From mboxrd@z Thu Jan  1 00:00:00 1970
From: reza@apple.com
To: gcc@gcc.gnu.org
Cc: Reza Yazdani <reza@apple.com>
Subject: bug in aliasing
Date: Wed, 10 Oct 2001 15:56:00 -0000
Message-id: <200110102256.PAA13681@scv1.apple.com>
X-SW-Source: 2001-10/msg00689.html

It seems gcc does not move an invariant local array element out of the 
loop. In the following test "str[2]" is
not moved out of the loop. I went through the interference analysis 
routines and it seems it assumes a store
into any stack variable (m1 array in this case) will interfere with all 
variables allocated on stack,  such as str
in this case.

I was going to find a solution for this problem, but I thought I  would 
ask the experts in the community before I take
a shot at it.

Thanks
Reza Yazdani

Apple Computer


void test()
{
   int str[27];
   int m1[100];
   int k3=0;
   int i;

     for(i='A';i<'Z';i++)
     {
       m1[k3++]=str[2];
     }
}

The assembly code is:

.text
         .align 2
         .globl _test
_test:
         li r2,25
         stwu r1,-560(r1)
         mtctr r2
         li r11,0
         addi r10,r1,144
L9:
         lwz r3,40(r1)       <-- loop invariant
         slwi r2,r11,2
         addi r11,r11,1
         stwx r3,r10,r2
         bdnz L9
         addi r1,r1,560
         blr