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From: "krister.walfridsson at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/94392] New: Infinite loops are optimized away for C99
Date: Sun, 29 Mar 2020 21:13:56 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94392

            Bug ID: 94392
           Summary: Infinite loops are optimized away for C99
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: krister.walfridsson at gmail dot com
  Target Milestone: ---

Created attachment 48141
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D48141&action=3Dedit
Source code reproducing the issue

John Regehr noticed on twitter
(https://twitter.com/johnregehr/status/1244335355509129216) that trunk GCC
removes infinite loops for C99, as can be seen by
  gcc -O3 -std=3Dc99 fermat.c

This behavior was introduced by the introduction of -ffinite-loops being
enabled at -O2. This is fine for C11, but infinite loops do not invoke
undefined behavior in C99, so the optimization should not be enabled per
default for -std=3Dc99.=