[Bug c++/84816] New: [7.2.0/8.0.1 x86_64] Incorrect code generation if signed overflow

[dlesnikov at hotmail dot com]

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