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[AIX][AsmPrinter] Fix unsigned subtraction wrap-around (#122214)

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Unsigned subtraction wrap-around occurs in `emitGlobalConstantImpl` on
an AIX-specific code path from 8e4423eb0888 when a structure type has
zero elements.

With assertions enabled, this manifests as:
```
TypeSize llvm::StructLayout::getElementOffset(unsigned int) const: Assertion `Idx < NumElements && "Invalid element idx!"' failed.
```
This commit is contained in:
Hubert Tong 2025-01-09 00:07:57 -04:00 committed by GitHub
parent c6b7bd42d5
commit e438513f2e
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
2 changed files with 34 additions and 13 deletions
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27
llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
View File

@ -3914,21 +3914,22 @@ static void emitGlobalConstantImpl(const DataLayout &DL, const Constant *CV,
if (isa<ConstantAggregateZero>(CV)) {
StructType *structType;
if (AliasList && (structType = llvm::dyn_cast<StructType>(CV->getType()))) {
// Handle cases of aliases to direct struct elements
const StructLayout *Layout = DL.getStructLayout(structType);
uint64_t SizeSoFar = 0;
for (unsigned int i = 0, n = structType->getNumElements(); i < n - 1;
++i) {
uint64_t GapToNext = Layout->getElementOffset(i + 1) - SizeSoFar;
AP.OutStreamer->emitZeros(GapToNext);
SizeSoFar += GapToNext;
emitGlobalAliasInline(AP, Offset + SizeSoFar, AliasList);
unsigned numElements = {structType->getNumElements()};
if (numElements != 0) {
// Handle cases of aliases to direct struct elements
const StructLayout *Layout = DL.getStructLayout(structType);
uint64_t SizeSoFar = 0;
for (unsigned int i = 0; i < numElements - 1; ++i) {
uint64_t GapToNext = Layout->getElementOffset(i + 1) - SizeSoFar;
AP.OutStreamer->emitZeros(GapToNext);
SizeSoFar += GapToNext;
emitGlobalAliasInline(AP, Offset + SizeSoFar, AliasList);
}
AP.OutStreamer->emitZeros(Size - SizeSoFar);
return;
}
AP.OutStreamer->emitZeros(Size - SizeSoFar);
return;
} else {
return AP.OutStreamer->emitZeros(Size);
}
return AP.OutStreamer->emitZeros(Size);
}
if (isa<UndefValue>(CV))

20
llvm/test/CodeGen/PowerPC/global-merge-aix-zero-size-struct.ll Normal file
View File

@ -0,0 +1,20 @@
; RUN: llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff -mcpu=pwr7 < %s | FileCheck %s
; RUN: llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff -mcpu=pwr7 --filetype=obj -o %t.o < %s
; RUN: llvm-objdump --syms %t.o | FileCheck %s --check-prefix=OBJ
%struct.anon = type {}
@a = internal constant %struct.anon zeroinitializer, align 1
@b = internal constant [6 x i8] c"hello\00", align 1
; CHECK: .csect L.._MergedGlobals[RO],2
; CHECK-NEXT: .lglobl a # @_MergedGlobals
; CHECK-NEXT: .lglobl b
; CHECK-NEXT: a:
; CHECK-NEXT: b:
; CHECK-NEXT: .string "hello"
; OBJ: 0000000000000000 l .text 0000000000000006 L.._MergedGlobals
; OBJ-NEXT: 0000000000000000 l .text (csect: L.._MergedGlobals) 0000000000000000 a
; OBJ-NEXT: 0000000000000000 l .text (csect: L.._MergedGlobals) 0000000000000000 b