https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108720
Bug ID: 108720
Summary: INT_MIN * -1 is incorrect
Product: gcc
Version: 11.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: amk7r at mtmail dot mtsu.edu
Target Milestone: ---
Created attachment 54434
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54434&action=edit
Attached is a file with the source code (.c) and the preprocessed file (.i)
Version of GCC: 11.3.0
System type: Ubuntu 22.04.1 LTS
Options given when GCC was configured/built: ../src/configure -v
--with-pkgversion='Ubuntu 11.3.0-1ubuntu1~22.04'
--with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-11
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-11-xKiWfi/gcc-11-11.3.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-11-xKiWfi/gcc-11-11.3.0/debian/tmp-gcn/usr
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=2
Complete command line that triggers the bug: gcc err_file.c
The compiler output (error messages, warnings, ect.): n/a; there were no errors
or warnings
Expected behavior:
The program should print out the value of y, and then print out “true 4”
because -INT_MIN is equal to INT_MIN, which is less than 0.
Actual behavior:
The program prints out the value of y, and then prints out “true 2.”
Case 1: y>= 0. "true 1" should not be printed because y is INT_MIN. -> Test
Pass
Case 2: (x-1)>= 0. "true 2" should not be printed because x is INT_MIN. ->
Test Fail
o INT_MIN * -1 = INT_MIN.
Case 3: (x-1)>= zero. "true 3" should not be printed because x is INT_MIN.
-> Test Pass
o INT_MIN * -1 = INT_MIN and int zero has 0
Case 4: (x-1)< 0. "true 4" should be printed because x is INT_MIN.
o INT_MIN * -1 = INT_MIN and INT_MIN is less than 0 -> Test Fail
More information:
If you translate the C code into assembly code using the command “gcc -s
err_file.c,” and check the .L2 block:
In .L2:
The assembly code should be:
#equivalent c code
cmpl $0, -8(%rbp) #because it has the result of x * -1
if ((x*-1)>=0)
js .L3 #instead of jg .L3
Explanation:
* x *-1 is INT_MIN.
* “jg” instruction will skip the statement in “if block” if (x*-1) or
INT_MIN is greater than 0.
* Since, (x*-1) or INT_MIN is not greater than 0, the statement in the
“if block” is printed (“true 2”).
* But “true 2” should only be printed if (x*-1) or INT_MIN is greater
than or equal to 0 (check c code line 9).
* In this case, doing “js .L3” would make more sense and will give the
expected result.
