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Re: [PATCH][RTL ifcvt] PR rtl-optimization/66940: Avoid signed overflow in noce_get_alt_condition

From: Bernd Schmidt <bschmidt at redhat dot com>
To: Kyrill Tkachov <kyrylo dot tkachov at foss dot arm dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
Date: Thu, 2 Jun 2016 11:08:59 +0200
Subject: Re: [PATCH][RTL ifcvt] PR rtl-optimization/66940: Avoid signed overflow in noce_get_alt_condition
Authentication-results: sourceware.org; auth=none
References: <5742E6B2 dot 7050904 at foss dot arm dot com>

On 05/23/2016 01:17 PM, Kyrill Tkachov wrote:

In this PR we end up hitting a signed overflow in noce_get_alt_condition
when we try to
increment or decrement a HOST_WIDE_INT that might be HOST_WIDE_INT_MAX
or HOST_WIDE_INT_MIN.

I've confirmed the overflow by adding an assert before the operation:
gcc_assert (desired_val != HOST_WIDE_INT_MAX);

Don't we have to check for overflow in whatever mode the comparison isin, rather than using HOST_WIDE_INT?

I expect the compile test doesn't actually test anything without somesort of sanitizer enabled for the compiler? If this results in amiscompilation, can you construct an executable test?


Bernd

Follow-Ups:
- Re: [PATCH][RTL ifcvt] PR rtl-optimization/66940: Avoid signed overflow in noce_get_alt_condition
  - From: Kyrill Tkachov

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