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From: "eggert at cs dot ucla.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug analyzer/107565] New: -Wanalyzer-use-of-uninitialized-value
 false positive with rdrand
Date: Tue, 08 Nov 2022 01:15:42 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107565

            Bug ID: 107565
           Summary: -Wanalyzer-use-of-uninitialized-value false positive
                    with rdrand
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: analyzer
          Assignee: dmalcolm at gcc dot gnu.org
          Reporter: eggert at cs dot ucla.edu
  Target Milestone: ---

Created attachment 53846
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D53846&action=3Dedit
test program illustrating the -fanalyzer false positive

This is gcc (GCC) 12.2.1 20220819 (Red Hat 12.2.1-2) on x86-64. Compile the
attached program with the command:

gcc -O2 -mrdrnd -fanalyzer -S t.c

GCC says "warning: use of uninitialized value =E2=80=98x=E2=80=99 [CWE-457]
[-Wanalyzer-use-of-uninitialized-value]". This is a false positive, as x ca=
nnot
possibly be uninitialized. Apparently -fanalyzer is confused about how
__builtin_ia32_rdrand64_step works.

GCC 11.3.0 does not issue this diagnostic, so this is a regression.=