[patch, fortran] Put front-end temporaries into BLOCKs

[Thomas Koenig <tkoenig at netcologne dot de>]

Hello world,

the attached patch puts temporary variables, and the statement they are 
being generated for, in their own BLOCK.

This may or may not be useful for data locality, and for telling the 
middle end explicitly about the lifetime of the temporary variables.  It 
is intended as a step towards eliminating redundant calls to 
array-valued functions whose bounds are unknown at compile time, such as 
the original test case for PR 22572.

No test case, as this should not change anything.

Regression-tested.  OK for trunk?

	Thomas

2011-04-23  Thomas Koenig  <tkoenig@gcc.gnu.org>

        * frontend-passes.c (inserted_block):  New variable.
        (changed_statement):  Likewise.
        (create_var):  Encase statement to be operated on in a BLOCK.
        Adjust code insertion for BLOCK.
        (cfe_code):  Set inserted_block and changed_statement to NULL.

Index: frontend-passes.c
===================================================================
--- frontend-passes.c	(Revision 172856)
+++ frontend-passes.c	(Arbeitskopie)
@@ -48,10 +48,15 @@ static gfc_expr ***expr_array;
 static int expr_size, expr_count;
 
 /* Pointer to the gfc_code we currently work on - to be able to insert
-   a statement before.  */
+   a block before the statement.  */
 
 static gfc_code **current_code;
 
+/* Pointer to the block to be inserted, and the statement we are
+   changing within the block.  */
+
+static gfc_code *inserted_block, **changed_statement;
+
 /* The namespace we are currently dealing with.  */
 
 gfc_namespace *current_ns;
@@ -203,7 +208,9 @@ cfe_register_funcs (gfc_expr **e, int *walk_subtre
 
 /* Returns a new expression (a variable) to be used in place of the old one,
    with an an assignment statement before the current statement to set
-   the value of the variable.  */
+   the value of the variable. Creates a new BLOCK for the statement if
+   that hasn't already been done and puts the statement, plus the
+   newly created variables, in that block.  */
 
 static gfc_expr*
 create_var (gfc_expr * e)
@@ -214,10 +221,31 @@ create_var (gfc_expr * e)
   gfc_symbol *symbol;
   gfc_expr *result;
   gfc_code *n;
+  gfc_namespace *ns;
   int i;
 
+  /* If the block hasn't already been created, do so.  */
+  if (inserted_block == NULL)
+    {
+      inserted_block = XCNEW (gfc_code);
+      inserted_block->op = EXEC_BLOCK;
+      inserted_block->loc = (*current_code)->loc;
+      ns = gfc_build_block_ns (current_ns);
+      inserted_block->ext.block.ns = ns;
+      inserted_block->ext.block.assoc = NULL;
+
+      ns->code = *current_code;
+      inserted_block->next = (*current_code)->next;
+      changed_statement = &(inserted_block->ext.block.ns->code);
+      (*current_code)->next = NULL;
+      /* Insert the BLOCK at the right position.  */
+      *current_code = inserted_block;
+    }
+  else
+    ns = inserted_block->ext.block.ns;
+
   sprintf(name, "__var_%d",num++);
-  if (gfc_get_sym_tree (name, current_ns, &symtree, false) != 0)
+  if (gfc_get_sym_tree (name, ns, &symtree, false) != 0)
     gcc_unreachable ();
 
   symbol = symtree->n.sym;
@@ -267,10 +295,10 @@ create_var (gfc_expr * e)
   n = XCNEW (gfc_code);
   n->op = EXEC_ASSIGN;
   n->loc = (*current_code)->loc;
-  n->next = *current_code;
+  n->next = *changed_statement;
   n->expr1 = gfc_copy_expr (result);
   n->expr2 = e;
-  *current_code = n;
+  *changed_statement = n;
 
   return result;
 }
@@ -347,6 +375,8 @@ cfe_code (gfc_code **c, int *walk_subtrees ATTRIBU
 	  void *data ATTRIBUTE_UNUSED)
 {
   current_code = c;
+  inserted_block = NULL;
+  changed_statement = NULL;
   return 0;
 }