PATCH RFA: C frontend: Generate SWITCH_EXPR rather than SWITCH_STMT

[Ian Lance Taylor <ian at airs dot com>]

This patch changes the C frontend to generate SWITCH_EXPR rather than
SWITCH_STMT.  SWITCH_EXPR is GENERIC, unlike SWITCH_STMT which is
specific to the C/C++ frontends.  Generating SWITCH_EXPR directly
saves a call to gimplify_switch_stmt for each switch statement.

The real point of this patch is that, once it is accepted, it should
be straightforward to move the various loop constructs out of the
C/C++ common code into the C++ frontend.  The C frontend no longer
generates FOR_STMT, WHILE_STMT, etc.  Having it no longer generate
SWITCH_STMT makes it a little easier to move these all into the C++
frontend, as SWITCH_STMT is the last tree generated by the C frontend
which (when used by the C++ frontend) requires handling of BREAK_STMT
and CONTINUE_STMT.

It would also be possible to change the C++ frontend to no longer
generate these looping constructs, but to emit GENERIC directly.
However, my present understanding is that the C++ frontend maintainers
would prefer to continue to generate them.  This is evidently not the
case for the C frontend, which stopped generating them via a patch by
RTH last June.

Tested using a bootstrap and testsuite run on i686-pc-linux-gnu.  OK
for mainline?

Ian


2005-04-03  Ian Lance Taylor  <ian@airs.com>

	* c-typeck.c (struct c_switch): Rename switch_stmt field to
	switch_expr.
	(c_start_case): Build SWITCH_EXPR, not SWITCH_STMT.
	(do_case): Use SWITCH_COND rather than SWITCH_STMT_COND.
	(c_finish_case): Use SWITCH_BODY rather than SWITCH_STMT_BODY.
	Call c_do_switch_expr_warnings rather than c_do_switch_warnings.
	* c-common.c (c_do_switch_warnings_1): New static function broken
	out of c_do_switch_warnings.
	(c_do_switch_warnings): Call c_do_switch_warnings_1.
	(c_do_switch_expr_warnings): New function.
	* c-common.h (c_do_switch_expr_warnings): Declare.


Index: c-common.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-common.c,v
retrieving revision 1.618
diff -p -u -r1.618 c-common.c
--- c-common.c	30 Mar 2005 01:35:01 -0000	1.618
+++ c-common.c	3 Apr 2005 14:42:19 -0000
@@ -3708,32 +3708,17 @@ match_case_to_enum (splay_tree_node node
   return 0;
 }
 
-/* Handle -Wswitch*.  Called from the front end after parsing the switch
-   construct.  */
-/* ??? Should probably be somewhere generic, since other languages besides
-   C and C++ would want this.  We'd want to agree on the data structure,
-   however, which is a problem.  Alternately, we operate on gimplified
-   switch_exprs, which I don't especially like.  At the moment, however,
-   C/C++ are the only tree-ssa languages that support enumerations at all,
-   so the point is moot.  */
+/* Common code for -Wswitch*.  */
 
-void
-c_do_switch_warnings (splay_tree cases, tree switch_stmt)
+static void
+c_do_switch_warnings_1 (splay_tree cases, location_t switch_location,
+			tree type, tree cond)
 {
   splay_tree_node default_node;
-  location_t switch_location;
-  tree type;
 
   if (!warn_switch && !warn_switch_enum && !warn_switch_default)
     return;
 
-  if (EXPR_HAS_LOCATION (switch_stmt))
-    switch_location = EXPR_LOCATION (switch_stmt);
-  else
-    switch_location = input_location;
-
-  type = SWITCH_STMT_TYPE (switch_stmt);
-
   default_node = splay_tree_lookup (cases, (splay_tree_key) NULL);
   if (warn_switch_default && !default_node)
     warning ("%Hswitch missing default case", &switch_location);
@@ -3744,7 +3729,7 @@ c_do_switch_warnings (splay_tree cases, 
      default case, or when -Wswitch-enum was specified.  */
   if (((warn_switch && !default_node) || warn_switch_enum)
       && type && TREE_CODE (type) == ENUMERAL_TYPE
-      && TREE_CODE (SWITCH_STMT_COND (switch_stmt)) != INTEGER_CST)
+      && TREE_CODE (cond) != INTEGER_CST)
     {
       tree chain;
 
