https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84816
Bug ID: 84816
Summary: [7.2.0/8.0.1 x86_64] Incorrect code generation if
signed overflow
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: dlesnikov at hotmail dot com
Target Milestone: ---
Hello!
# g++-7 --version
g++-7 (Ubuntu 7.2.0-8ubuntu3.1~16.04.york0) 7.2.0
# g++-8 --version
g++-8 (Ubuntu 8-20180218-1ubuntu1~16.04.york0) 8.0.1 20180218 (experimental)
[trunk revision 257787]
c++ code <sigover.cpp>:
#include <stdio.h>
class C1 {};
int main(void)
{
C1 c1;
int a = 0x7FFFFFFA;
for(int i=0; i<10; i++)
printf("%d\n", ++a);
return 0;
}
g++-7[8] -O2 -S sigover.cpp
the loop assembler code with error:
.L2:
addl $1, %ebx
movl $.LC0, %esi
movl $1, %edi
movl %ebx, %edx
xorl %eax, %eax
call __printf_chk
jmp .L2 <-- infinite loop
.cfi_endproc
.LFE30:
g++-7[8] -O1 -S sigover.cpp
the loop assembler code without error:
.L2:
addl $1, %ebx
movl %ebx, %edx
movl $.LC0, %esi
movl $1, %edi
movl $0, %eax
call __printf_chk
cmpl $-2147483644, %ebx <-- check the end of loop
jne .L2
movl $0, %eax
popq %rbx
.cfi_def_cfa_offset 8
ret
.cfi_endproc
.LFE30:
if comment 1st line in main:
// C1 c1;
then g++-7 -O2 correctly generates the code
but g++-8 -O2 still makes an infinite loop
