = dyn_cast<PHINode>(Op1))
if (Instruction *NV = foldOpIntoPhi(I, PN))
return NV;

if (Instruction *Res = foldICmpInstWithConstantNotInt(I))
return Res;

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159 changes: 159 additions & 0 deletions llvm/test/Transforms/InstCombine/fold-icmp-without-constant-into-phi.ll
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@@ -0,0 +1,159 @@
; 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_commuted(i1 %cond, i64 %left, i64 %right) {
; CHECK-LABEL: define i1 @test_commuted(
; 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 slt i64 %left, %left_or_right
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
}

define i1 @test_which_optimizes_to_select(i1 %cond, i64 %left, i64 %right) {
; CHECK-LABEL: define i1 @test_which_optimizes_to_select(
; 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_NOT:%.*]] = icmp sgt i64 [[RIGHT]], [[LEFT]]
; CHECK-NEXT: br i1 [[CMP_NOT]], label %[[COND_FALSE]], label %[[END:.*]]
; CHECK: [[COND_FALSE]]:
; CHECK-NEXT: br label %[[END]]
; CHECK: [[END]]:
; CHECK-NEXT: [[RESULT:%.*]] = phi i1 [ false, %[[COND_TRUE]] ], [ [[COND]], %[[COND_FALSE]] ]
; CHECK-NEXT: ret i1 [[RESULT]]
;
start:
br i1 %cond, label %cond.true, label %cond.false

cond.true:
%cmp = icmp sle 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
}