tree-optimization/109791 - simplify (unsigned)&foo - (unsigned)(&foo + o)

The following adds another variant of address difference simplification.
The utility ptr_difference_const only handles constant differences
(we also cannot code generate anything else), so exposing a possible
POINTER_PLUS_EXPR in the match and computing the difference on the
base only makes it possible to handle one case of a variable offset.
This simplifies

(unsigned long) &MEM <char[3]> [(void *)&str + 2B] - (unsigned long) (&str + (_69 + 1))

down to (1 - (unsigned long) _69) during niter analysis, allowing
ranger to eliminate a condition later and avoiding a bogus
-Wstringop-overflow diagnostic for the testcase in the PR.

	PR tree-optimization/109791
	* match.pd (minus (convert ADDR_EXPR@0) (convert (pointer_plus @1 @2))):
	New pattern.
	(minus (convert (pointer_plus @1 @2)) (convert ADDR_EXPR@0)):
	Likewise.

diff --git a/gcc/match.pd b/gcc/match.pd
index b7f28ab074c2107d9799ad2ddf795e42f14e5ea1..2e46e074e9354e6be0f184785cda5dfa12a1434f 100644 (file)
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2572,6 +2572,18 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
    (bit_and @0 { algn; })))
 
 /* Try folding difference of addresses.  */
+(simplify
+ (minus (convert ADDR_EXPR@0) (convert (pointer_plus @1 @2)))
+ (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
+  (with { poly_int64 diff; }
+   (if (ptr_difference_const (@0, @1, &diff))
+    (minus { build_int_cst_type (type, diff); } (convert @2))))))
+(simplify
+ (minus (convert (pointer_plus @0 @2)) (convert ADDR_EXPR@1))
+ (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
+  (with { poly_int64 diff; }
+   (if (ptr_difference_const (@0, @1, &diff))
+    (plus (convert @2) { build_int_cst_type (type, diff); })))))
 (simplify
  (minus (convert ADDR_EXPR@0) (convert @1))
  (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))