https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40135
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> --- For reference I see for example FAIL: gcc.target/i386/avx2-vpblendd128-2.c execution test FAIL: gcc.target/i386/avx2-vpblendd256-2.c execution test FAIL: gcc.target/i386/avx2-vpblendw-2.c execution test FAIL: gcc.target/i386/avx2-vpbroadcastd128-2.c execution test FAIL: gcc.target/i386/avx2-vpbroadcastd256-2.c execution test FAIL: gcc.target/i386/avx2-vpbroadcastw128-2.c execution test FAIL: gcc.target/i386/avx2-vpbroadcastw256-2.c execution test FAIL: gcc.target/i386/avx2-vpermd-2.c execution test FAIL: gcc.target/i386/avx2-vpermps-2.c execution test FAIL: gcc.target/i386/avx2-vpmaxsd-2.c execution test FAIL: gcc.target/i386/avx2-vpmaxsw-2.c execution test FAIL: gcc.target/i386/avx2-vpmaxud-2.c execution test FAIL: gcc.target/i386/avx2-vpmaxuw-2.c execution test FAIL: gcc.target/i386/avx2-vpminsd-2.c execution test FAIL: gcc.target/i386/avx2-vpminsw-2.c execution test FAIL: gcc.target/i386/avx2-vpminud-2.c execution test FAIL: gcc.target/i386/avx2-vpminuw-2.c execution test FAIL: gcc.target/i386/avx2-vpmuldq-2.c execution test FAIL: gcc.target/i386/avx2-vpmulhrsw-2.c execution test FAIL: gcc.target/i386/avx2-vpmulhuw-2.c execution test FAIL: gcc.target/i386/avx2-vpmulhw-2.c execution test FAIL: gcc.target/i386/avx2-vpmulld-2.c execution test ... FAIL: gcc.target/i386/avx2-vpunpckhdq-2.c execution test FAIL: gcc.target/i386/avx2-vpunpckhwd-2.c execution test FAIL: gcc.target/i386/avx2-vpunpckldq-2.c execution test FAIL: gcc.target/i386/avx2-vpunpcklwd-2.c execution test but for example gcc.target/i386/avx2-vpblendd128-2.c contains "invalid" type-punning through unions: static void init_pblendd128 (int *src1, int *src2, int seed) { int i, sign = 1; for (i = 0; i < 4; i++) { src1[i] = (i + seed) * (i + seed) * sign; src2[i] = (i + seed + 20) * sign; sign = -sign; } } ... static void avx2_test (void) { union128i_d src1, src2, dst; int dst_ref[4]; int i; for (i = 0; i < NUM; i++) { init_pblendd128 (src1.a, src2.a, i); dst.x = _mm_blend_epi32 (src1.x, src2.x, MASK); which stores into src1/src2 via a pointer access and only reads via a direct access to the union. That's not how the GCC extension specifies union type-punning. I've filed PR63211 for that. Here the stores do not end up in alias-set zero and with removing the c-common.c hack the loads also end up not using alias-set zero. Without the fix the loads use alias-set zero and thus keep the int-stores live. There is also no easy must-alias to identify here as the stores happen in a loop.