[PATCH] PR35258: Prevent CSE from generating overlapping memmoves

Andreas Krebbel Andreas.Krebbel@de.ibm.com
Mon Feb 25 13:43:00 GMT 2008


Hi,

> It looks like you can use nonoverlapping_memrefs_p from alias.c
> instead of adding cse_mem_cannot_overlap_p?

I thought that one is only supposed to be used from within alias.c but
actually I don't see a reason for that.

So here is the patch.

Bootstrapped and regtested on x86_64, s390 and s390x.

OK for mainline and 4.3?

Bye,

-Andreas-

2008-02-25  Andreas Krebbel  <krebbel1@de.ibm.com>

	* cse.c (cse_insn): Avoid creation of overlapping MEMs.
	* alias.c (nonoverlapping_memrefs_p): Export for use in other modules.
	* alias.h (nonoverlapping_memrefs_p): Likewise.

2008-02-25  Andreas Krebbel  <krebbel1@de.ibm.com>

	* gcc.dg/pr35258.c: New testcase.

Index: gcc/cse.c
===================================================================
*** gcc/cse.c.orig	2008-02-22 10:46:18.000000000 +0100
--- gcc/cse.c	2008-02-25 09:15:34.000000000 +0100
*************** cse_insn (rtx insn, rtx libcall_insn)
*** 4753,4758 ****
--- 4753,4775 ----
  	      src_elt_cost = MAX_COST;
  	    }
  
+ 	  /* Avoid creation of overlapping memory moves.  */
+ 	  if (MEM_P (trial) && MEM_P (SET_DEST (sets[i].rtl)))
+ 	    {
+ 	      rtx src, dest;
+ 
+ 	      /* BLKmode moves are not handled by cse anyway.  */
+ 	      if (GET_MODE (trial) == BLKmode)
+ 		break;
+ 
+ 	      src = canon_rtx (trial);
+ 	      dest = canon_rtx (SET_DEST (sets[i].rtl));
+ 
+ 	      if (!MEM_P (src) || !MEM_P (dest)
+ 		  || !nonoverlapping_memrefs_p (src, dest))
+ 		break;
+ 	    }
+ 
  	  /* We don't normally have an insn matching (set (pc) (pc)), so
  	     check for this separately here.  We will delete such an
  	     insn below.
Index: gcc/testsuite/gcc.dg/pr35258.c
===================================================================
*** /dev/null	1970-01-01 00:00:00.000000000 +0000
--- gcc/testsuite/gcc.dg/pr35258.c	2008-02-22 10:47:55.000000000 +0100
***************
*** 0 ****
--- 1,28 ----
+ /* { dg-do run } */
+ /* { dg-options "-O1" } */
+ 
+ extern void *memcpy (void *, const void *, __SIZE_TYPE__);
+ extern int memcmp (const void *, const void *, __SIZE_TYPE__);
+ extern void abort(void);
+ 
+ char str[9] = "1234";
+ 
+ void
+ bar (void)
+ {
+   unsigned int temp;
+   char *p = &str[2];
+ 
+   memcpy (&temp, &str[1], 4);
+   memcpy (p, &temp, 4);
+   str[1] = '.';
+ }
+ 
+ int main()
+ {
+   bar();
+   if (memcmp (str, "1.234", 5) != 0)
+     abort ();
+ 
+   return 0;
+ }
Index: gcc/alias.c
===================================================================
*** gcc/alias.c.orig	2007-10-26 10:35:40.000000000 +0200
--- gcc/alias.c	2008-02-25 09:11:51.000000000 +0100
*************** static int aliases_everything_p (const_r
*** 164,170 ****
  static bool nonoverlapping_component_refs_p (const_tree, const_tree);
  static tree decl_for_component_ref (tree);
  static rtx adjust_offset_for_component_ref (tree, rtx);
- static int nonoverlapping_memrefs_p (const_rtx, const_rtx);
  static int write_dependence_p (const_rtx, const_rtx, int);
  
  static void memory_modified_1 (rtx, const_rtx, void *);
--- 164,169 ----
*************** adjust_offset_for_component_ref (tree x,
*** 1976,1982 ****
  /* Return nonzero if we can determine the exprs corresponding to memrefs
     X and Y and they do not overlap.  */
  
! static int
  nonoverlapping_memrefs_p (const_rtx x, const_rtx y)
  {
    tree exprx = MEM_EXPR (x), expry = MEM_EXPR (y);
--- 1975,1981 ----
  /* Return nonzero if we can determine the exprs corresponding to memrefs
     X and Y and they do not overlap.  */
  
! int
  nonoverlapping_memrefs_p (const_rtx x, const_rtx y)
  {
    tree exprx = MEM_EXPR (x), expry = MEM_EXPR (y);
Index: gcc/alias.h
===================================================================
*** gcc/alias.h.orig	2007-08-28 08:51:49.000000000 +0200
--- gcc/alias.h	2008-02-25 09:10:48.000000000 +0100
*************** extern alias_set_type get_varargs_alias_
*** 28,33 ****
--- 28,34 ----
  extern alias_set_type get_frame_alias_set (void);
  extern bool component_uses_parent_alias_set (const_tree);
  extern bool alias_set_subset_of (alias_set_type, alias_set_type);
+ extern int nonoverlapping_memrefs_p (const_rtx, const_rtx);
  
  /* This alias set can be used to force a memory to conflict with all
     other memories, creating a barrier across which no memory reference



More information about the Gcc-patches mailing list