re PR tree-optimization/20640 (ICE on NULL PHI_ARG_DEF)

gcc/ChangeLog:
PR tree-optimization/20640
* tree-ssa-dce.c (remove_dead_stmt): Don't redirect edge to
post-dominator if it has phi nodes.
(eliminate_unnecessary_stmts): Remove dead phis in all blocks
before dead statements.
gcc/testsuite/ChangeLog:
PR tree-optimization/20640
* gcc.dg/torture/tree-loop-1.c: New.

From-SVN: r97446

gcc/ChangeLog

 2005-04-02  Alexandre Oliva  <aoliva@redhat.com>
 
+	PR tree-optimization/20640
+	* tree-ssa-dce.c (remove_dead_stmt): Don't redirect edge to
+	post-dominator if it has phi nodes.
+	(eliminate_unnecessary_stmts): Remove dead phis in all blocks
+	before dead statements.
+
+2005-04-02  Alexandre Oliva  <aoliva@redhat.com>
+
 	PR middle-end/20491
 	* final.c (alter_subreg): Don't call subreg_regno for a non-REG.
 

gcc/testsuite/ChangeLog

 2005-04-02  Alexandre Oliva  <aoliva@redhat.com>
 
+	PR tree-optimization/20640
+	* gcc.dg/torture/tree-loop-1.c: New.
+
+2005-04-02  Alexandre Oliva  <aoliva@redhat.com>
+
 	PR rtl-optimization/20290
 	* gcc.c-torture/execute/loop-ivopts-2.c: New.
 

gcc/testsuite/gcc.dg/torture/tree-loop-1.c

+/* PR tree-optimization/20640 */
+
+/* After unrolling the loop, we'd turn some conditional branches into
+   unconditional ones, but branch redirection would fail to compute
+   the PHI args for the PHI nodes in the replacement edge
+   destination, so they'd remain NULL causing crashes later on.  */
+
+/* { dg-do compile } */
+
+static int a = 0;
+extern int foo (void);
+extern int *bar (void) __attribute__ ((__const__));
+
+void
+test (int x)
+{
+  int b = 10;
+  while (foo () == -1 && *bar () == 4 && b > 0)
+    --b;
+  a = x;
+}

gcc/tree-ssa-dce.c

@@ -637,7 +637,10 @@ eliminate_unnecessary_stmts (void)
     {
       /* Remove dead PHI nodes.  */
       remove_dead_phis (bb);
+    }
 
+  FOR_EACH_BB (bb)
+    {
       /* Remove dead statements.  */
       for (i = bsi_start (bb); ! bsi_end_p (i) ; )
 	{
@@ -724,6 +727,7 @@ remove_dead_stmt (block_stmt_iterator *i, basic_block bb)
   if (is_ctrl_stmt (t))
     {
       basic_block post_dom_bb;
+
       /* The post dominance info has to be up-to-date.  */
       gcc_assert (dom_computed[CDI_POST_DOMINATORS] == DOM_OK);
       /* Get the immediate post dominator of bb.  */
@@ -737,9 +741,20 @@ remove_dead_stmt (block_stmt_iterator *i, basic_block bb)
 	  return;
 	}
 
-      /* Redirect the first edge out of BB to reach POST_DOM_BB.  */
-      redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb);
-      PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL;
+      /* If the post dominator block has PHI nodes, we might be unable
+	 to compute the right PHI args for them.  Since the control
+	 statement is unnecessary, all edges can be regarded as
+	 equivalent, but we have to get rid of the condition, since it
+	 might reference a variable that was determined to be
+	 unnecessary and thus removed.  */
+      if (phi_nodes (post_dom_bb))
+	post_dom_bb = EDGE_SUCC (bb, 0)->dest;
+      else
+	{
+	  /* Redirect the first edge out of BB to reach POST_DOM_BB.  */
+	  redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb);
+	  PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL;
+	}
       EDGE_SUCC (bb, 0)->probability = REG_BR_PROB_BASE;
       EDGE_SUCC (bb, 0)->count = bb->count;