[llvm-bugs] [Bug 37766] New: Uninitialized bool values accessed by optimizer

via llvm-bugs llvm-bugs at lists.llvm.org
Mon Jun 11 05:59:02 PDT 2018


            Bug ID: 37766
           Summary: Uninitialized bool values accessed by optimizer
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: tss at iki.fi
                CC: llvm-bugs at lists.llvm.org

This happens with v3.8.0 and in 6.0.0 git version from 13 Sep 2017, so I'd
expect it to still happen with newer versions. Using valgrind shows that the
"set" variable is accessed, even though ret==false always so it's not supposed
to be accessed. Doesn't happen if foo() is in the same .c file.

/* test2.c */
#include <stdbool.h>
_Bool foo(_Bool *value_r)
        return false;

/* test.c */
#include <stdio.h>
#include <stdbool.h>

_Bool foo(_Bool *value_r);

int main(void)
        bool set;
        bool ret = foo(&set);
        if (ret && set)
        if (!ret)
                return 1;
        return 0;

clang test2.c -c -o test2.o
clang -O2 -g test.c test2.o -o test
valgrind ./test

==28241== Conditional jump or move depends on uninitialised value(s)
==28241==    at 0x4004E9: main (test.c:10)

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