re PR tree-optimization/19831 (Missing DSE/malloc/free optimization)

2011-09-08  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/19831
	* tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Do not mark
	allocation functions as necessary.

	* gcc.dg/tree-ssa/ssa-dce-8.c: New testcase.

From-SVN: r178683

gcc/ChangeLog

+2011-09-08  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/19831
+	* tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Do not mark
+	allocation functions as necessary.
+
 2011-09-08  Iain Sandoe  <iains@gcc.gnu.org>
 
 	*config/darwin-driver.c (darwin_find_version_from_kernel): New routine 

gcc/testsuite/ChangeLog

+2011-09-08  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/19831
+	* gcc.dg/tree-ssa/ssa-dce-8.c: New testcase.
+
 2011-09-08  Tobias Burnus  <burnus@net-b.de>
 
 	PR fortran/44646

gcc/testsuite/gcc.dg/tree-ssa/ssa-dce-8.c

+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-optimized" } */
+
+int main()
+{
+  int *p = __builtin_malloc (4);
+  *p = 4;
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump-not "malloc" "optimized" } } */
+/* { dg-final { cleanup-tree-dump "optimized" } } */

gcc/tree-ssa-dce.c

@@ -299,17 +299,29 @@ mark_stmt_if_obviously_necessary (gimple stmt, bool aggressive)
       return;
 
     case GIMPLE_CALL:
-      /* Most, but not all function calls are required.  Function calls that
-	 produce no result and have no side effects (i.e. const pure
-	 functions) are unnecessary.  */
-      if (gimple_has_side_effects (stmt))
-	{
-	  mark_stmt_necessary (stmt, true);
+      {
+	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_MALLOC:
+	    case BUILT_IN_CALLOC:
+	    case BUILT_IN_ALLOCA:
+	      return;
+	    }
+	/* Most, but not all function calls are required.  Function calls that
+	   produce no result and have no side effects (i.e. const pure
+	   functions) are unnecessary.  */
+	if (gimple_has_side_effects (stmt))
+	  {
+	    mark_stmt_necessary (stmt, true);
+	    return;
+	  }
+	if (!gimple_call_lhs (stmt))
 	  return;
-	}
-      if (!gimple_call_lhs (stmt))
-        return;
-      break;
+	break;
+      }
 
     case GIMPLE_DEBUG:
       /* Debug temps without a value are not useful.  ??? If we could