[LLVMdev] [CLang] Comparing vector types - invalid error and proposed fix
Martin O'Riordan
Martin.ORiordan at movidius.com
Wed Oct 2 06:25:31 PDT 2013
I was investigating an error diagnostic in the following test example:
typedef signed char char16 __attribute__((ext_vector_type(16)));
void test( char16 srcA, char16 srcB, char16 *dst) {
*dst = ( srcA == srcB );
}
which produces the message:
mismatch.c:5:10: error: assigning to 'char16' from incompatible type
'char __attribute__((ext_vector_type(16)))'
*dst = ( srcA == srcB );
^ ~~~~~~~~~~~~~~~~
1 error generated.
There appear to be two things going on here. The first is the notion of
compatible types which are not supported by GCC/CLang for vector extensions,
even in the trivial case where 'signed char' == 'char' (in C).
The second thing is that the result of a comparison between two vectors is
supposed to result in the a 'signed' integer vector result.
'char' is always troublesome, though in C++ it is a discrete type. I made
the following change in my copy (clang-3.3) that I think is a correct and
valid change:
File: tools/clang/lib/Sema/SemaChecking.cpp
Function: Sema::GetSignedVectorType()
Replace the fragment:
if (TypeSize == Context.getTypeSize(Context.CharTy))
return Context.getExtVectorType(Context.CharTy,
VTy->getNumElements());
^^^^^^
with:
if (TypeSize == Context.getTypeSize(Context.CharTy))
return Context.getExtVectorType(Context.SignedCharTy,
VTy->getNumElements());
^^^^^^^^^^^^
I would like to propose this as a fix for a future release of CLang.
Thanks,
Martin O'Riordan - Movidius Ltd.
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