https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94300
Bug ID: 94300 Summary: [10 Regression] memcpy vector load miscompiled during const-prop Product: gcc Version: 10.0 Status: UNCONFIRMED Keywords: wrong-code Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: kretz at kde dot org Target Milestone: --- Target: x86_64-*-*, i?86-*-* Test case `-O1 -march=skylake-avx512`: int main() { double mem[16]; using V [[gnu::vector_size(64)]] = double; const V a{0, 1, 2, 3, 4, 5, 6, 7}; const V b{8, 9, 10, 11, 12, 13, 14, 15}; __builtin_memcpy(mem, &a, 64); __builtin_memcpy(mem + 8, &b, 64); V c = {}; __builtin_memcpy(&c, mem + 4, 64); if (c[5] != double(9)) __builtin_abort(); } >From my extended test case, where c would be {4, 5, 6, 7, 8, 15, 9, 10}. If GCC is made to forget the contents of mem (e.g. inline-asm), the test does not fail. GCC9 does not do constant evaluation of the code above and therefore doesn't fail.