[RFA][PATCH] Minor fix to aliasing machinery

[Marc Glisse]

[Discussion started in http://gcc.gnu.org/ml/gcc-patches/2013-10/msg02472.html ]

On Wed, 30 Oct 2013, Marc Glisse wrote:

> On Wed, 30 Oct 2013, Richard Biener wrote:
>
>> Btw, get_addr_base_and_unit_offset may also return an offsetted
>> MEM_REF (from &MEM [p_3, 17] for example).  As we are interested in
>> pointers this could be handled by not requiring a memory reference
>> but extracting the base address and offset, covering more cases.
>
> I tried the attached patch, and it almost worked, except for one fortran 
> testcase (widechar_intrinsics_10.f90):

Now that ao_ref_init_from_ptr_and_size has been fixed, the following patch 
passes bootstrap+testsuite (default languages) on 
x86_64-unknown-linux-gnu.

2013-11-06  Marc Glisse  <marc.glisse@inria.fr>
 	    Jeff Law  <law@redhat.com>

gcc/
 	* tree-ssa-alias.c (stmt_kills_ref_p_1): Use
 	ao_ref_init_from_ptr_and_size for builtins.

gcc/testsuite/
 	* gcc.dg/tree-ssa/alias-27.c: New testcase.

-- 
Marc Glisse
-------------- next part --------------
Index: gcc/testsuite/gcc.dg/tree-ssa/alias-27.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/alias-27.c	(revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/alias-27.c	(working copy)
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-tree-optimized" } */
+
+void f (long *p) {
+  *p = 42;
+  p[4] = 42;
+  __builtin_memset (p, 0, 100);
+}
+
+/* { dg-final { scan-tree-dump-not "= 42" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */

Property changes on: gcc/testsuite/gcc.dg/tree-ssa/alias-27.c
___________________________________________________________________
Added: svn:keywords
## -0,0 +1 ##
+Author Date Id Revision URL
\ No newline at end of property
Added: svn:eol-style
## -0,0 +1 ##
+native
\ No newline at end of property
Index: gcc/tree-ssa-alias.c
===================================================================
--- gcc/tree-ssa-alias.c	(revision 204453)
+++ gcc/tree-ssa-alias.c	(working copy)
@@ -2001,23 +2001,24 @@ stmt_may_clobber_ref_p (gimple stmt, tre
   return stmt_may_clobber_ref_p_1 (stmt, &r);
 }
 
 /* If STMT kills the memory reference REF return true, otherwise
    return false.  */
 
 static bool
 stmt_kills_ref_p_1 (gimple stmt, ao_ref *ref)
 {
   /* For a must-alias check we need to be able to constrain
-     the access properly.  */
-  ao_ref_base (ref);
-  if (ref->max_size == -1)
+     the access properly.
+     FIXME: except for BUILTIN_FREE.  */
+  if (!ao_ref_base (ref)
+      || ref->max_size == -1)
     return false;
 
   if (gimple_has_lhs (stmt)
       && TREE_CODE (gimple_get_lhs (stmt)) != SSA_NAME
       /* The assignment is not necessarily carried out if it can throw
 	 and we can catch it in the current function where we could inspect
 	 the previous value.
 	 ???  We only need to care about the RHS throwing.  For aggregate
 	 assignments or similar calls and non-call exceptions the LHS
 	 might throw as well.  */
@@ -2090,37 +2091,47 @@ stmt_kills_ref_p_1 (gimple stmt, ao_ref
 	  case BUILT_IN_MEMPCPY:
 	  case BUILT_IN_MEMMOVE:
 	  case BUILT_IN_MEMSET:
 	  case BUILT_IN_MEMCPY_CHK:
 	  case BUILT_IN_MEMPCPY_CHK:
 	  case BUILT_IN_MEMMOVE_CHK:
 	  case BUILT_IN_MEMSET_CHK:
 	    {
 	      tree dest = gimple_call_arg (stmt, 0);
 	      tree len = gimple_call_arg (stmt, 2);
-	      tree base = NULL_TREE;
-	      HOST_WIDE_INT offset = 0;
+	      tree rbase = ref->base;
+	      HOST_WIDE_INT roffset = ref->offset;
 	      if (!host_integerp (len, 0))
 		return false;
-	      if (TREE_CODE (dest) == ADDR_EXPR)
-		base = get_addr_base_and_unit_offset (TREE_OPERAND (dest, 0),
-						      &offset);
-	      else if (TREE_CODE (dest) == SSA_NAME)
-		base = dest;
-	      if (base
-		  && base == ao_ref_base (ref))
+	      ao_ref dref;
+	      ao_ref_init_from_ptr_and_size (&dref, dest, len);
+	      tree base = ao_ref_base (&dref);
+	      HOST_WIDE_INT offset = dref.offset;
+	      if (!base || dref.size == -1)
+		return false;
+	      if (TREE_CODE (base) == MEM_REF)
+		{
+		  if (TREE_CODE (rbase) != MEM_REF)
+		    return false;
+		  // Compare pointers.
+		  offset += BITS_PER_UNIT
+			    * TREE_INT_CST_LOW (TREE_OPERAND (base, 1));
+		  roffset += BITS_PER_UNIT
+			     * TREE_INT_CST_LOW (TREE_OPERAND (rbase, 1));
+		  base = TREE_OPERAND (base, 0);
+		  rbase = TREE_OPERAND (rbase, 0);
+		}
+	      if (base == rbase)
 		{
-		  HOST_WIDE_INT size = TREE_INT_CST_LOW (len);
-		  if (offset <= ref->offset / BITS_PER_UNIT
-		      && (offset + size
-		          >= ((ref->offset + ref->max_size + BITS_PER_UNIT - 1)
-			      / BITS_PER_UNIT)))
+		  HOST_WIDE_INT size = BITS_PER_UNIT * TREE_INT_CST_LOW (len);
+		  if (offset <= roffset
+		      && offset + size >= (roffset + ref->max_size))
 		    return true;
 		}
 	      break;
 	    }
 
 	  case BUILT_IN_VA_END:
 	    {
 	      tree ptr = gimple_call_arg (stmt, 0);
 	      if (TREE_CODE (ptr) == ADDR_EXPR)
 		{