https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85482
Bug ID: 85482
Summary: unnecessary vmovaps/vmovapd/vmovdqa emitted
Product: gcc
Version: 8.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: kretz at kde dot org
Target Milestone: ---
Test case (cf. https://godbolt.org/g/QkJYSK):
#include <x86intrin.h>
__m256 zero_extend1(__m128 a) {
return _mm256_insertf128_ps(__m256(), a, 0);
}
__m256d zero_extend1(__m128d a) {
return _mm256_insertf128_pd(__m256d(), a, 0);
}
__m256i zero_extend1(__m128i a) {
return _mm256_insertf128_si256(__m256i(), a, 0);
}
__m512 zero_extend2(__m128 a) {
return _mm512_insertf32x4(__m512(), a, 0);
}
__m512d zero_extend2(__m128d a) {
return _mm512_insertf64x2(__m512d(), a, 0);
}
__m512i zero_extend2(__m128i a) {
return _mm512_inserti32x4(__m512i(), a, 0);
}
__m512 zero_extend3(__m256 a) {
return _mm512_insertf32x8(__m512(), a, 0);
}
__m512d zero_extend3(__m256d a) {
return _mm512_insertf64x4(__m512d(), a, 0);
}
__m512i zero_extend3(__m256i a) {
return _mm512_inserti64x4(__m512i(), a, 0);
}
template <class T> T blackhole;
void test(void *mem) {
blackhole<__m256 > = zero_extend1(_mm_load_ps((float *)mem));
blackhole<__m256d> = zero_extend1(_mm_load_pd((double *)mem));
blackhole<__m256i> = zero_extend1(_mm_load_si128((__m128i *)mem));
blackhole<__m512 > = zero_extend2(_mm_load_ps((float *)mem));
blackhole<__m512d> = zero_extend2(_mm_load_pd((double *)mem));
blackhole<__m512i> = zero_extend2(_mm_load_si128((__m128i *)mem));
blackhole<__m512 > = zero_extend3(_mm256_load_ps((float *)mem));
blackhole<__m512d> = zero_extend3(_mm256_load_pd((double *)mem));
blackhole<__m512i> = zero_extend3(_mm256_load_si256((__m256i *)mem));
}
Between every load and store instruction in the `test` function, the
vmov(aps|apd|dqa) is superfluous. The preceding load instruction already zeroes
the high bits. Instead of the load instruction, there could also be a different
instructions, or instruction sequences, that already guarantee the high bits to
be zero.
