http://llvm.org/bugs/show_bug.cgi?id=22024
Quentin Colombet <[email protected]> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED CC| |[email protected] Resolution|--- |WONTFIX --- Comment #4 from Quentin Colombet <[email protected]> --- As far as I know, xorps A,A,A are good for performance because it tells that A is zeroed. In this particular case, it even helps to break a scheduling dependency. Indeed, the out of order engine would see two independent computation: vcvtsi2ssq %rcx, %xmm0, %xmm0 vmovss %xmm0, (%rsi) and vcvtsi2ssq %rdx, %xmm0, %xmm0 vmovss %xmm0, (%rdi) Instead of one big computation: vcvtsi2ssq %rcx, %xmm0, %xmm0 vmovss %xmm0, (%rsi) vcvtsi2ssq %rdx, %xmm0, %xmm0 # <-- we do not know that the xmm0 given as input is independent of the previous convert. vmovss %xmm0, (%rdi) If you actually see a performance problem, feel free to reopen. Thanks. -- You are receiving this mail because: You are on the CC list for the bug.
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