common.opt (fkeep-gc-roots-live): New undocumented option.

gcc/:
	* common.opt (fkeep-gc-roots-live): New undocumented option.
	* tree-ssa-loop-ivopts.c (add_candidate_1): If
	-fkeep-gc-roots-live, skip pointers.
	(add_iv_candidate_for_biv): Handle add_candidate_1 returning
	NULL.

gcc/testsuite/:
	* gcc.dg/tree-ssa/ivopt_5.c: New test.

From-SVN: r232888

gcc/ChangeLog

@@ -1,3 +1,11 @@
+2016-01-27  Ian Lance Taylor  <iant@google.com>
+
+	* common.opt (fkeep-gc-roots-live): New undocumented option.
+	* tree-ssa-loop-ivopts.c (add_candidate_1): If
+	-fkeep-gc-roots-live, skip pointers.
+	(add_iv_candidate_for_biv): Handle add_candidate_1 returning
+	NULL.
+
 2016-01-27  Uros Bizjak  <ubizjak@gmail.com>
 
 	PR target/69512

gcc/common.opt

@@ -1380,6 +1380,10 @@ Common Report Var(flag_hoist_adjacent_loads) Optimization
 Enable hoisting adjacent loads to encourage generating conditional move
 instructions.
 
+fkeep-gc-roots-live
+Common Undocumented Report Var(flag_keep_gc_roots_live) Optimization
+; Always keep a pointer to a live memory block
+
 floop-parallelize-all
 Common Report Var(flag_loop_parallelize_all) Optimization
 Mark all loops as parallel.

gcc/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2016-01-27  Ian Lance Taylor  <iant@google.com>
+
+	* gcc.dg/tree-ssa/ivopt_5.c: New test.
+
 2016-01-27  Ryan Burn  <contact@rnburn.com>
 
 	PR cilkplus/69267

gcc/testsuite/gcc.dg/tree-ssa/ivopt_5.c

@@ -0,0 +1,23 @@
+/* { dg-options "-O2 -fdump-tree-ivopts -fkeep-gc-roots-live" } */
+
+/* Only integer ivopts here when using -fkeep-gc-roots-live.   */
+
+void foo (char *pstart, int n)
+{
+  char *p;
+  char *pend = pstart + n;
+
+  for (p = pstart; p < pend; p++)
+    *p = 1;
+}
+
+void foo1 (char *pstart, int n)
+{
+  char *p;
+  char *pend = pstart + n;
+
+  for (p = pstart; p != pend; p++)
+    *p = 1;
+}
+
+/* { dg-final { scan-tree-dump-times "ivtmp.\[0-9_\]* = PHI <\[^0\]" 0 "ivopts"} } */

gcc/tree-ssa-loop-ivopts.c

@@ -2815,6 +2815,16 @@ add_candidate_1 (struct ivopts_data *data,
   struct iv_cand *cand = NULL;
   tree type, orig_type;
 
+  /* -fkeep-gc-roots-live means that we have to keep a real pointer
+     live, but the ivopts code may replace a real pointer with one
+     pointing before or after the memory block that is then adjusted
+     into the memory block during the loop.  FIXME: It would likely be
+     better to actually force the pointer live and still use ivopts;
+     for example, it would be enough to write the pointer into memory
+     and keep it there until after the loop.  */
+  if (flag_keep_gc_roots_live && POINTER_TYPE_P (TREE_TYPE (base)))
+    return NULL;
+
   /* For non-original variables, make sure their values are computed in a type
      that does not invoke undefined behavior on overflows (since in general,
      we cannot prove that these induction variables are non-wrapping).  */
@@ -3083,8 +3093,11 @@ add_iv_candidate_for_biv (struct ivopts_data *data, struct iv *iv)
 	  cand = add_candidate_1 (data,
 				  iv->base, iv->step, true, IP_ORIGINAL, NULL,
 				  SSA_NAME_DEF_STMT (def));
-	  cand->var_before = iv->ssa_name;
-	  cand->var_after = def;
+	  if (cand)
+	    {
+	      cand->var_before = iv->ssa_name;
+	      cand->var_after = def;
+	    }
 	}
       else
 	gcc_assert (gimple_bb (phi) == data->current_loop->header);