@@ -3788,6 +3773,45 @@ c_do_switch_warnings (splay_tree cases, 
     }
 }
 
+/* Handle -Wswitch* for a SWITCH_STMT.  Called from the front end
+   after parsing the switch construct.  */
+/* ??? Should probably be somewhere generic, since other languages besides
+   C and C++ would want this.  We'd want to agree on the data structure,
+   however, which is a problem.  Alternately, we operate on gimplified
+   switch_exprs, which I don't especially like.  At the moment, however,
+   C/C++ are the only tree-ssa languages that support enumerations at all,
+   so the point is moot.  */
+
+void
+c_do_switch_warnings (splay_tree cases, tree switch_stmt)
+{
+  location_t switch_location;
+
+  if (EXPR_HAS_LOCATION (switch_stmt))
+    switch_location = EXPR_LOCATION (switch_stmt);
+  else
+    switch_location = input_location;
+  c_do_switch_warnings_1 (cases, switch_location,
+			  SWITCH_STMT_TYPE (switch_stmt),
+			  SWITCH_STMT_COND (switch_stmt));
+}
+
+/* Like c_do_switch_warnings, but takes a SWITCH_EXPR rather than a
+   SWITCH_STMT.  */
+
+void
+c_do_switch_expr_warnings (splay_tree cases, tree switch_expr)
+{
+  location_t switch_location;
+
+  if (EXPR_HAS_LOCATION (switch_expr))
+    switch_location = EXPR_LOCATION (switch_expr);
+  else
+    switch_location = input_location;
+  c_do_switch_warnings_1 (cases, switch_location, TREE_TYPE (switch_expr),
+			  SWITCH_COND (switch_expr));
+}
+
 /* Finish an expression taking the address of LABEL (an
    IDENTIFIER_NODE).  Returns an expression for the address.  */
 
Index: c-common.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-common.h,v
retrieving revision 1.280
diff -p -u -r1.280 c-common.h
--- c-common.h	30 Mar 2005 01:35:02 -0000	1.280
+++ c-common.h	3 Apr 2005 14:42:19 -0000
@@ -825,6 +825,7 @@ extern int case_compare (splay_tree_key,
 extern tree c_add_case_label (splay_tree, tree, tree, tree, tree);
 
 extern void c_do_switch_warnings (splay_tree, tree);
+extern void c_do_switch_expr_warnings (splay_tree, tree);
 
 extern tree build_function_call (tree, tree);
 
Index: c-typeck.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/c-typeck.c,v
retrieving revision 1.429
diff -p -u -r1.429 c-typeck.c
--- c-typeck.c	30 Mar 2005 19:56:30 -0000	1.429
+++ c-typeck.c	3 Apr 2005 14:42:20 -0000
@@ -6609,8 +6609,8 @@ c_finish_return (tree retval)
 }
 
 struct c_switch {
-  /* The SWITCH_STMT being built.  */
-  tree switch_stmt;
+  /* The SWITCH_EXPR being built.  */
+  tree switch_expr;
 
   /* The original type of the testing expression, i.e. before the
      default conversion is applied.  */
@@ -6641,7 +6641,7 @@ struct c_switch {
 struct c_switch *c_switch_stack;
 
 /* Start a C switch statement, testing expression EXP.  Return the new
-   SWITCH_STMT.  */
+   SWITCH_EXPR.  */
 
 tree
 c_start_case (tree exp)
@@ -6677,16 +6677,16 @@ c_start_case (tree exp)
 	}
     }
 
-  /* Add this new SWITCH_STMT to the stack.  */
+  /* Add this new SWITCH_EXPR to the stack.  */
   cs = XNEW (struct c_switch);
-  cs->switch_stmt = build_stmt (SWITCH_STMT, exp, NULL_TREE, orig_type);
+  cs->switch_expr = build3 (SWITCH_EXPR, orig_type, exp, NULL_TREE, NULL_TREE);
   cs->orig_type = orig_type;
   cs->cases = splay_tree_new (case_compare, NULL, NULL);
   cs->blocked_stmt_expr = 0;
   cs->next = c_switch_stack;
   c_switch_stack = cs;
 
-  return add_stmt (cs->switch_stmt);
+  return add_stmt (cs->switch_expr);
 }
 
 /* Process a case label.  */
@@ -6699,7 +6699,7 @@ do_case (tree low_value, tree high_value
   if (c_switch_stack && !c_switch_stack->blocked_stmt_expr)
     {
       label = c_add_case_label (c_switch_stack->cases,
-				SWITCH_STMT_COND (c_switch_stack->switch_stmt),
+				SWITCH_COND (c_switch_stack->switch_expr),
 				c_switch_stack->orig_type,
 				low_value, high_value);
       if (label == error_mark_node)
@@ -6729,12 +6729,12 @@ c_finish_case (tree body)
 {
   struct c_switch *cs = c_switch_stack;
 
-  SWITCH_STMT_BODY (cs->switch_stmt) = body;
+  SWITCH_BODY (cs->switch_expr) = body;
 
   gcc_assert (!cs->blocked_stmt_expr);
 
   /* Emit warnings as needed.  */
-  c_do_switch_warnings (cs->cases, cs->switch_stmt);
+  c_do_switch_expr_warnings (cs->cases, cs->switch_expr);
 
   /* Pop the stack.  */
   c_switch_stack = cs->next;