https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97832
--- Comment #16 from Michael_S <already5chosen at yahoo dot com> --- On unrelated note, why loop overhead uses so many instructions? Assuming that I am as misguided as gcc about load-op combining, I would write it as: sub %rax, %rdx .L3: vmovupd (%rdx,%rax), %ymm1 vmovupd 32(%rdx,%rax), %ymm0 vfmadd213pd 32(%rax), %ymm3, %ymm1 vfnmadd213pd (%rax), %ymm2, %ymm0 vfnmadd231pd 32(%rdx,%rax), %ymm3, %ymm0 vfnmadd231pd (%rdx,%rax), %ymm2, %ymm1 vmovupd %ymm0, (%rax) vmovupd %ymm1, 32(%rax) addq $64, %rax decl %esi jb .L3 The loop overhead in my variant is 3 x86 instructions==2 macro-ops, vs 5 x86 instructions==4 macro-ops in gcc variant. Also, in gcc variant all memory accesses have displacement that makes them 1 byte longer. In my variant only half of accesses have displacement. I think, in the past I had seen cases where gcc generates optimal or near-optimal code sequences for loop overhead. I wonder why it can not do it here.
