[tuples] Avoid label_cont and jump to it if THEN sequence doesn't falltru

[Jakub Jelinek]

Hi!

This patch fixes
FAIL: g++.dg/warn/Wreturn-type-2.C (test for excess errors)
by omitting unnecessary goto which confuses fallthru detection.  The
difference is e.g.:

   if (x != y) goto <D.1> else goto <D.2>;
   <D.1>:
   ...
   return;
-  goto <D.3>;
   <D.2>:
   ...
   return;
-  <D.3>:

whenever the THEN sequence can't fallthru and the else sequence is
not empty (and isn't a simple goto which has been put already into
the GIMPLE_COND).
Bootstrapped/regtested on x86_64-linux, will commit momentarily.

2008-07-18  Jakub Jelinek  <jakub@redhat.com>

	* gimplify.c (gimplify_cond_expr): If COND_EXPR has both non-trivial
	THEN and ELSE statements and the THEN sequence can't fallthru, avoid
	adding label_cont and jump to it.

--- gcc/gimplify.c.jj	2008-07-17 18:10:18.000000000 +0200
+++ gcc/gimplify.c	2008-07-18 10:39:38.000000000 +0200
@@ -2988,9 +2988,12 @@ gimplify_cond_expr (tree *expr_p, gimple
 	  gimplify_seq_add_stmt (&seq, gimple_build_label (label_true));
 	  have_then_clause_p = gimplify_stmt (&TREE_OPERAND (expr, 1), &seq);
 	  /* For if (...) { code; } else {} or
-	     if (...) { code; } else goto label;
+	     if (...) { code; } else goto label; or
+	     if (...) { code; return; } else { ... }
 	     label_cont isn't needed.  */
-	  if (!have_else_clause_p && TREE_OPERAND (expr, 2) != NULL_TREE)
+	  if (!have_else_clause_p
+	      && TREE_OPERAND (expr, 2) != NULL_TREE
+	      && gimple_seq_may_fallthru (seq))
 	    {
 	      label_cont = create_artificial_label ();
 	      gimplify_seq_add_stmt (&seq, gimple_build_goto (label_cont));

	Jakub