Fix ppc64le bootstrap comparison failure

[Jeff Law]

Given a block with more than one dead store, one of which is the last 
statement in the block, the existence debugging statements can change 
the generated code which is of course bad.

The problem is when I moved the code to delete the dead statement into 
its own function, I passed in the statement rather than the iterator. 
As a result  dse_dom_walker::before_dom_children would not see the 
iterator in the proper state and it would fail to walk all the 
statements if dse_optimize_stmt deleted the last statement in the block.

In a debug build that scenario was much less likely to trigger because 
of the existence of debug statements.

I'm installing this on the trunk now to fix the bootstrap issues.  I'll 
try to construct a testcase Monday.

Bootstrapped and regression tested on x86_64-linux-gnu and 
ppc64-linux-gnu.  Installing on the trunk.

Sorry for the breakage.

Jeff
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diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 3c74b19..d07b1f5 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,14 @@
+2017-01-13  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/33562
+	PR tree-optimization/61912
+	PR tree-optimization/77485
+	* tree-ssa-dse.c (delete_dead_call): Accept gsi rather than
+	a statement.
+	(delete_dead_assignment): Likewise.
+	(dse_dom_walker::dse_optimize_stmt): Pass in the gsi rather than
+	statement to delete_dead_call and delete_dead_assignment.
+
 2017-01-13  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c/78304
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index 20cf3b4..2e6f8ff 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -600,10 +600,11 @@ private:
   void dse_optimize_stmt (gimple_stmt_iterator *);
 };
 
-/* Delete a dead call STMT, which is mem* call of some kind.  */
+/* Delete a dead call at GSI, which is mem* call of some kind.  */
 static void
-delete_dead_call (gimple *stmt)
+delete_dead_call (gimple_stmt_iterator *gsi)
 {
+  gimple *stmt = gsi_stmt (*gsi);
   if (dump_file && (dump_flags & TDF_DETAILS))
     {
       fprintf (dump_file, "  Deleted dead call: ");
@@ -612,13 +613,12 @@ delete_dead_call (gimple *stmt)
     }
 
   tree lhs = gimple_call_lhs (stmt);
-  gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
   if (lhs)
     {
       tree ptr = gimple_call_arg (stmt, 0);
       gimple *new_stmt = gimple_build_assign (lhs, ptr);
       unlink_stmt_vdef (stmt);
-      if (gsi_replace (&gsi, new_stmt, true))
+      if (gsi_replace (gsi, new_stmt, true))
         bitmap_set_bit (need_eh_cleanup, gimple_bb (stmt)->index);
     }
   else
@@ -627,17 +627,18 @@ delete_dead_call (gimple *stmt)
       unlink_stmt_vdef (stmt);
 
       /* Remove the dead store.  */
-      if (gsi_remove (&gsi, true))
+      if (gsi_remove (gsi, true))
 	bitmap_set_bit (need_eh_cleanup, gimple_bb (stmt)->index);
       release_defs (stmt);
     }
 }
 
-/* Delete a dead store STMT, which is a gimple assignment. */
+/* Delete a dead store at GSI, which is a gimple assignment. */
 
 static void
-delete_dead_assignment (gimple *stmt)
+delete_dead_assignment (gimple_stmt_iterator *gsi)
 {
+  gimple *stmt = gsi_stmt (*gsi);
   if (dump_file && (dump_flags & TDF_DETAILS))
     {
       fprintf (dump_file, "  Deleted dead store: ");
@@ -649,9 +650,8 @@ delete_dead_assignment (gimple *stmt)
   unlink_stmt_vdef (stmt);
 
   /* Remove the dead store.  */
-  gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
   basic_block bb = gimple_bb (stmt);
-  if (gsi_remove (&gsi, true))
+  if (gsi_remove (gsi, true))
     bitmap_set_bit (need_eh_cleanup, bb->index);
 
   /* And release any SSA_NAMEs set in this statement back to the
@@ -717,7 +717,7 @@ dse_dom_walker::dse_optimize_stmt (gimple_stmt_iterator *gsi)
 		}
 
 	      if (store_status == DSE_STORE_DEAD)
-		delete_dead_call (stmt);
+		delete_dead_call (gsi);
 	      return;
 	    }
 
@@ -760,7 +760,7 @@ dse_dom_walker::dse_optimize_stmt (gimple_stmt_iterator *gsi)
 	  && !gimple_clobber_p (use_stmt))
 	return;
 
-      delete_dead_assignment (stmt);
+      delete_dead_assignment (gsi);
     }
 }