MemorySanitizer false positive with _mm_cmpneq_sd

[eugenis]

$ cat 1.cc

include <emmintrin.h>

__m128d f(double a, double b) {
__m128d v = _mm_cmpneq_sd(_mm_load_sd(&a), _mm_load_sd(&b));
return v;
}

int main() {
double a = 1.;
double b = 2.;
double * volatile pa = &a;
double * volatile pb = &b;
__m128d c = f(a, b);
return c[0] + c[1];
}

$ ./bin/clang++ ../llvm/1.cc -fsanitize=memory -O1 -g && PATH=bin:$PATH ./a.out
==32151==WARNING: MemorySanitizer: use-of-uninitialized-value
#0 0x4863e7 in f(double, double) /code/build-llvm/../llvm/1.cc:4:15
#1 0x4864bd in main /code/build-llvm/../llvm/1.cc:13:15

[eugenis]

Ah, return c[0] + c[1] is technically incorrect, because the second half of c is garbage.
But MSan crash happens earlier anyway.

[eugenis]

This should be fixed in r267966 + r267967