[OpenMP] Strict aliasing violation in TargetValue::getValue()

[nikic]

This bit of code looks a bit suspect:

llvm-project/openmp/libompd/src/TargetValue.h

Lines 232 to 252 in 24a39f3

	template <typename T> ompd_rc_t TBaseValue::getValue(T &buf) {
	assert(sizeof(T) >= baseTypeSize);
	ompd_rc_t ret = getValue(&buf, 1);
	if (sizeof(T) > baseTypeSize) {
	switch (baseTypeSize) {
	case 1:
	buf = (T) * ((int8_t *)&buf);
	break;
	case 2:
	buf = (T) * ((int16_t *)&buf);
	break;
	case 4:
	buf = (T) * ((int32_t *)&buf);
	break;
	case 8:
	buf = (T) * ((int64_t *)&buf);
	break;
	}
	}
	return ret;
	}

This passes in T& buf, then reads into it via getValue() -- this part is fine, as that's essentially done via memcpy.

But then buf is cast to uintN_t *, dereferenced, cast to T and written back to buf. This is not compatible with strict aliasing in C.

[llvmbot]

@llvm/issue-subscribers-openmp

Author: Nikita Popov (nikic)

This bit of code looks a bit suspect: https://github.com/llvm/llvm-project/blob/24a39f364dbef7e18d36be3919eacde32125df5e/openmp/libompd/src/TargetValue.h#L232-L252

This passes in T& buf, then reads into it via getValue() -- this part is fine, as that's essentially done via memcpy.

But then buf is cast to uintN_t *, dereferenced, cast to T and written back to buf. This is not compatible with strict aliasing in C.