https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66876
Bug ID: 66876
Summary: vrp: changing unsigned to signed comparison
Product: gcc
Version: 5.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: konstantin.vladimirov at gmail dot com
Target Milestone: ---
Minimized test case (note explicit unsigned long cast):
---
#include <stdlib.h>
int a = 0xecfb39f5;
unsigned short *d = (unsigned short *) &a;
int
main (void)
{
if ((unsigned long) (65536 * d[1] + d[0]) < (1UL << 28))
{
abort ();
}
return 0;
}
---
Compiler version:
---
$ ~/x86-toolchain-5.1/bin/gcc -v
Using built-in specs.
COLLECT_GCC=/home/tilir/x86-toolchain-5.1/bin/gcc
COLLECT_LTO_WRAPPER=/home/tilir/x86-toolchain-5.1/libexec/gcc/x86_64-unknown-linux-gnu/5.1.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-5.1-src/gcc_5_1_0_release/configure
--enable-languages=c,c++ --prefix=/home/tilir/x86-toolchain-5.1/
Thread model: posix
gcc version 5.1.0 (GCC)
---
$ ~/x86-toolchain-5.1/bin/gcc -O2 test.c
$ ./a.out
Aborted
but
$ ~/x86-toolchain-5.1/bin/gcc -O2 test.c -fno-tree-vrp
$ ./a.out
Everything is ok.
Before VRP:
_9 = (unsigned int) _8;
if (_9 <= 268435455)
goto <bb 3>;
else
goto <bb 4>;
On VRP stage:
_8 : --> single use.
_9 = (unsigned int) _8;
_9 : --> single use.
if (_9 <= 268435455)
After VRP:
if (_8 <= 268435455)
goto <bb 3>;
else
goto <bb 4>;
By C11 standard, the rank of unsigned long is equal to rank of long and higher,
then rank of int, so integer promotions here should make unsigned long from
both sides.
