Error in gcc version 2.96 20000731

[Kjeld Borch Egevang <kjelde@mips.com>]

Hi all.

I discovered an optimization error in the current gcc for MIPS.

When I compile the code below with -O2 it clears the code-field just 
after setting it. The instructions are mixed up. It works fine with -O1 
and -O0.

If the "//" is removed in front of the first printf, it works too.


/Kjeld

--------------- cut here -----------------
#include <stdio.h>


typedef struct rtx_def
{
 short code;
 int dummy;
} rtx;


void put_code (rtx *rt, short code)
{
 register int length;

 length = 1;
 for (; length >= 0; length--)
   ((int *) rt)[length] = 0;

 // printf("put_code before\n");
 rt->code = code;
 printf("put_code after, code=%d %d\n", code, rt->code);
}


int main()
{
 rtx rt;

 put_code(&rt, 5);
 printf("gen_rtx, code=%d\n", rt.code);
}
--------------- cut here -----------------


The assembler looks like:

       .rdata
       .align  2
$LC0:
       .ascii  "put_code after, code=%d %d\n\000"
       .text
       .align  2
       .globl  put_code
       .ent    put_code
       .type    put_code,@function
put_code:
       .frame  $sp,32,$31              # vars= 0, regs= 2/0, args= 16, 
extra= 8
       .mask   0x90000000,-4
       .fmask  0x00000000,0
       .set    noreorder
       .cpload $25
       .set    reorder
       subu    $sp,$sp,32
       .cprestore 16
       move    $2,$5
       sll     $2,$2,16
       sra     $2,$2,16
       move    $5,$2
       la      $3,$LC0
       sw      $31,28($sp)
       sw      $28,24($sp)
       move    $6,$5
       sh      $2,0($4)     <----- sets code field
       sw      $0,4($4)     <----- clears structure
       sw      $0,0($4)     <----- clears structure
       move    $4,$3
       la      $25,printf
       jal     $31,$25
       lw      $31,28($sp)
       #nop
       .set    noreorder
       .set    nomacro
       j       $31
       addu    $sp,$sp,32
       .set    macro
       .set    reorder

       .end    put_code