Re: Volatile MEMs in statement expressions and functions inlined as trees

[Alexandre Oliva <aoliva at redhat dot com>]

[switching back to non-private communication]

On Dec 31, 2001, Richard Henderson <rth@redhat.com> wrote:

>> http://gcc.gnu.org/ml/gcc-patches/2001-12/msg00542.html

> Ok.

Thanks.  I bootstrapped it again on athlon-pc-linux-gnu, now with Ada,
and tested it again, without regressions.  I'm yet to write some
testcases to avoid regressions and formalize the intended behavior,
but I'm not sure we've reached consensus yet, so I still haven't spend
the time to write it.

Here's the exact patch I'm checking in.  The only difference from the
previously-posted patch is the addition of 2002 in the copyright
notices.

Happy GNU Year! :-)

Index: gcc/ChangeLog
from  Alexandre Oliva  <aoliva@redhat.com>

	* c-common.h (genrtl_expr_stmt_value): Declare.
	* c-semantics.c (genrtl_goto_stmt): Redirect to...
	(genrtl_goto_stmt_value): ... this new function.  Pass new
	argument down to expand_expr_stmt_value, taking
	TREE_ADDRESSABLE into account.
	* c-common.c (c_expand_expr): Mark the last EXPR_STMT of a
	STMT_EXPR as addressable, i.e., one whose result we want.
	* expr.c (expand_expr): Don't save expression statement value
	of labeled_blocks or loop_exprs.
	* stmt.c (expand_expr_stmt): Redirect to...
	(expand_expr_stmt_value): ... this new function.  Use new
	argument to tell whether to save expression value.
	(expand_end_stmt_expr): Reset last_expr_type and
	last_expr_value if we don't have either.
	* tree-inline.c (declare_return_variable): Mark its use
	statement as addressable.
	* tree.h: Document new use of TREE_ADDRESSABLE.
	(expand_expr_stmt_value): Declare.

Index: gcc/c-common.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/c-common.c,v
retrieving revision 1.283
diff -u -p -r1.283 c-common.c
--- gcc/c-common.c 2001/12/21 02:36:35 1.283
+++ gcc/c-common.c 2002/01/02 02:20:37
@@ -1,6 +1,6 @@
 /* Subroutines shared by all languages that are variants of C.
-   Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001
-   Free Software Foundation, Inc.
+   Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
+   2001, 2002 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -3418,6 +3418,27 @@ c_expand_expr (exp, target, tmode, modif
 	   STMT_EXPR.  */
 	push_temp_slots ();
 	rtl_expr = expand_start_stmt_expr ();
+
+	/* If we want the result of this expression, find the last
+           EXPR_STMT in the COMPOUND_STMT and mark it as addressable.  */
+	if (target != const0_rtx
+	    && TREE_CODE (STMT_EXPR_STMT (exp)) == COMPOUND_STMT
+	    && TREE_CODE (COMPOUND_BODY (STMT_EXPR_STMT (exp))) == SCOPE_STMT)
+	  {
+	    tree expr = COMPOUND_BODY (STMT_EXPR_STMT (exp));
+	    tree last = TREE_CHAIN (expr);
+
+	    while (TREE_CHAIN (last))
+	      {
+		expr = last;
+		last = TREE_CHAIN (last);
+	      }
+
+	    if (TREE_CODE (last) == SCOPE_STMT
+		&& TREE_CODE (expr) == EXPR_STMT)
+	      TREE_ADDRESSABLE (expr) = 1;
+	  }
+
 	expand_stmt (STMT_EXPR_STMT (exp));
 	expand_end_stmt_expr (rtl_expr);
 	result = expand_expr (rtl_expr, target, tmode, modifier);
Index: gcc/c-common.h
===================================================================
RCS file: /cvs/gcc/egcs/gcc/c-common.h,v
retrieving revision 1.109
diff -u -p -r1.109 c-common.h
--- gcc/c-common.h 2001/12/17 01:18:38 1.109
+++ gcc/c-common.h 2002/01/02 02:20:38
@@ -1,6 +1,6 @@
 /* Definitions for c-common.c.
    Copyright (C) 1987, 1993, 1994, 1995, 1997, 1998,
-   1999, 2000, 2001 Free Software Foundation, Inc.
+   1999, 2000, 2001, 2002 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -717,6 +717,7 @@ extern void add_c_tree_codes		        PA
 extern void genrtl_do_pushlevel                 PARAMS ((void));
 extern void genrtl_goto_stmt                    PARAMS ((tree));
 extern void genrtl_expr_stmt                    PARAMS ((tree));
+extern void genrtl_expr_stmt_value              PARAMS ((tree, int));
 extern void genrtl_decl_stmt                    PARAMS ((tree));
 extern void genrtl_if_stmt                      PARAMS ((tree));
 extern void genrtl_while_stmt                   PARAMS ((tree));
Index: gcc/c-semantics.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/c-semantics.c,v
retrieving revision 1.34
diff -u -p -r1.34 c-semantics.c
--- gcc/c-semantics.c 2001/10/11 03:15:23 1.34
+++ gcc/c-semantics.c 2002/01/02 02:20:38
@@ -1,7 +1,7 @@
 /* This file contains the definitions and documentation for the common
    tree codes used in the GNU C and C++ compilers (see c-common.def
    for the standard codes).  
-   Copyright (C) 2000, 2001 Free Software Foundation, Inc.
+   Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc.
    Written by Benjamin Chelf (chelf@codesourcery.com).
 
