https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86940
Bug ID: 86940
Summary: False positive with -Wuninitialized
Product: gcc
Version: 8.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: aerkiaga6 at gmail dot com
Target Milestone: ---
Created attachment 44532
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44532&action=edit
Preprocessed source
Compiling the code with the following command:
gcc -v -save-temps -Wall -O test.c
Gives this output:
gcc -v -save-temps -Wall -O test.c
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc/x86_64-pc-linux-gnu/8.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-8.2.0/configure --enable-languages=c,c++
Thread model: posix
gcc version 8.2.0 (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-O' '-mtune=generic'
'-march=x86-64'
/usr/local/libexec/gcc/x86_64-pc-linux-gnu/8.2.0/cc1 -E -quiet -v -imultiarch
x86_64-linux-gnu test.c -mtune=generic -march=x86-64 -Wall -O -fpch-preprocess
-o test.i
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/include
/usr/local/include
/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-O' '-mtune=generic'
'-march=x86-64'
/usr/local/libexec/gcc/x86_64-pc-linux-gnu/8.2.0/cc1 -fpreprocessed test.i
-quiet -dumpbase test.c -mtune=generic -march=x86-64 -auxbase test -O -Wall
-version -o test.s
GNU C17 (GCC) version 8.2.0 (x86_64-pc-linux-gnu)
compiled by GNU C version 8.2.0, GMP version 6.1.2, MPFR version 4.0.1,
MPC version 1.1.0, isl version isl-0.19-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C17 (GCC) version 8.2.0 (x86_64-pc-linux-gnu)
compiled by GNU C version 8.2.0, GMP version 6.1.2, MPFR version 4.0.1,
MPC version 1.1.0, isl version isl-0.19-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 82490e2e2080530dcab0165c2e5082fa
test.c: In function ‘main’:
test.c:15:20: warning: ‘str’ may be used uninitialized in this function
[-Wmaybe-uninitialized]
if(initialize) free(str);
^~~~~~~~~
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-O' '-mtune=generic'
'-march=x86-64'
/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/bin/as
-v --64 -o test.o test.s
GNU assembler version 2.31.1 (x86_64-pc-linux-gnu) using BFD version (GNU
Binutils) 2.31.1
COMPILER_PATH=/usr/local/libexec/gcc/x86_64-pc-linux-gnu/8.2.0/:/usr/local/libexec/gcc/x86_64-pc-linux-gnu/8.2.0/:/usr/local/libexec/gcc/x86_64-pc-linux-gnu/:/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/:/usr/local/lib/gcc/x86_64-pc-linux-gnu/:/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/bin/
LIBRARY_PATH=/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/:/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../lib64/:/lib/x86_64-linux-gnu/:/lib/../lib64/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib64/:/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/lib/:/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-O' '-mtune=generic'
'-march=x86-64'
/usr/local/libexec/gcc/x86_64-pc-linux-gnu/8.2.0/collect2 -plugin
/usr/local/libexec/gcc/x86_64-pc-linux-gnu/8.2.0/liblto_plugin.so
-plugin-opt=/usr/local/libexec/gcc/x86_64-pc-linux-gnu/8.2.0/lto-wrapper
-plugin-opt=-fresolution=test.res -plugin-opt=-pass-through=-lgcc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s
--eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2
/usr/lib/x86_64-linux-gnu/crt1.o /usr/lib/x86_64-linux-gnu/crti.o
/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/crtbegin.o
-L/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0
-L/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../lib64
-L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu
-L/usr/lib/../lib64
-L/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../x86_64-pc-linux-gnu/lib
-L/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../.. test.o -lgcc
--as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed
/usr/local/lib/gcc/x86_64-pc-linux-gnu/8.2.0/crtend.o
/usr/lib/x86_64-linux-gnu/crtn.o
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-O' '-mtune=generic'
'-march=x86-64'
GCC complains that 'str' may be uninitialized, which is not possible.
Requirements for triggering the bug include compiling with -O1 or greater.
Omitting this flag gives no warning. Also, no warning is produced if func()
returns just a constant value.
It appears like GCC thinks that func() may have some side effects which change
the value of initialize, which is not the case.
Also, while substituting the call to free() with another expression with str
(e.g. puts(str) or printf("%p", str)) does not remove the warning, the call to
malloc() turns out to be important. Replacing it with a constant value makes
the warning dissapear, regardless of the expression used in place of free().
