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Subject: [Bug c++/98829] New: Different results with -O3 and custom quiet NaN
Date: Mon, 25 Jan 2021 22:32:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98829

            Bug ID: 98829
           Summary: Different results with -O3 and custom quiet NaN
           Product: gcc
           Version: 10.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gnu at nemanjaboric dot com
  Target Milestone: ---

Created attachment 50047
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D50047&action=3Dedit
Example of the code giving different results

Hi, see the attached code which generates the different code with -O3 (comp=
iled
with various GCC version). Two workarounds are commented in the code: to use
`std::isnan` and to copy the source object.

I couldn't find anything undefined that I'm doing here but I might be wrong.

-ffast-math _is not_ used. Just -O3 yields different result:
https://www.godbolt.org/z/nxPd8W=