This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Aliasing: look through pointer's def stmt


On Tue, 29 Oct 2013, Richard Biener wrote:

For the POINTER_PLUS_EXPR offset argument you should use
int_cst_value () to access it (it will unconditionally sign-extend)
and use host_integerp (..., 0).  That leaves the overflow possibility
in place (and you should multiply by BITS_PER_UNIT) which we
ignore in enough other places similar to this to ignore ...

Like this? (passes bootstrap+testsuite on x86_64-linux-gnu)

2013-10-30  Marc Glisse  <marc.glisse@inria.fr>

gcc/
	* tree-ssa-alias.c (ao_ref_init_from_ptr_and_size): Look for a
	POINTER_PLUS_EXPR in the defining statement.

gcc/testsuite/
	* gcc.dg/tree-ssa/alias-24.c: New file.


--
Marc Glisse
Index: gcc/testsuite/gcc.dg/tree-ssa/alias-24.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/alias-24.c	(revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/alias-24.c	(working copy)
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+void f (const char *c, int *i)
+{
+  *i = 42;
+  __builtin_memcpy (i + 1, c, sizeof (int));
+  if (*i != 42) __builtin_abort();
+}
+
+extern void keepit ();
+void g (const char *c, int *i)
+{
+  *i = 33;
+  __builtin_memcpy (i - 1, c, 3 * sizeof (int));
+  if (*i != 33) keepit();
+}
+
+/* { dg-final { scan-tree-dump-not "abort" "optimized" } } */
+/* { dg-final { scan-tree-dump "keepit" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
+

Property changes on: gcc/testsuite/gcc.dg/tree-ssa/alias-24.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 204188)
+++ gcc/tree-ssa-alias.c	(working copy)
@@ -567,20 +567,29 @@ void
 ao_ref_init_from_ptr_and_size (ao_ref *ref, tree ptr, tree size)
 {
   HOST_WIDE_INT t1, t2;
   ref->ref = NULL_TREE;
   if (TREE_CODE (ptr) == SSA_NAME)
     {
       gimple stmt = SSA_NAME_DEF_STMT (ptr);
       if (gimple_assign_single_p (stmt)
 	  && gimple_assign_rhs_code (stmt) == ADDR_EXPR)
 	ptr = gimple_assign_rhs1 (stmt);
+      else if (is_gimple_assign (stmt)
+	       && gimple_assign_rhs_code (stmt) == POINTER_PLUS_EXPR
+	       && host_integerp (gimple_assign_rhs2 (stmt), 0)
+	       && (t1 = int_cst_value (gimple_assign_rhs2 (stmt))) >= 0)
+	{
+	  ao_ref_init_from_ptr_and_size (ref, gimple_assign_rhs1 (stmt), size);
+	  ref->offset += 8 * t1;
+	  return;
+	}
     }
 
   if (TREE_CODE (ptr) == ADDR_EXPR)
     ref->base = get_ref_base_and_extent (TREE_OPERAND (ptr, 0),
 					 &ref->offset, &t1, &t2);
   else
     {
       ref->base = build2 (MEM_REF, char_type_node,
 			  ptr, null_pointer_node);
       ref->offset = 0;

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]