 This file is part of GCC.
@@ -305,12 +305,27 @@ genrtl_goto_stmt (destination)
     expand_computed_goto (destination);
 }
 
-/* Generate the RTL for EXPR, which is an EXPR_STMT.  */
+/* Generate the RTL for EXPR, which is an EXPR_STMT.  Provided just
+   for backward compatibility.  genrtl_expr_stmt_value() should be
+   used for new code.  */
 
-void 
+void
 genrtl_expr_stmt (expr)
      tree expr;
 {
+  genrtl_expr_stmt_value (expr, -1);
+}
+
+/* Generate the RTL for EXPR, which is an EXPR_STMT.  WANT_VALUE tells
+   whether to (1) save the value of the expression, (0) discard it or
+   (-1) use expr_stmts_for_value to tell.  The use of -1 is
+   deprecated, and retained only for backward compatibility.  */
+
+void 
+genrtl_expr_stmt_value (expr, want_value)
+     tree expr;
+     int want_value;
+{
   if (expr != NULL_TREE)
     {
       emit_line_note (input_filename, lineno);
@@ -319,7 +334,7 @@ genrtl_expr_stmt (expr)
 	expand_start_target_temps ();
       
       if (expr != error_mark_node)
-	expand_expr_stmt (expr);
+	expand_expr_stmt_value (expr, want_value);
       
       if (stmts_are_full_exprs_p ())
 	expand_end_target_temps ();
@@ -748,7 +763,7 @@ expand_stmt (t)
 	  break;
 
 	case EXPR_STMT:
-	  genrtl_expr_stmt (EXPR_STMT_EXPR (t));
+	  genrtl_expr_stmt_value (EXPR_STMT_EXPR (t), TREE_ADDRESSABLE (t));
 	  break;
 
 	case DECL_STMT:
Index: gcc/expr.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/expr.c,v
retrieving revision 1.406
diff -u -p -r1.406 expr.c
--- gcc/expr.c 2001/12/29 21:35:01 1.406
+++ gcc/expr.c 2002/01/02 02:20:45
@@ -1,6 +1,6 @@
 /* Convert tree expression to rtl instructions, for GNU compiler.
    Copyright (C) 1988, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
-   2000, 2001 Free Software Foundation, Inc.
+   2000, 2001, 2002 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -6453,7 +6453,7 @@ expand_expr (exp, target, tmode, modifie
 
     case LABELED_BLOCK_EXPR:
       if (LABELED_BLOCK_BODY (exp))
-	expand_expr_stmt (LABELED_BLOCK_BODY (exp));
+	expand_expr_stmt_value (LABELED_BLOCK_BODY (exp), 0);
       /* Should perhaps use expand_label, but this is simpler and safer.  */
       do_pending_stack_adjust ();
       emit_label (label_rtx (LABELED_BLOCK_LABEL (exp)));
@@ -6468,7 +6468,7 @@ expand_expr (exp, target, tmode, modifie
     case LOOP_EXPR:
       push_temp_slots ();
       expand_start_loop (1);
-      expand_expr_stmt (TREE_OPERAND (exp, 0));
+      expand_expr_stmt_value (TREE_OPERAND (exp, 0), 0);
       expand_end_loop ();
       pop_temp_slots ();
 
