tree.c (lang_safe_for_unsave): Remove.

        * tree.c (lang_safe_for_unsave): Remove.
        (unsafe_for_reeval): Transmute and rename from safe_for_unsave,
        allowing for two levels of unsafeness.  Remove lang hook.
        * tree.h: Update declarations.
        * calls.c (expand_call): Rename safe_for_reeval to try_tail_call.
        Create temporary VAR_DECLs to protect very unsafe_for_reeval trees.
        Always fail sibcalls when there are pending cleanups.

From-SVN: r32735

4 files changed, 112 insertions, 61 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index dfd53dd..8ca4e95 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,13 @@
+2000-03-24  Richard Henderson  <rth@cygnus.com>
+
+	* tree.c (lang_safe_for_unsave): Remove.
+	(unsafe_for_reeval): Transmute and rename from safe_for_unsave,
+	allowing for two levels of unsafeness.  Remove lang hook.
+	* tree.h: Update declarations.
+	* calls.c (expand_call): Rename safe_for_reeval to try_tail_call.
+	Create temporary VAR_DECLs to protect very unsafe_for_reeval trees.
+	Always fail sibcalls when there are pending cleanups.
+
 2000-03-24  Geoff Keating  <geoffk@cygnus.com>
 
 	* flow.c (propagate_block): When we delete an ADDR_VEC,
diff --git a/gcc/calls.c b/gcc/calls.c
index 0a8688c..ed4b31b 100644
--- a/gcc/calls.c
+++ b/gcc/calls.c
@@ -1696,7 +1696,7 @@ expand_call (exp, target, ignore)
   rtx before_call;
 #endif
   rtx insn;
-  int safe_for_reeval;
+  int try_tail_call;
   int pass;
 
   /* Register in which non-BLKmode value will be returned,
@@ -2027,44 +2027,70 @@ expand_call (exp, target, ignore)
 
   currently_expanding_call++;
 
-  /* If we're considering tail recursion optimizations, verify that the
-     arguments are safe for re-evaluation.  If we can unsave them, wrap
-     each argument in an UNSAVE_EXPR.  */
+  /* Tail calls can make things harder to debug, and we're traditionally
+     pushed these optimizations into -O2.  Don't try if we're already
+     expanding a call, as that means we're an argument.  Similarly, if
+     there's pending loops or cleanups we know there's code to follow
+     the call.  */
 
-  safe_for_reeval = 0;
+  try_tail_call = 0;
   if (optimize >= 2
       && currently_expanding_call == 1
       && stmt_loop_nest_empty ()
       && ! any_pending_cleanups (1))
     {
-      /* Verify that each argument is safe for re-evaluation.  */
+      tree new_actparms = NULL_TREE;
+
+      /* Ok, we're going to give the tail call the old college try.
+	 This means we're going to evaluate the function arguments
+	 up to three times.  There are two degrees of badness we can
+	 encounter, those that can be unsaved and those that can't.
+	 (See unsafe_for_reeval commentary for details.)
+
+	 Generate a new argument list.  Pass safe arguments through
+	 unchanged.  For the easy badness wrap them in UNSAVE_EXPRs.  
+	 For hard badness, evaluate them now and put their resulting
+	 rtx in a temporary VAR_DECL.  */
+
       for (p = actparms; p; p = TREE_CHAIN (p))
-	if (! safe_for_unsave (TREE_VALUE (p)))
-	  break;
+	switch (unsafe_for_reeval (TREE_VALUE (p)))
+	  {
+	  case 0: /* Safe.  */
+	    new_actparms = tree_cons (TREE_PURPOSE (p), TREE_VALUE (p),
+				      new_actparms);
+	    break;
 
-      if (p == NULL_TREE)
-        {
-	  tree new_actparms = NULL_TREE, q;
+	  case 1: /* Mildly unsafe.  */
+	    new_actparms = tree_cons (TREE_PURPOSE (p),
+				      unsave_expr (TREE_VALUE (p)),
+				      new_actparms);
+	    break;
 
