[PATCH] Fix PR rtl-optimization/24257

[Richard Guenther]

This patch from Steven fixes PR24257.

Bootstrapped and tested on i686-pc-linux-gnu.

Ok for mainline and 4.1?

Thanks,
Richard.


2006-01-10  Steven Bosscher  <steven.bosscher@gmail.com>
	Richard Guenther  <rguenther@suse.de>

	PR rtl-optimization/24257
	* gcse.c (find_moveable_store): Only consider a store movable
	when the SET_SRC of the insn can be assigned to a register.

	* gcc.dg/torture/pr24257.c: New testcase.

Index: gcse.c
===================================================================
--- gcse.c	(revision 109509)
+++ gcse.c	(working copy)
@@ -5647,6 +5647,14 @@ find_moveable_store (rtx insn, int *regs
   if (find_reg_note (insn, REG_EH_REGION, NULL_RTX))
     return;
 
+  /* Make sure that the SET_SRC of this store insns can be assigned to
+     a register, or we will fail later on in replace_store_insn, which
+     assumes that we can do this.  But sometimes the target machine has
+     oddities like MEM read-modify-write instruction.  See for example
+     PR24257.  */
+  if (!can_assign_to_reg_p (SET_SRC (set)))
+    return;
+
   ptr = ldst_entry (dest);
   if (!ptr->pattern_regs)
     ptr->pattern_regs = extract_mentioned_regs (dest);


/* { dg-do compile } */
/* { dg-options "-O -fgcse -fgcse-sm" } */

typedef struct A {
    int buf, left;
} A;

static void flush(A *s, int n)
{
    s->buf <<= n;

    while (s->left < 32) {
        s->buf <<= 8;
        s->left += 8;
    }

    s->buf=0;
}

void oof(A *s, int n)
{
    s->buf = n;
    s->left = n;

    flush(s, n);
}