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Re: Builtin expansion versus headers optimization: Reductions

From: Jeff Law <law at redhat dot com>
To: Jakub Jelinek <jakub at redhat dot com>, Joseph Myers <joseph at codesourcery dot com>
Cc: OndÅej BÃlka <neleai at seznam dot cz>, gcc at gcc dot gnu dot org, law at redhat dot org, libc-alpha at sourceware dot org
Date: Thu, 04 Jun 2015 07:15:15 -0600
Subject: Re: Builtin expansion versus headers optimization: Reductions
Authentication-results: sourceware.org; auth=none
References: <20150604105929 dot GA19141 at domone> <alpine dot DEB dot 2 dot 10 dot 1506041206200 dot 31862 at digraph dot polyomino dot org dot uk> <20150604123319 dot GF10247 at tucnak dot redhat dot com>

On 06/04/2015 06:33 AM, Jakub Jelinek wrote:

On Thu, Jun 04, 2015 at 12:26:03PM +0000, Joseph Myers wrote:

Again is this worth a gcc pass?


This isn't a matter of compiler passes; it's additional checks in existing
built-in function handling.  Maybe that built-in function handling should
move to the match-and-simplify infrastructure (some, for libm functions
and bswap, already has) to make this even simpler to implement.


GCC already has a pass that attempts to track known and earlier computed
lengths of strings, and do various transformations and optimizations based
on that, see the tree-ssa-strlen.c pass.  Most of that you really can't do
at the glibc headers level.

Right.

Ondrej, if you have specific cases that you think ought to be optimized,but aren't, don't hesitate to file bugs for those testcases.

As Jakub noted, we already have significant infrastructure in place tooptimize builtins and chains of builtins. If something is missing, wedefinitely want to know about it so that it can be corrected.


jeff

References:
- Builtin expansion versus headers optimization: Reductions
  - From: OndÅej BÃlka
- Re: Builtin expansion versus headers optimization: Reductions
  - From: Joseph Myers
- Re: Builtin expansion versus headers optimization: Reductions
  - From: Jakub Jelinek

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