free is a killer

[Marc Glisse]

Hello,

this patch teaches gcc that free kills the memory its argument points to. 
The equality test is probably too strict, I guess we can loosen it later 
(unless you have suggestions?).

Note that the corresponding code for BUILT_IN_MEMCPY and others seems 
suspicious to me, it looks like it is testing for equality between a 
pointer and a mem_ref, which is unlikely to happen.

Bootstrap+testsuite on x86_64-unknown-linux-gnu.

2013-10-27  Marc Glisse  <marc.glisse@inria.fr>

 	PR tree-optimization/19831
gcc/
 	* tree-ssa-alias.c (stmt_kills_ref_p_1): Handle BUILT_IN_FREE.

gcc/testsuite/
 	* gcc.dg/tree-ssa/alias-25.c: New file.

-- 
Marc Glisse
-------------- next part --------------
Index: gcc/testsuite/gcc.dg/tree-ssa/alias-25.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/alias-25.c	(revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/alias-25.c	(working copy)
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fdump-tree-optimized" } */
+
+void f (long *p) {
+  *p = 42;
+  p[4] = 42;
+  __builtin_free (p);
+}
+
+/* { dg-final { scan-tree-dump-not "= 42" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */
+

Property changes on: gcc/testsuite/gcc.dg/tree-ssa/alias-25.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 204088)
+++ gcc/tree-ssa-alias.c	(working copy)
@@ -2053,20 +2053,30 @@ stmt_kills_ref_p_1 (gimple stmt, ao_ref
 	}
     }
 
   if (is_gimple_call (stmt))
     {
       tree callee = gimple_call_fndecl (stmt);
       if (callee != NULL_TREE
 	  && DECL_BUILT_IN_CLASS (callee) == BUILT_IN_NORMAL)
 	switch (DECL_FUNCTION_CODE (callee))
 	  {
+	  case BUILT_IN_FREE:
+	    {
+	      tree ptr = gimple_call_arg (stmt, 0);
+	      tree base = ao_ref_base (ref);
+	      if (base && TREE_CODE (base) == MEM_REF
+		  && TREE_OPERAND (base, 0) == ptr)
+		return true;
+	      break;
+	    }
+
 	  case BUILT_IN_MEMCPY:
 	  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);