https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47582
--- Comment #2 from Tony Poppleton <tony.poppleton at gmail dot com> ---
Re-testing this with GCC 5.1, the code appears to be even less efficient, for
both cases;
DM1:
.LFB0:
.cfi_startproc
movss b(%rip), %xmm0
xorl %eax, %eax
movss %xmm0, a(%rip)
movss b+4(%rip), %xmm0
movss %xmm0, a+4(%rip)
movss b+8(%rip), %xmm0
movss %xmm0, a+8(%rip)
movss b+12(%rip), %xmm0
movss %xmm0, a+12(%rip)
movss b+16(%rip), %xmm0
movss %xmm0, a+16(%rip)
ret
.cfi_endproc
.LFB0:
.cfi_startproc
movq b(%rip), %rax
movq %rax, a(%rip)
movq b+8(%rip), %rax
movq %rax, a+8(%rip)
movl b+16(%rip), %eax
movl %eax, a+16(%rip)
xorl %eax, %eax
ret
.cfi_endproc
Why is the "xorl" appearing in both cases? Should this be logged as a separate
bug.
Incidentally, compiling with -O1 produces the same code as -O2 on older GCCs
(as in the description comment above)
My total guess is it is due to a and b not having any initial values, and an
optimization that takes into account value ranges is getting confused?
