On Tue, May 12, 2015 at 6:36 PM, Fei Ding <fding...@gmail.com> wrote: > I think Thiago and Eric just want to know which code-gen is better and why...
You need to understand for a complex process (CISC ISAs) like x86, there is no one right answer sometimes. You need to look at each micro-arch and understand the pipeline. Sometimes different code stream will performance the same but it also depends on the code size too. Thanks, Andrew Pinski > > 2015-05-12 23:29 GMT+08:00 Eric Botcazou <ebotca...@libertysurf.fr>: >>> Note that at -O3 there is a difference still: >>> clang (3.6.0): >>> addl %esi, %edi >>> movl %edi, %eax >>> retq >>> >>> gcc (4.9.2) >>> leal (%rdi,%rsi), %eax >>> ret >>> >>> Can't tell which is best, if any. >> >> But what's your point exactly here? You cannot expect different compilers to >> generate exactly the same code on a given testcase for non-toy architectures. >> >> Note that this kind of discussion is more appropriate for >> gcc-h...@gcc.gnu.org >> >> -- >> Eric Botcazou
