[gcc/devel/c++-modules] tree-optimization/94234 - add pattern for ptr-diff on addresses with same offset

[Nathan Sidwell <nathan@gcc.gnu.org>]

https://gcc.gnu.org/g:459f6f68a75fe88e7c8309ca8ad3244a532b0d8e

commit 459f6f68a75fe88e7c8309ca8ad3244a532b0d8e
Author: Feng Xue <fxue@os.amperecomputing.com>
Date:   Mon Jun 1 11:57:35 2020 +0800

    tree-optimization/94234 - add pattern for ptr-diff on addresses with same offset
    
    2020-08-19  Feng Xue  <fxue@os.amperecomputing.com>
    
    gcc/
            PR tree-optimization/94234
            * match.pd ((PTR_A + OFF) - (PTR_B + OFF)) -> (PTR_A - PTR_B): New
            simplification.
    
    gcc/testsuite/
            PR tree-optimization/94234
            * gcc.dg/pr94234-1.c: New test.

Diff:
---
 gcc/match.pd                     |  3 +++
 gcc/testsuite/gcc.dg/pr94234-1.c | 15 +++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/gcc/match.pd b/gcc/match.pd
index c3b88168ac4..2cffcae3d8b 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2549,6 +2549,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 	     && TREE_CODE (@2) == INTEGER_CST
 	     && tree_int_cst_sign_bit (@2) == 0))
      (minus (convert @1) (convert @2)))))
+   (simplify
+    (pointer_diff (pointer_plus @0 @2) (pointer_plus @1 @2))
+     (pointer_diff @0 @1))
    (simplify
     (pointer_diff (pointer_plus @@0 @1) (pointer_plus @0 @2))
     /* The second argument of pointer_plus must be interpreted as signed, and
diff --git a/gcc/testsuite/gcc.dg/pr94234-1.c b/gcc/testsuite/gcc.dg/pr94234-1.c
new file mode 100644
index 00000000000..d85563b32da
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr94234-1.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-forwprop1" } */ 
+
+typedef __INTPTR_TYPE__ ssize_t;
+typedef __PTRDIFF_TYPE__ ptrdiff_t;
+
+ptrdiff_t foo (char *a, ssize_t n, ssize_t m)
+{
+  char *b1 = a + 8 * n;
+  char *b2 = a + 8 * (n + 1);
+
+  return (b1 + m) - (b2 + m);
+}
+
+/* { dg-final { scan-tree-dump-times "return -8;" 1 "forwprop1" } } */