-	  for (p = actparms; p ; p = TREE_CHAIN (p))
+	  case 2: /* Wildly unsafe.  */
 	    {
-	      tree np = build_tree_list (TREE_PURPOSE (p),
-					 unsave_expr (TREE_VALUE (p)));
-	      if (new_actparms)
-		TREE_CHAIN (q) = np;
-	      else
-		new_actparms = np;
-	      q = np;
+	      tree var = build_decl (VAR_DECL, NULL_TREE,
+				     TREE_TYPE (TREE_VALUE (p)));
+	      DECL_RTL (var) = expand_expr (TREE_VALUE (p), NULL_RTX,
+					    VOIDmode, EXPAND_NORMAL);
+	      new_actparms = tree_cons (TREE_PURPOSE (p), var, new_actparms);
 	    }
+	    break;
 
-	  actparms = new_actparms;
-	  safe_for_reeval = 1;
-	}
+	  default:
+	    abort ();
+	  }
+
+      /* We built the new argument chain backwards.  */
+      actparms = nreverse (new_actparms);
+
+      /* Expanding one of those dangerous arguments could have added
+	 cleanups, but otherwise give it a whirl.  */
+      try_tail_call = ! any_pending_cleanups (1);
     }
 
   /* Generate a tail recursion sequence when calling ourselves.  */
 
-  if (safe_for_reeval
+  if (try_tail_call
       && TREE_CODE (TREE_OPERAND (exp, 0)) == ADDR_EXPR
       && TREE_OPERAND (TREE_OPERAND (exp, 0), 0) == current_function_decl)
     {
@@ -2149,7 +2175,7 @@ expand_call (exp, target, ignore)
       if (pass == 0)
 	{
 	  /* Various reasons we can not use a sibling call.  */
-	  if (! safe_for_reeval
+	  if (! try_tail_call 
 #ifdef HAVE_sibcall_epilogue
 	      || ! HAVE_sibcall_epilogue
 #else
@@ -2163,6 +2189,10 @@ expand_call (exp, target, ignore)
 	      /* If the register holding the address is a callee saved
 		 register, then we lose.  We have no way to prevent that,
 		 so we only allow calls to named functions.  */
+	      /* ??? This could be done by having the insn constraints
+		 use a register class that is all call-clobbered.  Any
+		 reload insns generated to fix things up would appear
+		 before the sibcall_epilogue.  */
 	      || fndecl == NULL_TREE
 	      || ! FUNCTION_OK_FOR_SIBCALL (fndecl))
 	    continue;
@@ -2819,10 +2849,13 @@ expand_call (exp, target, ignore)
 
       /* If there are cleanups to be called, don't use a hard reg as target.
 	 We need to double check this and see if it matters anymore.  */
-      if (any_pending_cleanups (1)
-	  && target && REG_P (target)
-	  && REGNO (target) < FIRST_PSEUDO_REGISTER)
-	target = 0, sibcall_failure = 1;
+      if (any_pending_cleanups (1))
+	{
+	  if (target && REG_P (target)
+	      && REGNO (target) < FIRST_PSEUDO_REGISTER)
+	    target = 0;
+	  sibcall_failure = 1;
+	}
 
       if (TYPE_MODE (TREE_TYPE (exp)) == VOIDmode
 	  || ignore)
diff --git a/gcc/tree.c b/gcc/tree.c
index 3063dc6..51c8c38 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -290,9 +290,6 @@ static void print_type_hash_statistics PARAMS((void));
 void (*lang_unsave) PARAMS ((tree *));
 void (*lang_unsave_expr_now) PARAMS ((tree));
 
-/* If non-null, a language specific version of safe_for_unsave. */
-int (*lang_safe_for_unsave) PARAMS ((tree));
-
 /* The string used as a placeholder instead of a source file name for
    built-in tree nodes.  The variable, which is dynamically allocated,
    should be used; the macro is only used to initialize it.  */
@@ -2675,15 +2672,28 @@ unsave_expr_now (expr)
   return expr;
 }
 
