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Re: Use MPFR for real.c decimal-string-to-binary conversions (PR 21718)

From: Marc Glisse <marc dot glisse at inria dot fr>
To: "Joseph S. Myers" <joseph at codesourcery dot com>
Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Richard Biener <richard dot guenther at gmail dot com>
Date: Wed, 20 Nov 2013 22:35:45 +0100 (CET)
Subject: Re: Use MPFR for real.c decimal-string-to-binary conversions (PR 21718)
Authentication-results: sourceware.org; auth=none
References: <Pine dot LNX dot 4 dot 64 dot 1311192136190 dot 8742 at digraph dot polyomino dot org dot uk> <CAFiYyc09cVvrDoTy0n9f6wBbFrtXB1s5be3EFCTeCwxGeJ8BpA at mail dot gmail dot com> <Pine dot LNX dot 4 dot 64 dot 1311201816531 dot 28804 at digraph dot polyomino dot org dot uk> <alpine dot DEB dot 2 dot 10 dot 1311202102541 dot 11848 at stedding dot saclay dot inria dot fr> <Pine dot LNX dot 4 dot 64 dot 1311202106580 dot 4182 at digraph dot polyomino dot org dot uk>
Reply-to: gcc-patches at gcc dot gnu dot org

On Wed, 20 Nov 2013, Joseph S. Myers wrote:

On Wed, 20 Nov 2013, Marc Glisse wrote:

On Wed, 20 Nov 2013, Joseph S. Myers wrote:

This patch removes real_sqrt.  (I rather hope that in general little
if any floating-point constant folding is happening on RTL - it
doesn't seem like the sort of thing for which RTL expansion should be
expected to introduce new folding opportunities, and if it does I'd
tend to think that indicates a deficiency in the GIMPLE optimizers.)

Bootstrapped with no regressions on x86_64-unknown-linux-gnu.  OK to
commit?

2013-11-20  Joseph Myers  <joseph@codesourcery.com>

	* real.c (real_sqrt): Remove function.
	* real.h (real_sqrt): Remove prototype.
	* simplify-rtx.c (simplify_const_unary_operation): Do not fold
	SQRT using real_sqrt.


I think you can close PR 55950 with that one.


Thanks for the reference - if you have a case where this code is active
(other than where -fno- options are used to disable GIMPLE constant
propagation etc. artificially, although I couldn't find a suitable
testcase even with such options), could you file a PR in Bugzilla for the
missing GIMPLE optimization that results in this only getting optimized
(or not, after this patch) at the RTL level?

Actually, in my case (sqrt(2.) with -frounding-math), constant propagationwas not wanted. gimple properly avoided it, and now RTL won't do iteither, which is good, no optimization missed.


--
Marc Glisse

References:
- Use MPFR for real.c decimal-string-to-binary conversions (PR 21718)
  - From: Joseph S. Myers
- Re: Use MPFR for real.c decimal-string-to-binary conversions (PR 21718)
  - From: Richard Biener
- Re: Use MPFR for real.c decimal-string-to-binary conversions (PR 21718)
  - From: Joseph S. Myers
- Re: Use MPFR for real.c decimal-string-to-binary conversions (PR 21718)
  - From: Marc Glisse
- Re: Use MPFR for real.c decimal-string-to-binary conversions (PR 21718)
  - From: Joseph S. Myers

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