[Bug c/59812] New: Missing aggressive loop optimization warning

[ppluzhnikov at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59812

            Bug ID: 59812
           Summary: Missing aggressive loop optimization warning
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppluzhnikov at google dot com

Google ref: b/12015772

The following source:

int x[4];
int foo (int a)
{
 int n = a ? 1 : 2;
 int i;
 for(i = 0; i < 4 + n; i++ )
   x[i]++;
 return 0;
}


compiles into infinite loop due to aggressive loop optimization,
but produces no warnings with

g++ (GCC) 4.9.0 20140110 (experimental)

g++ -c -O2 -Wall -Wextra t.c && objdump -d t.o

t.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <_Z3fooi>:
   0:   b8 00 00 00 00          mov    $0x0,%eax
   5:   83 00 01                addl   $0x1,(%rax)
   8:   48 83 c0 04             add    $0x4,%rax
   c:   eb f7                   jmp    5 <_Z3fooi+0x5>


It would be much nicer to end-user to emit compile time warning here.