fold-const: Fix up make_range_step [PR105189]

[gcc.git] / gcc / fold-const.cc

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index fb08fa1dbc60851eee17daa7e890d951e7e89b81..7226bc5af01a8ce662827ef0bad813dddc06ff31 100644 (file)
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -5212,7 +5212,7 @@ make_range_step (location_t loc, enum tree_code code, tree arg0, tree arg1,
        n_high = fold_convert_loc (loc, arg0_type, n_high);
 
       /* If we're converting arg0 from an unsigned type, to exp,
-        a signed type,  we will be doing the comparison as unsigned.
+        a signed type, we will be doing the comparison as unsigned.
         The tests above have already verified that LOW and HIGH
         are both positive.
 
@@ -5274,6 +5274,32 @@ make_range_step (location_t loc, enum tree_code code, tree arg0, tree arg1,
            }
        }
 
+      /* Otherwise, if we are converting arg0 from signed type, to exp,
+        an unsigned type, we will do the comparison as signed.  If
+        high is non-NULL, we punt above if it doesn't fit in the signed
+        type, so if we get through here, +[-, high] or +[low, high] are
+        equivalent to +[-, n_high] or +[n_low, n_high].  Similarly,
+        +[-, -] or -[-, -] are equivalent too.  But if low is specified and
+        high is not, the +[low, -] range is equivalent to union of
+        +[n_low, -] and +[-, -1] ranges, so +[low, -] is equivalent to
+        -[0, n_low-1] and similarly -[low, -] to +[0, n_low-1], except for
+        low being 0, which should be treated as [-, -].  */
+      else if (TYPE_UNSIGNED (exp_type)
+              && !TYPE_UNSIGNED (arg0_type)
+              && low
+              && !high)
+       {
+         if (integer_zerop (low))
+           n_low = NULL_TREE;
+         else
+           {
+             n_high = fold_build2_loc (loc, PLUS_EXPR, arg0_type,
+                                       n_low, build_int_cst (arg0_type, -1));
+             n_low = build_zero_cst (arg0_type);
+             in_p = !in_p;
+           }
+       }
+
       *p_low = n_low;
       *p_high = n_high;
       *p_in_p = in_p;