Index: gcc/stmt.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/stmt.c,v
retrieving revision 1.240
diff -u -p -r1.240 stmt.c
--- gcc/stmt.c 2001/12/24 06:15:28 1.240
+++ gcc/stmt.c 2002/01/02 02:20:49
@@ -1,6 +1,6 @@
 /* Expands front end tree to back end RTL for GNU C-Compiler
    Copyright (C) 1987, 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997,
-   1998, 1999, 2000, 2001 Free Software Foundation, Inc.
+   1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -2182,16 +2182,37 @@ resolve_operand_name_1 (p, outputs, inpu
 }
 
 /* Generate RTL to evaluate the expression EXP
-   and remember it in case this is the VALUE in a ({... VALUE; }) constr.  */
+   and remember it in case this is the VALUE in a ({... VALUE; }) constr.
+   Provided just for backward-compatibility.  expand_expr_stmt_value()
+   should be used for new code.  */
 
 void
 expand_expr_stmt (exp)
      tree exp;
 {
+  expand_expr_stmt_value (exp, -1);
+}
+
+/* Generate RTL to evaluate the expression EXP.  WANT_VALUE tells
+   whether to (1) save the value of the expression, (0) discard it or
+   (-1) use expr_stmts_for_value to tell.  The use of -1 is
+   deprecated, and retained only for backward compatibility.  */
+
+void
+expand_expr_stmt_value (exp, want_value)
+     tree exp;
+     int want_value;
+{
+  rtx value;
+  tree type;
+
+  if (want_value == -1)
+    want_value = expr_stmts_for_value != 0;
+
   /* If -W, warn about statements with no side effects,
      except for an explicit cast to void (e.g. for assert()), and
      except inside a ({...}) where they may be useful.  */
-  if (expr_stmts_for_value == 0 && exp != error_mark_node)
+  if (! want_value && exp != error_mark_node)
     {
       if (! TREE_SIDE_EFFECTS (exp))
 	{
@@ -2207,34 +2228,31 @@ expand_expr_stmt (exp)
 
   /* If EXP is of function type and we are expanding statements for
      value, convert it to pointer-to-function.  */
-  if (expr_stmts_for_value && TREE_CODE (TREE_TYPE (exp)) == FUNCTION_TYPE)
+  if (want_value && TREE_CODE (TREE_TYPE (exp)) == FUNCTION_TYPE)
     exp = build1 (ADDR_EXPR, build_pointer_type (TREE_TYPE (exp)), exp);
 
   /* The call to `expand_expr' could cause last_expr_type and
      last_expr_value to get reset.  Therefore, we set last_expr_value
      and last_expr_type *after* calling expand_expr.  */
-  last_expr_value = expand_expr (exp,
-				 (expr_stmts_for_value
-				  ? NULL_RTX : const0_rtx),
-				 VOIDmode, 0);
-  last_expr_type = TREE_TYPE (exp);
+  value = expand_expr (exp, want_value ? NULL_RTX : const0_rtx,
+		       VOIDmode, 0);
+  type = TREE_TYPE (exp);
 
   /* If all we do is reference a volatile value in memory,
      copy it to a register to be sure it is actually touched.  */
-  if (last_expr_value != 0 && GET_CODE (last_expr_value) == MEM
-      && TREE_THIS_VOLATILE (exp))
+  if (value && GET_CODE (value) == MEM && TREE_THIS_VOLATILE (exp))
     {
-      if (TYPE_MODE (TREE_TYPE (exp)) == VOIDmode)
+      if (TYPE_MODE (type) == VOIDmode)
 	;
-      else if (TYPE_MODE (TREE_TYPE (exp)) != BLKmode)
-	copy_to_reg (last_expr_value);
+      else if (TYPE_MODE (type) != BLKmode)
+	value = copy_to_reg (value);
       else
 	{
 	  rtx lab = gen_label_rtx ();
 
 	  /* Compare the value with itself to reference it.  */
-	  emit_cmp_and_jump_insns (last_expr_value, last_expr_value, EQ,
-				   expand_expr (TYPE_SIZE (last_expr_type),
+	  emit_cmp_and_jump_insns (value, value, EQ,
+				   expand_expr (TYPE_SIZE (type),
 						NULL_RTX, VOIDmode, 0),
 				   BLKmode, 0, lab);
 	  emit_label (lab);
@@ -2243,13 +2261,19 @@ expand_expr_stmt (exp)
 
   /* If this expression is part of a ({...}) and is in memory, we may have
      to preserve temporaries.  */
-  preserve_temp_slots (last_expr_value);
+  preserve_temp_slots (value);
 
   /* Free any temporaries used to evaluate this expression.  Any temporary
      used as a result of this expression will already have been preserved
      above.  */
   free_temp_slots ();
 
