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Re: [committed] [PR tree-optimization/86010] More aggressively trim partially dead mem* and str* calls
- From: Christophe Lyon <christophe dot lyon at linaro dot org>
- To: Jeff Law <law at redhat dot com>
- Cc: gcc Patches <gcc-patches at gcc dot gnu dot org>
- Date: Fri, 6 Jul 2018 14:08:38 +0200
- Subject: Re: [committed] [PR tree-optimization/86010] More aggressively trim partially dead mem* and str* calls
- References: <86e95146-d9de-f898-84b0-6ca3a8da76af@redhat.com>
Hi Jeff,
On Fri, 6 Jul 2018 at 05:44, Jeff Law <law@redhat.com> wrote:
>
> As noted in BZ 86010 we can be more aggressive when trimming tails of
> mem* or str* calls in gimple DSE since trimming a tail doesn't affect
> alignment and residuals are usually handled pretty efficiently in libc.
>
> Additionally, if the total number of live bytes left is smaller than a
> word, then it's highly likely we'll open-code the mem* or str* routine.
> So we allow more aggressive trimming in that case too.
>
> What's left to be able to close out 86010 is to identify when a memory
> store could be merged with a subsequent memset. I'm skeptical of the
> importance of that optimization, though perhaps it comes up often enough
> with structure initializations to be worth doing.
>
> Bootstrapped and regression tested on x86_64-linux-gnu. Installing on
> the trunk.
>
This is causing a regression on arm and i686:
gcc.dg/tree-ssa/pr30375.c: pattern found 0 times
FAIL: gcc.dg/tree-ssa/pr30375.c scan-tree-dump-times dse1
"MEM\\[\\(struct _s \\*\\)&signInfo \\+ [0-9]+B\\] = {}" 1
> Jeff