Michael Schwendt wrote: > On Wed, 23 Oct 2002 17:36:14 -0400, Jakub Jelinek wrote: >>>A test using a simple C source file: >>>-march=i386 -mcpu=i686 was the same as -march=i386 -mcpu=athlon >>>Most interesting to me, >>>The mix is different. >>> >>>example >>>i686 athlon >>>movl -24(%edp), %edx andl -24(%edp), %eax >>>andl %edx, %eax >>> >>> >>>movl %eax, %edx imull $100, %eax, %edx >>>movl %edx, %eax >>>sall $2, %eax >>>addl %edx, %eax >>>leal 0(,%eax,4), %edx >>>addl %edx, %eax >>>leal 0(,%eax,4), %edx >> >>Do you have testcase and exact options for this? >>$edx = 100*$eax is with -O2 -mcpu=i686: >> leal (%eax,%eax,4), %edx >> leal (%edx,%edx,4), %edx >> sall $2, %edx >>for me. > > > I think Thomas didn't use -O2. Correct. I was comparing the code/scheduler differences in -mcpu settings. adding -O2 for the previous example: i686 athlon movl -24(%ebp), %ebx movl -24(%ebp), %ecx movl -28(%ebp), %edx movl %ecx, %eax movl %ebx, %eax subl -28(%ebp), %eax subl %edx, %eax imull $100, %eax, %edx leal (%eax,%eax,4), %eax movl %edx, %eax leal (%eax,%eax,4), %eax leal 0(,%eax,4), %edx movl %edx, %eax Some other code is mixed in now, but still i686 is using leal and athlon is using imull. So gcc thinks imul is a better choice on the athlon than i686. also this one I like: i686 athlon xorl %edi, %edi testb $32, 9(%edx) xorl %esi, %esi movl $0, -9836(%ebp) testb $32, 9(%ecx) movl $0, -9840(%ebp) movl %edi, -9836(%ebp) movl %esi, -9840(%ebp) I see slightly different register usage again, but the interesting part is i686 using xorl, and 2 registers, while the athlon uses constants. Still I need something to test with to see how much difference it makes when running. -Thomas -- Psyche-list mailing list Psyche-list@redhat.com https://listman.redhat.com/mailman/listinfo/psyche-list
