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[Clang][CodeGen] Respect -fwrapv-pointer when emitting struct GEPs #134269

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Merged
merged 1 commit into from
Apr 9, 2025
Merged

[Clang][CodeGen] Respect -fwrapv-pointer when emitting struct GEPs #134269

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11 changes: 9 additions & 2 deletions clang/lib/CodeGen/CGExpr.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4922,6 +4922,9 @@ static Address emitAddrOfFieldStorage(CodeGenFunction &CGF, Address base,
unsigned idx =
CGF.CGM.getTypes().getCGRecordLayout(rec).getLLVMFieldNo(field);

if (CGF.getLangOpts().PointerOverflowDefined)
return CGF.Builder.CreateConstGEP2_32(base, 0, idx, field->getName());

return CGF.Builder.CreateStructGEP(base, idx, field->getName());
}

Expand Down Expand Up @@ -4979,9 +4982,13 @@ LValue CodeGenFunction::EmitLValueForField(LValue base,
if (!UseVolatile) {
if (!IsInPreservedAIRegion &&
(!getDebugInfo() || !rec->hasAttr<BPFPreserveAccessIndexAttr>())) {
if (Idx != 0)
if (Idx != 0) {
// For structs, we GEP to the field that the record layout suggests.
Addr = Builder.CreateStructGEP(Addr, Idx, field->getName());
if (getLangOpts().PointerOverflowDefined)
Addr = Builder.CreateConstGEP2_32(Addr, 0, Idx, field->getName());
else
Addr = Builder.CreateStructGEP(Addr, Idx, field->getName());
}
} else {
llvm::DIType *DbgInfo = getDebugInfo()->getOrCreateRecordType(
getContext().getRecordType(rec), rec->getLocation());
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21 changes: 21 additions & 0 deletions clang/test/CodeGen/pointer-overflow.c
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Expand Up @@ -10,3 +10,24 @@ void test(void) {
// DEFAULT: getelementptr inbounds nuw i32, ptr
// FWRAPV-POINTER: getelementptr i32, ptr
}

struct S {
int a;
int b;
int c: 10;
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@shafik shafik Apr 8, 2025

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I am curious why did you add bit-fields in specifically to this test? Are they particularly different wrt other types of fields like arrays, pointers, member pointers etc that we would expect them to break?

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@dtcxzyw dtcxzyw Apr 8, 2025

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Bitfields are handled by a different code path:

llvm-project/clang/lib/CodeGen/CGExpr.cpp

Line 4977 in 2c1bdd4

Addr = Builder.CreateStructGEP(Addr, Idx, field->getName());

int d: 10;
};

int test_struct(struct S* s) {
// -fwrapv-pointer should turn off inbounds nuw for struct GEP's
return s->b;
// DEFAULT: getelementptr inbounds nuw %struct.S, ptr
// FWRAPV-POINTER: getelementptr %struct.S, ptr
}

int test_struct_bitfield(struct S* s) {
// -fwrapv-pointer should turn off inbounds nuw for struct GEP's
return s->d;
// DEFAULT: getelementptr inbounds nuw %struct.S, ptr
// FWRAPV-POINTER: getelementptr %struct.S, ptr
}