[Bug c/21171] New: Generates wrong code (w/ optimization) when copying data from a table to a table in a structure

["sami dot kantoluoto at embedtronics dot fi" <gcc-bugzilla@gcc.gnu.org>]

Compiling the test code with optimizations enabled generates invalid code. Data
gets read from the source table but gets not written to the destination.

Test code:
/* start of test.c */

/* compile: arm-elf-gcc -Os -c -o test.o test.c */
/*    dump: arm-elf-objdump -D test.o | more    */

typedef unsigned int u_int32_t;
typedef unsigned char u_int8_t;

#define AIC_VECTORS     32
        
typedef volatile struct AT91RM9200_AIC {
  u_int32_t             SVR[AIC_VECTORS];
} AT91RM9200_AIC_t;
         
typedef volatile struct AT91RM9200_regs {
  AT91RM9200_AIC_t      AIC;
} AT91RM9200_regs_t;
            
#define CPUReg          ((AT91RM9200_regs_t*)0xFFF00000)
        
extern const u_int32_t __IntTable[AIC_VECTORS];
        
int main()
{
  int c;
  AT91RM9200_AIC_t *aic = &CPUReg->AIC;
            
  for (c=0; c < AIC_VECTORS; c++) {
    aic->SVR[c] = __IntTable[c];
  }

  return 0;
}
/* end of test.c */

objdump output:

test.o:     file format elf32-littlearm
        
Disassembly of section .text:
        
00000000 <main>:
   0:   e59f2014        ldr     r2, [pc, #20]   ; 1c <.text+0x1c>
   4:   e59f3014        ldr     r3, [pc, #20]   ; 20 <.text+0x20>
   8:   e2822004        add     r2, r2, #4      ; 0x4
   c:   e1520003        cmp     r2, r3
  10:   1affffff        bne     4 <main+0x4>
  14:   e3a00000        mov     r0, #0  ; 0x0
  18:   e12fff1e        bx      lr

As you can see, there is no store (str) instruction at all. Code just goes
through the __IntTable[] but does nothing useful.

-- 
           Summary: Generates wrong code (w/ optimization) when copying data
                    from a table to a table in a structure
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P1
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sami dot kantoluoto at embedtronics dot fi
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i386-unknown-netbsdelf2.0
  GCC host triplet: i386-unknown-netbsdelf2.0
GCC target triplet: arm-unknown-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21171