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From: "oleg.pekar.2017 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/98900] New: Wrong static analyses warning when optimisation
 is on
Date: Sun, 31 Jan 2021 12:23:35 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98900

            Bug ID: 98900
           Summary: Wrong static analyses warning when optimisation is on
           Product: gcc
           Version: 8.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: oleg.pekar.2017 at gmail dot com
  Target Milestone: ---

Created attachment 50095
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D50095&action=3Dedit
Preprocessor output for source file test1.c

gcc version: 8.3.1
system type: RedHat 8.1, Kernel 4.18.0-147.3.1.el8_1.x86_64

Problem: Wrong static analyses warning when optimisation is on.
Input source: attached test1.i
Description: in this code address of a variable local to a block is used
outside of the block. With no optimisation there's no warning while the code
still can cause a problem. But with optimisation static analyses provides a
confusing warning - it complains about a variable not used in the context of
the warning.

Command line with no optimisation: gcc -Wall -save-temps test1.c
Output: nothing

Command line with optimisation: gcc -Wall -save-temps -O2 test1.c
Output:=20
test1.c: In function =E2=80=98main=E2=80=99:
test1.c:11:7: warning: =E2=80=98x=E2=80=99 is used uninitialized in this fu=
nction
[-Wuninitialized]
     g =3D *p;
     ~~^~~~=