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[CodeGenPrepare] Bail out of usubo creation if sub's parent is not the same as the comparison #160358

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Merged
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Sep 25, 2025
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[CodeGenPrepare] Bail out of usubo creation if sub's parent is not the same as the comparison #160358

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6 changes: 6 additions & 0 deletions llvm/lib/CodeGen/CodeGenPrepare.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1749,6 +1749,12 @@ bool CodeGenPrepare::combineToUSubWithOverflow(CmpInst *Cmp,
Sub->hasNUsesOrMore(1)))
return false;

// We don't want to move around uses of condition values this late, so we
// check if it is legal to create the call to the intrinsic in the basic
// block containing the icmp.
if (Sub->getParent() != Cmp->getParent() && !Sub->hasOneUse())
return false;

if (!replaceMathCmpWithIntrinsic(Sub, Sub->getOperand(0), Sub->getOperand(1),
Cmp, Intrinsic::usub_with_overflow))
return false;
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10 changes: 5 additions & 5 deletions llvm/test/CodeGen/X86/usub_inc_iv.ll
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Expand Up @@ -303,14 +303,14 @@ define i32 @test_06(ptr %p, i64 %len, i32 %x) {
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i64 [ [[MATH:%.*]], [[BACKEDGE:%.*]] ], [ [[LEN:%.*]], [[ENTRY:%.*]] ]
; CHECK-NEXT: [[TMP0:%.*]] = call { i64, i1 } @llvm.usub.with.overflow.i64(i64 [[IV]], i64 1)
; CHECK-NEXT: [[MATH]] = extractvalue { i64, i1 } [[TMP0]], 0
; CHECK-NEXT: [[OV:%.*]] = extractvalue { i64, i1 } [[TMP0]], 1
; CHECK-NEXT: [[OV:%.*]] = icmp eq i64 [[IV]], 0
; CHECK-NEXT: br i1 [[OV]], label [[EXIT:%.*]], label [[BACKEDGE]]
; CHECK: backedge:
; CHECK-NEXT: [[SUNKADDR:%.*]] = mul i64 [[MATH]], 4
; CHECK-NEXT: [[SUNKADDR:%.*]] = mul i64 [[IV]], 4
; CHECK-NEXT: [[SUNKADDR1:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[SUNKADDR]]
; CHECK-NEXT: [[LOADED:%.*]] = load atomic i32, ptr [[SUNKADDR1]] unordered, align 4
; CHECK-NEXT: [[SUNKADDR2:%.*]] = getelementptr i8, ptr [[SUNKADDR1]], i64 -4
; CHECK-NEXT: [[LOADED:%.*]] = load atomic i32, ptr [[SUNKADDR2]] unordered, align 4
; CHECK-NEXT: [[MATH]] = add i64 [[IV]], -1
; CHECK-NEXT: [[COND_2:%.*]] = icmp eq i32 [[LOADED]], [[X:%.*]]
; CHECK-NEXT: br i1 [[COND_2]], label [[FAILURE:%.*]], label [[LOOP]]
; CHECK: exit:
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