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[SimplifyCFG] Bail out on vector GEPs in passingValueIsAlwaysUndefined #142526

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Merged
merged 2 commits into from
Jun 4, 2025
Merged

[SimplifyCFG] Bail out on vector GEPs in passingValueIsAlwaysUndefined #142526

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a9f51cb
[SimplifyCFG] Handle vector GEP in `passingValueIsAlwaysUndefined`
dtcxzyw Jun 3, 2025
37b60e4
[InstCombine] Address review comments.
dtcxzyw Jun 3, 2025
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5 changes: 5 additions & 0 deletions llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8109,6 +8109,7 @@ bool SimplifyCFGOpt::simplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {

/// Check if passing a value to an instruction will cause undefined behavior.
static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValueMayBeModified) {
assert(V->getType() == I->getType() && "Mismatched types");
Constant *C = dyn_cast<Constant>(V);
if (!C)
return false;
Expand Down Expand Up @@ -8166,6 +8167,10 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
// Look through GEPs. A load from a GEP derived from NULL is still undefined
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User))
if (GEP->getPointerOperand() == I) {
// The type of GEP may differ from the type of base pointer.
// Bail out on vector GEPs, as they are not handled by other checks.
if (GEP->getType()->isVectorTy())
return false;
// The current base address is null, there are four cases to consider:
// getelementptr (TY, null, 0) -> null
// getelementptr (TY, null, not zero) -> may be modified
Expand Down
20 changes: 20 additions & 0 deletions llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll
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Expand Up @@ -244,6 +244,7 @@ declare ptr @fn_nonnull_arg(ptr nonnull %p)
declare ptr @fn_noundef_arg(ptr noundef %p)
declare ptr @fn_ptr_arg(ptr)
declare ptr @fn_ptr_arg_nounwind_willreturn(ptr) nounwind willreturn
declare void @fn_arg_vec(<2 x ptr>)

define void @test9(i1 %X, ptr %Y) {
; CHECK-LABEL: @test9(
Expand Down Expand Up @@ -917,6 +918,25 @@ bb5: ; preds = %bb3, %bb
ret i32 %i7
}

define void @test9_gep_splat(i1 %X, ptr %Y) {
; CHECK-LABEL: @test9_gep_splat(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[SPEC_SELECT:%.*]] = select i1 [[X:%.*]], ptr null, ptr [[Y:%.*]]
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i8, ptr [[SPEC_SELECT]], <2 x i64> zeroinitializer
; CHECK-NEXT: call void @fn_arg_vec(<2 x ptr> [[GEP]])
; CHECK-NEXT: ret void
;
entry:
br i1 %X, label %if, label %else
if:
br label %else
else:
%phi = phi ptr [ %Y, %entry ], [ null, %if ]
%gep = getelementptr i8, ptr %phi, <2 x i64> zeroinitializer
call void @fn_arg_vec(<2 x ptr> %gep)
ret void
}

declare void @side.effect()
declare i8 @get.i8()

Expand Down