[Bug c/58808] New: Unnecessary MOV instruction generated

[smeeze at catlover dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58808

            Bug ID: 58808
           Summary: Unnecessary MOV instruction generated
           Product: gcc
           Version: 4.6.2
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: smeeze at catlover dot com

GCC sometimes generates an unnecessary MOV operation.

For example gcc -S test.c -masm=intel
on this code:
#include <stdio.h>
int main(){
    int i = 2;
    int b;
    b = i + i + i;
    printf("%d", b);
    return 0;
}
Generates this


mov    DWORD PTR [esp+28], 2
    mov    eax, DWORD PTR [esp+28]
    add    eax, eax
    add    eax, DWORD PTR [esp+28]
    mov    DWORD PTR [esp+24], eax
    mov    eax, DWORD PTR [esp+24] ;<-- Why?? The last instruction does not
affect EAX
    mov    DWORD PTR [esp+4], eax 
    mov    DWORD PTR [esp], OFFSET FLAT:LC0
    call    _printf