https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114591
--- Comment #10 from Uroš Bizjak <ubizjak at gmail dot com> --- (In reply to Hongtao Liu from comment #5) > > My experience is memory cost for the operand with rm or separate r, m is > > different which impacts RA decision. > > > > https://gcc.gnu.org/pipermail/gcc-patches/2022-May/595573.html > > Change operands[1] alternative 2 from m -> rm, then RA makes perfect > decision. Yes, I can confirm this oddity: movl v1(%rip), %edx # 5 [c=6 l=6] *zero_extendsidi2/3 movq %rdx, v2(%rip) # 16 [c=4 l=7] *movdi_internal/5 movq %rdx, %rax # 18 [c=4 l=3] *movdi_internal/3 ret # 21 [c=0 l=1] simple_return_internal But even there is room for improvement. The last move can be eliminated by allocating %eax in the first instruction.
