[PowerPC] Attributes 'zeroext and signext' are incompatible! ptr @omp_get_proc_bind fatal error: error in backend: Broken module found, compilation aborted!

[pkubaj]

FreeBSD 14.0-CURRENT
powerpc64, powerpc64le
llvm-devel 17.0.d20230622_1

Reproducer:

struct CommandCaller {
  CommandCaller();
};
extern "C" {
typedef enum {} omp_proc_bind_t;
omp_proc_bind_t omp_get_proc_bind();
}
CommandCaller::CommandCaller() { omp_get_proc_bind(); }

Compile with:

clang++-devel -cc1 -triple powerpc64le-unknown-freebsd14.0 -emit-obj -O1 -fopenmp CommandCaller-6f8d3a.cpp

Result:

Attributes 'zeroext and signext' are incompatible!
ptr @omp_get_proc_bind
fatal error: error in backend: Broken module found, compilation aborted!

[llvmbot]

@llvm/issue-subscribers-backend-powerpc

[ecnelises]

It looks like happening here:

llvm-project/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp

Lines 376 to 392 in 5b6b2ca

	auto addAttrSet = [&](AttributeSet &FnAS, const AttributeSet &AS,
	bool Param = true) -> void {
	bool HasSignExt = AS.hasAttribute(Attribute::SExt);
	bool HasZeroExt = AS.hasAttribute(Attribute::ZExt);
	if (HasSignExt || HasZeroExt) {
	assert(AS.getNumAttributes() == 1 &&
	"Currently not handling extension attr combined with others.");
	if (Param) {
	if (auto AK = TargetLibraryInfo::getExtAttrForI32Param(T, HasSignExt))
	FnAS = FnAS.addAttribute(Ctx, AK);
	} else
	if (auto AK = TargetLibraryInfo::getExtAttrForI32Return(T, HasSignExt))
	FnAS = FnAS.addAttribute(Ctx, AK);
	} else {
	FnAS = FnAS.addAttributes(Ctx, AS);
	}
	};

Here AS has signext, FnAS has zeroext. The function applies signext to FnAS so that we get declare signext zeroext i32 @omp_get_proc_bind().

[nemanjai]

@ecnelises Do you plan to propose a fix for this?

[ecnelises]

I will try looking into this

[ecnelises]

Return type of omp_get_proc_bind is specified as signext in OMPKinds.def. However the compiler sees enum{} as unsigned because no candidate option is negative. So one workaround is to add a random option equal to -1 in definition of omp_proc_bind_t.

Some other archs (x86_64, aarch64) do not add ext flag to return types. SystemZ has similar behavior to PPC, so -triple s390x also crashes. Maybe return type needs adjustment? FYI @JonPsson