[Bug target/40457] use stm and ldm to access consecutive memory words

[carrot at google dot com]

------- Comment #1 from carrot at google dot com  2009-06-16 09:11 -------
Created an attachment (id=18005)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18005&action=view)
test case

For this function

void foo(int* p)
{
  p[0] = 1;
  p[1] = 2;
}

gcc generates:

mov     r1, #1
mov     r3, #2
str     r1, [r0]
str     r3, [r0, #4]
bx      lr

We use one stm instruction to replace two str instructions.

For the second case:

int bar(int* p)
{
  int x = p[0] + p[1];
  return x;
}

gcc generates:

ldr     r2, [r0, #4]
ldr     r3, [r0]
add     r0, r2, r3
bx      lr

In this case we can use on ldm to replace the two ldr instructions.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40457