Add unsigned type iv_cand for iv_use with non mode-precision type

Precisely,  for iv_use if it's not integer/pointer type, or non-mode
precision type, add candidate for the corresponding scev in unsigned
type with the same precision, rather than its original type.

gcc/
    PR tree-optimization/93674
    * tree-ssa-loop-ivopts.c (langhooks.h): New include.
    (add_iv_candidate_for_use): For iv_use of non integer or pointer type,
    or non-mode precision type, add candidate in unsigned type with the
    same precision.

gcc/testsuite/
    PR tree-optimization/93674
    * g++.dg/pr93674.C: New test.

gcc/ChangeLog

+2020-04-09  Bin Cheng  <bin.cheng@linux.alibaba.com>
+	    Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/93674
+	* tree-ssa-loop-ivopts.c (langhooks.h): New include.
+	(add_iv_candidate_for_use): For iv_use of non integer or pointer type,
+	or non-mode precision type, add candidate in unsigned type with the
+	same precision.
+
 2020-04-08  Clement Chigot  <clement.chigot@atos.net>
 
 	* config/rs6000/aix61.h (LIB_SPEC): Add -lc128 with -mlong-double-128.

gcc/testsuite/ChangeLog

+2020-04-09  Bin Cheng  <bin.cheng@linux.alibaba.com>
+
+	PR tree-optimization/93674
+	* g++.dg/pr93674.C: New test.
+
 2020-04-08  Sandra Loosemore  <sandra@codesourcery.com>
 
 	* g++.dg/tree-ssa/pr93940.C: Require pthread target.

gcc/testsuite/g++.dg/pr93674.C

+// { dg-do compile }
+// { dg-options "-O3 -std=c++14 -fstrict-enums -pedantic -fdump-tree-optimized" }
+enum some_enum { x = 1000 };
+void sink(some_enum);
+
+int __attribute__((noinline)) func() {
+  int sum = 0;
+  for (int i = 0; i < 3; ++i) {
+      for (int j = 3; j >= 0; --j) {
+          sink((some_enum)(i + j));
+      }
+  }
+  return sum;
+}
+
+// { dg-final { scan-tree-dump-not "some_enum ivtmp" "optimized" } }

gcc/tree-ssa-loop-ivopts.c

@@ -132,6 +132,9 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-vectorizer.h"
 #include "dbgcnt.h"
 
+/* For lang_hooks.types.type_for_mode.  */
+#include "langhooks.h"
+
 /* FIXME: Expressions are expanded to RTL in this pass to determine the
    cost of different addressing modes.  This should be moved to a TBD
    interface between the GIMPLE and RTL worlds.  */
@@ -3479,8 +3482,21 @@ add_iv_candidate_for_use (struct ivopts_data *data, struct iv_use *use)
 {
   poly_uint64 offset;
   tree base;
-  tree basetype;
   struct iv *iv = use->iv;
+  tree basetype = TREE_TYPE (iv->base);
+
+  /* Don't add candidate for iv_use with non integer, pointer or non-mode
+     precision types, instead, add candidate for the corresponding scev in
+     unsigned type with the same precision.  See PR93674 for more info.  */
+  if ((TREE_CODE (basetype) != INTEGER_TYPE && !POINTER_TYPE_P (basetype))
+      || !type_has_mode_precision_p (basetype))
+    {
+      basetype = lang_hooks.types.type_for_mode (TYPE_MODE (basetype),
+						 TYPE_UNSIGNED (basetype));
+      add_candidate (data, fold_convert (basetype, iv->base),
+		     fold_convert (basetype, iv->step), false, NULL);
+      return;
+    }
 
   add_candidate (data, iv->base, iv->step, false, use);