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[BasicAA] Don't use MinAbsVarIndex = 1. #72993

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Nov 21, 2023
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[BasicAA] Don't use MinAbsVarIndex = 1. #72993

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075c0f0
[BasicAA] Don't use MinAbsVarIndex = 1.
fhahn Nov 21, 2023
cc37518
drop fixme
fhahn Nov 21, 2023
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3 changes: 0 additions & 3 deletions llvm/lib/Analysis/BasicAliasAnalysis.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1230,9 +1230,6 @@ AliasResult BasicAAResult::aliasGEP(
const VariableGEPIndex &Var = DecompGEP1.VarIndices[0];
if (Var.Val.TruncBits == 0 &&
isKnownNonZero(Var.Val.V, DL, 0, &AC, Var.CxtI, DT)) {
// If V != 0, then abs(VarIndex) > 0.
MinAbsVarIndex = APInt(Var.Scale.getBitWidth(), 1);

// Check if abs(V*Scale) >= abs(Scale) holds in the presence of
// potentially wrapping math.
auto MultiplyByScaleNoWrap = [](const VariableGEPIndex &Var) {
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5 changes: 2 additions & 3 deletions llvm/test/Analysis/BasicAA/gep-modulo.ll
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Expand Up @@ -326,7 +326,7 @@ define i8 @mul_may_overflow_var_nonzero_minabsvarindex_one_index(ptr %arr, i8 %x
; CHECK-NEXT: PartialAlias (off 917): [2000 x i8]* %arr, i8* %gep.917
; CHECK-NEXT: MayAlias: i8* %gep.917, i8* %gep.idx
; CHECK-NEXT: MustAlias: [2000 x i8]* %arr, i8* %gep.0
; CHECK-NEXT: NoAlias: i8* %gep.0, i8* %gep.idx
; CHECK-NEXT: MayAlias: i8* %gep.0, i8* %gep.idx
; CHECK-NEXT: NoAlias: i8* %gep.0, i8* %gep.917
;
load [2000 x i8], ptr %arr
Expand Down Expand Up @@ -362,10 +362,9 @@ define i8 @mul_nsw_var_nonzero_minabsvarindex_one_index(ptr %arr, i8 %x, i64 %v)
ret i8 %l
}

; FIXME: %gep and %p can alias.
define i8 @test_pr72831_may_wrap(i64 %off) {
; CHECK-LABEL: Function: test_pr72831_may_wrap: 2 pointers, 0 call sites
; CHECK-NEXT: NoAlias: i8* %gep, i8* %p
; CHECK-NEXT: MayAlias: i8* %gep, i8* %p
entry:
%p = alloca [2 x i8], align 1
%ext = zext i1 false to i64
Expand Down