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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)
- From: Segher Boessenkool <segher at kernel dot crashing dot org>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Uros Bizjak <ubizjak at gmail dot com>, Jeff Law <law at redhat dot com>, Bernd Schmidt <bschmidt at redhat dot com>, gcc-patches at gcc dot gnu dot org
- Date: Sat, 1 Apr 2017 13:43:36 -0500
- Subject: 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)
- Authentication-results: sourceware.org; auth=none
- References: <20170401122027.GT17461@tucnak>
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