[PATCH] tree-optimization/122653 - handle POINTER_DIFF_EXPR in SCEV

[Richard Biener]

The following adds POINTER_DIFF_EXPR handling to SCEV stmt analysis,
mapping to conversions and MINUS_EXPR.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

        PR tree-optimization/122653
        * tree-scalar-evolution.cc (interpret_rhs_expr): Handle
        POINTER_DIFF_EXPR.

        * gcc.dg/tree-ssa/scev-16.c: New testcase.
---
 gcc/testsuite/gcc.dg/tree-ssa/scev-16.c | 19 +++++++++++++++++++
 gcc/tree-scalar-evolution.cc            | 14 ++++++++++++++
 2 files changed, 33 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/scev-16.c

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/scev-16.c 
b/gcc/testsuite/gcc.dg/tree-ssa/scev-16.c
new file mode 100644
index 00000000000..0cc7f703c53
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/scev-16.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-sccp" } */
+
+extern char a[];
+int foo ()
+{
+  int cnt = 0;
+  char *aend = a + 32;
+  char *a0 = a;
+  do
+    {
+      a0 = a0 + 16;
+      cnt++;
+    }
+  while (aend - a0 > 12);
+  return cnt;
+}
+
+/* { dg-final { scan-tree-dump "return 2" "sccp" } } */
diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc
index 180df75311f..626c201df5e 100644
--- a/gcc/tree-scalar-evolution.cc
+++ b/gcc/tree-scalar-evolution.cc
@@ -1753,6 +1753,20 @@ interpret_rhs_expr (class loop *loop, gimple *at_stmt,
       res = chrec_fold_plus (type, chrec1, chrec2);
       break;
 
+    case POINTER_DIFF_EXPR:
+      {
+       tree utype = unsigned_type_for (type);
+       chrec1 = analyze_scalar_evolution (loop, rhs1);
+       chrec2 = analyze_scalar_evolution (loop, rhs2);
+       chrec1 = chrec_convert (utype, chrec1, at_stmt);
+       chrec2 = chrec_convert (utype, chrec2, at_stmt);
+       chrec1 = instantiate_parameters (loop, chrec1);
+       chrec2 = instantiate_parameters (loop, chrec2);
+       res = chrec_fold_minus (utype, chrec1, chrec2);
+       res = chrec_convert (type, res, at_stmt);
+       break;
+      }
+
     case PLUS_EXPR:
       chrec1 = analyze_scalar_evolution (loop, rhs1);
       chrec2 = analyze_scalar_evolution (loop, rhs2);
-- 
2.51.0