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[ValueTracking] Fix Overflow with i1 Constant GEPs #125470

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[ValueTracking] Fix Overflow with i1 Constant GEPs #125470

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7 changes: 5 additions & 2 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1477,8 +1477,11 @@ static void computeKnownBitsFromOperator(const Operator *I,
// that this is a multiple of the minimum size.
ScalingFactor.Zero.setLowBits(llvm::countr_zero(TypeSizeInBytes));
} else if (IndexBits.isConstant()) {
APInt IndexConst = IndexBits.getConstant();
APInt ScalingFactor(IndexBitWidth, TypeSizeInBytes);
// i1 is a valid GEP index, ensure we have enough space to do the
// computation in that case.
unsigned CalcBitWidth = std::max(IndexBitWidth, 8u);
APInt IndexConst = IndexBits.getConstant().zext(CalcBitWidth);
APInt ScalingFactor(CalcBitWidth, TypeSizeInBytes);
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We should be setting IndexBitWidth above to the index type size from DataLayout, and then sextOrTrunc from the size of the index. What the code currently does is just incorrect.

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and then sextOrTrunc from the size of the index

Which value should be sextOrTrunc'd ? Do you mean IndexConst.sextOrTrunc below should use the GEP Operand type width, and all the rest use the DL Index type size?

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The correct logic here is quite tricky. Do you mind if I fix this myself?

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Here it is: #125532

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@nikic Thank you, your patch fixes the testcase so it's good on my end! 😄

IndexConst *= ScalingFactor;
AccConstIndices += IndexConst.sextOrTrunc(BitWidth);
continue;
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19 changes: 19 additions & 0 deletions llvm/test/Transforms/LoadStoreVectorizer/AMDGPU/knownbits-gep-i1.ll
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@@ -0,0 +1,19 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt -mtriple=amdgcn-amd-amdhsa -mcpu=gfx942 -passes=load-store-vectorizer -S -o - %s | FileCheck %s

define amdgpu_kernel void @simple_users_scores() {
; CHECK-LABEL: define amdgpu_kernel void @simple_users_scores(
; CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[SIMPLEUSER:%.*]] = alloca [4 x i64], i32 0, align 4, addrspace(5)
; CHECK-NEXT: [[G:%.*]] = getelementptr i32, ptr addrspace(5) [[SIMPLEUSER]], i1 true
; CHECK-NEXT: store <2 x i32> zeroinitializer, ptr addrspace(5) [[G]], align 4
; CHECK-NEXT: ret void
;
entry:
%simpleuser = alloca [4 x i64], i32 0, align 4, addrspace(5)
store i32 0, ptr addrspace(5) %simpleuser, align 4
%G = getelementptr i32, ptr addrspace(5) %simpleuser, i1 true
store i32 0, ptr addrspace(5) %G, align 4
ret void
}