[PATCH PR43513, 1/3] Replace vla with array - Implementation.

[Tom de Vries <vries at codesourcery dot com>]

On 07/27/2011 01:50 PM, Tom de Vries wrote:
> Hi Richard,
> 
> I have a patch set for bug 43513 - The stack pointer is adjusted twice.
> 
> 01_pr43513.3.patch
> 02_pr43513.3.test.patch
> 03_pr43513.3.mudflap.patch
> 
> The patch set has been bootstrapped and reg-tested on x86_64.
> 
> I will sent out the patches individually.
> 

The patch replaces a vla __builtin_alloca that has a constant argument with an
array declaration.

OK for trunk?

Thanks,
- Tom

2011-07-27  Tom de Vries  <tom@codesourcery.com>

	PR middle-end/43513
	* builtins.c (fold_builtin_alloca): New function.
	* tree.h (fold_builtin_alloca): Declare.
	* gimple-fold.c (gimple_fold_builtin): Use fold_builtin_alloca.

Index: gcc/builtins.c
===================================================================
--- gcc/builtins.c	(revision 175801)
+++ gcc/builtins.c	(working copy)
@@ -6193,6 +6193,43 @@ builtin_mathfn_code (const_tree t)
   return DECL_FUNCTION_CODE (fndecl);
 }
 
+/* Detects a vla-related alloca with a constant argument.  Declares fixed-size
+   array and return the address, if found, otherwise returns NULL_TREE.  */
+
+tree
+fold_builtin_alloca (tree lhs, tree arg)
+{
+  unsigned HOST_WIDE_INT size, n_elem, elem_size;
+  tree var_type, vla_type, elem_type, array_type;
+
+  if (lhs == NULL_TREE)
+    return NULL_TREE;
+
+  /* Detect constant argument.  */
+  if (TREE_CODE (arg) != INTEGER_CST || !host_integerp (arg, 1))
+    return NULL_TREE;
+  size = TREE_INT_CST_LOW (arg);
+
+  /* Detect a vla.  */
+  var_type = TREE_TYPE (SSA_NAME_VAR (lhs));
+  if (TREE_CODE (var_type) != POINTER_TYPE)
+    return NULL_TREE;
+  vla_type = TREE_TYPE (var_type);
+  if (TREE_CODE (vla_type) != ARRAY_TYPE)
+    return NULL_TREE;
+  if (TREE_CODE (TYPE_MAXVAL (TYPE_DOMAIN (vla_type))) == INTEGER_CST)
+    return NULL_TREE;
+  elem_type = TREE_TYPE (vla_type);
+  if (TREE_CODE (TYPE_SIZE_UNIT (elem_type)) != INTEGER_CST)
+    return NULL_TREE;
+
+  /* Declare a fixed-size array and return the address instead.  */
+  elem_size = TREE_INT_CST_LOW (TYPE_SIZE_UNIT (elem_type));
+  n_elem = size / elem_size;
+  array_type = build_array_type_nelts (elem_type, n_elem);
+  return build_fold_addr_expr (create_tmp_var (array_type, "vla_cst"));
+}
+
 /* Fold a call to __builtin_constant_p, if we know its argument ARG will
    evaluate to a constant.  */
 
Index: gcc/tree.h
===================================================================
--- gcc/tree.h	(revision 175801)
+++ gcc/tree.h	(working copy)
@@ -5321,6 +5321,7 @@ truth_value_p (enum tree_code code)
 
 /* In builtins.c */
 extern tree fold_call_expr (location_t, tree, bool);
+extern tree fold_builtin_alloca (tree, tree);
 extern tree fold_builtin_fputs (location_t, tree, tree, bool, bool, tree);
 extern tree fold_builtin_strcpy (location_t, tree, tree, tree, tree);
 extern tree fold_builtin_strncpy (location_t, tree, tree, tree, tree, tree);
Index: gcc/gimple-fold.c
===================================================================
--- gcc/gimple-fold.c	(revision 175801)
+++ gcc/gimple-fold.c	(working copy)
@@ -1246,6 +1246,9 @@ gimple_fold_builtin (gimple stmt)
       arg_idx = 1;
       type = 2;
       break;
+    case BUILT_IN_ALLOCA:
+      return fold_builtin_alloca (gimple_call_lhs (stmt),
+				  gimple_call_arg (stmt, 0));
     default:
       return NULL_TREE;
     }