Re: [PATCH] On x86 allow if-conversion of more than one insn as long as there is at most one cmov (PR tree-optimization/79390)

[Segher Boessenkool <segher@kernel.crashing.org>]

Hi,

On Sat, Apr 01, 2017 at 02:20:27PM +0200, Jakub Jelinek wrote:
> As discussed in the PR, in the following testcase we don't if-convert
> with the generic (and many other) tuning, because we default to
> --param max-rtl-if-conversion-insns=1 in most of the tunings.
> The problem we have is with multiple cmov instructions, but in the
> testcase there is just one cmov and the other insn is turned into a SSE
> max insn, which is fine.
> 
> This patch stops artificially lowering that param, and for one_if_conv_insn
> tuning it instead rejects the if-conversion if the resulting sequence has
> multiple cmov instructions.  The hook is passed if_info too, so it can
> in the future do better heuristics based on predictability of the edges,
> how far the uses of the cmov result are (I assume cmov major problem is
> latency, right?) etc.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Does this change anything for targets that do not implement the new hook?
It isn't immediately obvious from the patch.


Segher