[PATCH] Fix ICE part of PR81546

[Richard Biener <rguenther at suse dot de>]

The following patch fixes the immediate use verifier error by
removing an artificial cap on the number of immediate uses (to
detect cycles).  We'd run into problems sooner or later in immediate
uses iteration anyways.

This allows the testcase to compile.  SLSR still goes crazy on this
testcase.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

2017-07-25  Richard Biener  <rguenther@suse.de>

	PR middle-end/81546
	* tree-ssa-operands.c (verify_imm_links): Remove cap on number
	of immediate uses, be more verbose on errors.

Index: gcc/tree-ssa-operands.c
===================================================================
--- gcc/tree-ssa-operands.c	(revision 250494)
+++ gcc/tree-ssa-operands.c	(working copy)
@@ -1139,7 +1139,7 @@ DEBUG_FUNCTION bool
 verify_imm_links (FILE *f, tree var)
 {
   use_operand_p ptr, prev, list;
-  int count;
+  unsigned int count;
 
   gcc_assert (TREE_CODE (var) == SSA_NAME);
 
@@ -1157,20 +1157,31 @@ verify_imm_links (FILE *f, tree var)
   for (ptr = list->next; ptr != list; )
     {
       if (prev != ptr->prev)
-	goto error;
+	{
+	  fprintf (f, "prev != ptr->prev\n");
+	  goto error;
+	}
 
       if (ptr->use == NULL)
-	goto error; /* 2 roots, or SAFE guard node.  */
+	{
+	  fprintf (f, "ptr->use == NULL\n");
+	  goto error; /* 2 roots, or SAFE guard node.  */
+	}
       else if (*(ptr->use) != var)
-	goto error;
+	{
+	  fprintf (f, "*(ptr->use) != var\n");
+	  goto error;
+	}
 
       prev = ptr;
       ptr = ptr->next;
 
-      /* Avoid infinite loops.  50,000,000 uses probably indicates a
-	 problem.  */
-      if (count++ > 50000000)
-	goto error;
+      count++;
+      if (count == 0)
+	{
+	  fprintf (f, "number of immediate uses doesn't fit unsigned int\n");
+	  goto error;
+	}
     }
 
   /* Verify list in the other direction.  */
@@ -1178,15 +1189,25 @@ verify_imm_links (FILE *f, tree var)
   for (ptr = list->prev; ptr != list; )
     {
       if (prev != ptr->next)
-	goto error;
+	{
+	  fprintf (f, "prev != ptr->next\n");
+	  goto error;
+	}
       prev = ptr;
       ptr = ptr->prev;
-      if (count-- < 0)
-	goto error;
+      if (count == 0)
+	{
+	  fprintf (f, "count-- < 0\n");
+	  goto error;
+	}
+      count--;
     }
 
   if (count != 0)
-    goto error;
+    {
+      fprintf (f, "count != 0\n");
+      goto error;
+    }
 
   return false;