GCC won`t emit my instriction
Mon Jun 10 22:20:00 GMT 2019
On Sun, Jun 9, 2019 at 11:15 PM Alex Hill via gcc-help
> I found some decision, i used flags -fexceptions -fnon-call-exceptions and it emits max insn, now i try to understand why this happens.
> Here is the max it emits:
> (define_insn "smax<GPR:mode>3"
> [(set (match_operand:GPR 0 "register_operand" "=r")
> (smax:GPR (match_operand:GPR 1 "register_operand" " r")
> (match_operand:GPR 2 "register_operand" " r")))]
> [(set_attr "type" "move")
> (set_attr "mode" "<MODE>")])
There is some code in noce_try_minmax in ifcvt.c that will try to
recognize an if statement in RTL that performs min/max and try to
convert it to a direct min/max operation. However, in general, you
are more likely to get a min/max operation if you recognize it when
parsing, and then carry it all of the way through the optimizer. To
make that work, you need min/max named patterns, that emit min/max
operations in RTL. Like what you have immediately above. If trying
to understand how this works, look at the debugging dumps you can get
with -fdump-tree-all and -fdump-rtl-all when compiling a trivial
testcase. And maybe compare with another CPU target that already has
working min/max support.
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