Re: [PATCH] Fix up go regressions caused by my recent switchconv changes (PR go/91617)

[Jakub Jelinek <jakub@redhat.com>]

On Sat, Aug 31, 2019 at 07:23:35PM +0200, Richard Biener wrote:
> Hmm, couldn't we make range_check_type_for take an argument whether signed
> or unsigned type is required?  That is, what do we do if the caller wants
> a signed type?  Leaving it unspecified what the function returns is odd.

I think we never want specially signed type, either we don't care whether it
is signed or not, in that case we want just some type that wraps around, or we
do want an unsigned type.

So something like below, with using range_check_type (x, true) in some
places.

Note it will be more compile time expensive than just calling
unsigned_type_for after the range_check_type call, due to all the
wrap-around verification it does.

--- gcc/fold-const.h.jj	2019-08-08 08:34:28.010306157 +0200
+++ gcc/fold-const.h	2019-08-31 19:39:13.436366420 +0200
@@ -182,7 +182,7 @@ extern bool tree_expr_nonnegative_warnv_
 extern tree make_range (tree, int *, tree *, tree *, bool *);
 extern tree make_range_step (location_t, enum tree_code, tree, tree, tree,
 			     tree *, tree *, int *, bool *);
-extern tree range_check_type (tree);
+extern tree range_check_type (tree, bool = false);
 extern tree build_range_check (location_t, tree, tree, int, tree, tree);
 extern bool merge_ranges (int *, tree *, tree *, int, tree, tree, int,
 			  tree, tree);
--- gcc/fold-const.c.jj	2019-08-27 12:26:39.303884758 +0200
+++ gcc/fold-const.c	2019-08-31 19:39:06.235470312 +0200
@@ -4930,10 +4930,12 @@ maskable_range_p (const_tree low, const_
 }
 \f
 /* Helper routine for build_range_check and match.pd.  Return the type to
-   perform the check or NULL if it shouldn't be optimized.  */
+   perform the check or NULL if it shouldn't be optimized.
+   If UNSIGNEDP is true, the returned type must be unsigned, otherwise
+   it can be some INTEGER_TYPE that wraps around.  */
 
 tree
-range_check_type (tree etype)
+range_check_type (tree etype, bool unsignedp)
 {
   /* First make sure that arithmetics in this type is valid, then make sure
      that it wraps around.  */
@@ -4941,7 +4943,8 @@ range_check_type (tree etype)
     etype = lang_hooks.types.type_for_size (TYPE_PRECISION (etype),
 					    TYPE_UNSIGNED (etype));
 
-  if (TREE_CODE (etype) == INTEGER_TYPE && !TYPE_OVERFLOW_WRAPS (etype))
+  if (unsignedp
+      || (TREE_CODE (etype) == INTEGER_TYPE && !TYPE_OVERFLOW_WRAPS (etype)))
     {
       tree utype, minv, maxv;
 


	Jakub