https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102840
--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> --- (In reply to Roger Sayle from comment #1) > I believe this test case is poorly written, and not correctly testing the > original issue in PR target/22076 which concerned suboptimal moving of > arguments via memory (fixed by prohibiting reload using mmx registers). > > Prior to my patch, with -m32 -O2 -fomit-frame-pointer -mmmx -mno-sse2, GCC > generated: > > test: movq .LC1, %mm0 > paddb .LC0, %mm0 > movq %mm0, x > ret > > .x: .zero 8 > .LC0: .byte 1 > .byte 2 > .byte 3 > .byte 4 > .byte 5 > .byte 6 > .byte 7 > .byte 8 > .LC1: .byte 11 > .byte 22 > .byte 33 > .byte 44 > .byte 55 > .byte 66 > .byte 77 > .byte 88 > > which indeed doesn't use movl, and requires two movq. > > After my patch, we now generate the much more efficient (dare I say optimal): > test: movl $807671820, %eax > movl $1616136252, %edx > movl %eax, x > movl %edx, x+4 > ret > > which has evaluated the _mm_add_pi8 at compile-time, and effectively memsets > x to the correct value in the minimum possible number of cycles. In fact, > failing to evaluate this at compile-time is a regression since v4.1 > (according to godbolt) If your analysis is correct, why does -m64 stay the same?