+  if (want_value)
+    {
+      last_expr_value = value;
+      last_expr_type = type;
+    }
+
   emit_queue ();
 }
 
@@ -2386,6 +2410,7 @@ expand_start_stmt_expr ()
   start_sequence_for_rtl_expr (t);
   NO_DEFER_POP;
   expr_stmts_for_value++;
+  last_expr_value = NULL_RTX;
   return t;
 }
 
@@ -2407,15 +2432,11 @@ expand_end_stmt_expr (t)
 {
   OK_DEFER_POP;
 
-  if (last_expr_type == 0)
+  if (! last_expr_value || ! last_expr_type)
     {
-      last_expr_type = void_type_node;
       last_expr_value = const0_rtx;
+      last_expr_type = void_type_node;
     }
-  else if (last_expr_value == 0)
-    /* There are some cases where this can happen, such as when the
-       statement is void type.  */
-    last_expr_value = const0_rtx;
   else if (GET_CODE (last_expr_value) != REG && ! CONSTANT_P (last_expr_value))
     /* Remove any possible QUEUED.  */
     last_expr_value = protect_from_queue (last_expr_value, 0);
Index: gcc/tree-inline.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/tree-inline.c,v
retrieving revision 1.13
diff -u -p -r1.13 tree-inline.c
--- gcc/tree-inline.c 2001/12/06 17:58:23 1.13
+++ gcc/tree-inline.c 2002/01/02 02:20:50
@@ -1,5 +1,5 @@
 /* Control and data flow functions for trees.
-   Copyright 2001 Free Software Foundation, Inc.
+   Copyright 2001, 2002 Free Software Foundation, Inc.
    Contributed by Alexandre Oliva <aoliva@redhat.com>
 
 This file is part of GNU CC.
@@ -624,7 +624,9 @@ declare_return_variable (id, use_stmt)
     *use_stmt = build_stmt (EXPR_STMT,
 			    build1 (NOP_EXPR, TREE_TYPE (TREE_TYPE (fn)),
 				    var));
-      
+
+  TREE_ADDRESSABLE (*use_stmt) = 1;
+
   /* Build the declaration statement if FN does not return an
      aggregate.  */
   if (need_return_decl)
Index: gcc/tree.h
===================================================================
RCS file: /cvs/gcc/egcs/gcc/tree.h,v
retrieving revision 1.295
diff -u -p -r1.295 tree.h
--- gcc/tree.h 2001/12/31 04:07:11 1.295
+++ gcc/tree.h 2002/01/02 02:20:52
@@ -1,6 +1,6 @@
 /* Front-end tree definitions for GNU compiler.
-   Copyright (C) 1989, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001
-   Free Software Foundation, Inc.
+   Copyright (C) 1989, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
+   2001, 2002 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -161,7 +161,9 @@ struct tree_common
 
        TREE_ADDRESSABLE in
    	   VAR_DECL, FUNCTION_DECL, FIELD_DECL, CONSTRUCTOR, LABEL_DECL,
-	   ..._TYPE, IDENTIFIER_NODE
+	   ..._TYPE, IDENTIFIER_NODE.
+	   In a STMT_EXPR, it means we want the result of the enclosed
+	   expression.
 
    static_flag:
 
@@ -258,8 +260,7 @@ struct tree_common
 	   expressions, VAR_DECL, PARM_DECL, FIELD_DECL, FUNCTION_DECL,
 	   IDENTIFIER_NODE
        TYPE_BOUNDED in
-	   ..._TYPE
-*/
+	   ..._TYPE */
 
 /* Define accessors for the fields that all tree nodes have
    (though some fields are not used for all kinds of nodes).  */
@@ -2719,6 +2720,7 @@ extern void expand_fixups			PARAMS ((rtx
 extern tree expand_start_stmt_expr		PARAMS ((void));
 extern tree expand_end_stmt_expr		PARAMS ((tree));
 extern void expand_expr_stmt			PARAMS ((tree));
+extern void expand_expr_stmt_value		PARAMS ((tree, int));
 extern int warn_if_unused_value			PARAMS ((tree));
 extern void expand_decl_init			PARAMS ((tree));
 extern void clear_last_expr			PARAMS ((void));

-- 
Alexandre Oliva   Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer                  aoliva@{cygnus.com, redhat.com}
CS PhD student at IC-Unicamp        oliva@{lsd.ic.unicamp.br, gnu.org}
Free Software Evangelist    *Please* write to mailing lists, not to me