Re: [RFA][PATCH] Minor fix to aliasing machinery

[Marc Glisse <marc dot glisse at inria dot fr>]

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):

! { dg-do run }
! { dg-options "-fbackslash" }

  implicit none
  character(kind=1,len=3) :: s1(3)

  s1 = [ "abc", "def", "ghi" ]

  if (any (cshift (s1, -1) /= [ s1(3), s1(1:2) ])) call abort

end


we end up with a double array_ref, one of variable index, and 
get_ref_base_and_extent signals that by returning as size the size of the 
whole declaration (the double-array). However, 
ao_ref_init_from_ptr_and_size happily ignores the last two parameters of 
get_ref_base_and_extent and continues as if nothing was wrong (I don't 
know how to easily check that something went wrong either). Whether we 
think this is a good/bad patch for memcpy, we have a latent bug that the 
recent patches are making more visible.

--
Marc Glisse

Index: testsuite/gcc.dg/tree-ssa/alias-26.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/alias-26.c	(revision 0)
+++ testsuite/gcc.dg/tree-ssa/alias-26.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: testsuite/gcc.dg/tree-ssa/alias-26.c
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Added: svn:eol-style
## -0,0 +1 ##
+native
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Added: svn:keywords
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Index: tree-ssa-alias.c
===================================================================
--- tree-ssa-alias.c	(revision 204199)
+++ tree-ssa-alias.c	(working copy)
@@ -1982,23 +1982,24 @@ 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.  */
@@ -2071,37 +2072,47 @@ 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)
+		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)
 		{