https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80124
Bug ID: 80124
Summary: Possible bug in _mm_cmpeq_ps
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: guille at berkeley dot edu
Target Milestone: ---
The following code (below) seems to trigger a gcc bug because the following:
(A) * _mm_cmpeq_ps(r, r)
(B) * _mm_castsi128_ps(_mm_cmpeq_epi32(_mm_castps_si128(r),
_mm_castps_si128(r)))
which should give the same result, don't.
In particular (B) seems to give the correct result, but (A) doesn't.
* I tested it on:
"gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-apple-darwin16.4.0/7.0.1/lto-wrapper
Target: x86_64-apple-darwin16.4.0
Configured with: ../configure --without-multilib --enable-languages=c,c++
Thread model: posix
gcc version 7.0.1 20170129 (experimental) (GCC)"
* no flags are necessary (other than maybe '-msse -msse2')
--------------------------------------------------------------------------------
#include <iostream>
#include <cassert>
#include <xmmintrin.h>
#include <emmintrin.h>
#if !defined(__SSE__) || !defined(__SSE2__)
#error "needs SSE+SSE2"
#else
static void helper_print(const char name[], const __m128 v)
{
for (int i = 0; i < 4; ++i)
{
std::cerr << name << "[" << i << "] = ";
for (int j = 31; j >= 0; --j) std::cerr << ((((const unsigned int
*)&v)[i] >> j) & 1);
std::cerr << ";\n";
}
}
static __m128 ones()
{
const __m128 u = _mm_undefined_ps();
const __m128 r = _mm_cmpeq_ps(u, u);
if (_mm_movemask_ps(_mm_cmpeq_ps(r, r)) != 0xf) //
in case of error, print debugging info
{
helper_print("r", r);
const __m128 cmp = _mm_cmpeq_ps(r, r);
helper_print("cmp", cmp); //
<-- this should be all 1s, but is all 0s
std::cerr << "_mm_movemask_ps(cmp)=" << _mm_movemask_ps(cmp) << "\n";
}
//
assert(_mm_movemask_ps(_mm_castsi128_ps(_mm_cmpeq_epi32(_mm_castps_si128(r),
_mm_castps_si128(r)))) == 0xf); // <-- this passes
assert(_mm_movemask_ps(_mm_cmpeq_ps(r, r)) == 0xf);
// <-- this breaks!
return r;
}
#endif
int main()
{
[[maybe_unused]] const __m128 r = ones();
return 0;
}
