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Re: [PATCH] -Wtautological-compare should be quiet on floats

From: Jeff Law <law at redhat dot com>
To: Marek Polacek <polacek at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, Joseph Myers <joseph at codesourcery dot com>, Jason Merrill <jason at redhat dot com>
Date: Wed, 29 Jul 2015 16:44:46 -0600
Subject: Re: [PATCH] -Wtautological-compare should be quiet on floats
Authentication-results: sourceware.org; auth=none
References: <20150729140822 dot GI3335 at redhat dot com>

On 07/29/2015 08:08 AM, Marek Polacek wrote:

As discussed elsewhere, -Wtautological-compare shouldn't warn about
floating-point types because of the way NaN behave.

I've been meaning to commit this one as obvious, but I'm not sure
whether I should also use HONOR_NANS or whether I can safely ignore
that here.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2015-07-29  Marek Polacek  <polacek@redhat.com>

	* c-common.c (warn_tautological_cmp): Bail for float types.

	* c-c++-common/Wtautological-compare-3.c: New test.

I think it comes down to what we think users are going to expect whencompiling code with NaNs disabled.

One camp would probably say "in my code X == X is always true since Idon't have NaNs." The other might say "whether or not to warn on X == Xshould not be dependent on flags such as -ffinite-math-only".

I could easily make a case for either. I'd personally tend to leantowards the latter.


Jeff

Follow-Ups:
- Re: [PATCH] -Wtautological-compare should be quiet on floats
  - From: Marek Polacek

References:
- [PATCH] -Wtautological-compare should be quiet on floats
  - From: Marek Polacek

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