https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89774
JunMa <JunMa at linux dot alibaba.com> changed:
What |Removed |Added
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CC| |JunMa at linux dot alibaba.com
--- Comment #10 from JunMa <JunMa at linux dot alibaba.com> ---
(In reply to Segher Boessenkool from comment #9)
> We currently only do it for trivial cases, as the example in comment 6 shows
> as well. This is done during expand, which is the wrong place for it.
>
> PR90070 is asking for better optimisation of this: do the operation in single
> precision, and use single-precision constants, if this does not change the
> result (or there is some -ffast-math option).
>
> PR22326 is also closely related. I don't think we can close any of these PRs
> as a dup of another, they are all asking for slightly different things :-)
clang can do this optimization in instcombine pass. see this case:
float f4( float x ) {double t = x + 2.0; return t; }
float f5( float x ) {return x + 2.0; }
compiled with -O2 -march=native, GCC gives:
f4:
vcvtss2sd %xmm0, %xmm0, %xmm0
vaddsd .LC1(%rip), %xmm0, %xmm0
vcvtsd2ss %xmm0, %xmm0, %xmm0
ret
f5:
vaddss .LC3(%rip), %xmm0, %xmm0
ret
while clang always emits vaddss instruction.