-/* Return nonzero if it is safe to unsave EXPR, else return zero.
-   It is not safe to unsave EXPR if it contains any embedded RTL_EXPRs.  */
+/* Return 0 if it is safe to evaluate EXPR multiple times,
+   return 1 if it is safe if EXPR is unsaved afterward, or
+   return 2 if it is completely unsafe. 
+
+   This assumes that CALL_EXPRs and TARGET_EXPRs are never replicated in
+   an expression tree, so that it safe to unsave them and the surrounding
+   context will be correct.
+
+   SAVE_EXPRs basically *only* appear replicated in an expression tree,
+   occasionally across the whole of a function.  It is therefore only
+   safe to unsave a SAVE_EXPR if you know that all occurrences appear
+   below the UNSAVE_EXPR.
+
+   RTL_EXPRs consume their rtl during evaluation.  It is therefore 
+   never possible to unsave them.  */
 
 int
-safe_for_unsave (expr)
+unsafe_for_reeval (expr)
      tree expr;
 {
   enum tree_code code;
-  register int i;
+  register int i, tmp, unsafeness;
   int first_rtl;
 
   if (expr == NULL_TREE)
@@ -2691,10 +2701,13 @@ safe_for_unsave (expr)
 
   code = TREE_CODE (expr);
   first_rtl = first_rtl_op (code);
+  unsafeness = 0;
+
   switch (code)
     {
+    case SAVE_EXPR:
     case RTL_EXPR:
-      return 0;
+      return 2;
 
     case CALL_EXPR:
       if (TREE_OPERAND (expr, 1)
@@ -2703,26 +2716,20 @@ safe_for_unsave (expr)
 	  tree exp = TREE_OPERAND (expr, 1);
 	  while (exp)
 	    {
-	      if (! safe_for_unsave (TREE_VALUE (exp)))
-		return 0;
+	      tmp = unsafe_for_reeval (TREE_VALUE (exp));
+	      if (tmp > 1)
+		return tmp;
 	      exp = TREE_CHAIN (exp);
 	    }
 	}
+      return 1;
+
+    case TARGET_EXPR:
+      unsafeness = 1;
       break;
 
     default:
-      if (lang_safe_for_unsave)
-	switch ((*lang_safe_for_unsave) (expr))
-	  {
-	  case -1:
-	    break;
-	  case 0:
-	    return 0;
-	  case 1:
-	    return 1;
-	  default:
-	    abort ();
-	  }
+      /* ??? Add a lang hook if it becomes necessary.  */
       break;
     }
 
@@ -2733,7 +2740,7 @@ safe_for_unsave (expr)
     case 'x':  /* something random, like an identifier or an ERROR_MARK.  */
     case 'd':  /* A decl node */
     case 'b':  /* A block node */
-      return 1;
+      return 0;
 
     case 'e':  /* an expression */
     case 'r':  /* a reference */
@@ -2742,12 +2749,15 @@ safe_for_unsave (expr)
     case '2':  /* a binary arithmetic expression */
     case '1':  /* a unary arithmetic expression */
       for (i = first_rtl - 1; i >= 0; i--)
-	if (! safe_for_unsave (TREE_OPERAND (expr, i)))
-	  return 0;
-      return 1;
+	{
+	  tmp = unsafe_for_reeval (TREE_OPERAND (expr, i));
+	  if (tmp > unsafeness)
+	    unsafeness = tmp;
+	}
+      return unsafeness;
 
     default:
-      return 0;
+      return 2;
     }
 }
 
diff --git a/gcc/tree.h b/gcc/tree.h
index 61e7818..bc5225c 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -1963,12 +1963,10 @@ extern tree unsave_expr_now		PARAMS ((tree));
 extern void (*lang_unsave)              PARAMS ((tree *));
 extern void (*lang_unsave_expr_now)     PARAMS ((tree));
 
-/* If non-null, a language specific version of safe_for_unsave. */
-extern int (*lang_safe_for_unsave)	PARAMS ((tree));
-
-/* Return nonzero if it is safe to unsave EXPR, else return zero.
-   It is not safe to unsave EXPR if it contains any embedded RTL_EXPRs.  */
-extern int safe_for_unsave PARAMS ((tree));
+/* Return 0 if it is safe to evaluate EXPR multiple times,
+   return 1 if it is safe if EXPR is unsaved afterward, or
+   return 2 if it is completely unsafe.  */
+extern int unsafe_for_reeval PARAMS ((tree));
 
 /* Return 1 if EXP contains a PLACEHOLDER_EXPR; i.e., if it represents a size
    or offset that depends on a field within a record.