[gcc r13-4405] tree-chrec: Fix up ICE on pointer multiplication [PR107835]

[gcc r13-4405] tree-chrec: Fix up ICE on pointer multiplication [PR107835]

[Jakub Jelinek]

https://gcc.gnu.org/g:7716ee1e90412f785cba20acffd59fc7461302cb

commit r13-4405-g7716ee1e90412f785cba20acffd59fc7461302cb
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Nov 30 11:44:27 2022 +0100

    tree-chrec: Fix up ICE on pointer multiplication [PR107835]
    
    r13-254-gdd3c7873a61019e9 added an optimization for {a, +, a} (x-1),
    but as can be seen on the following testcase, the way it is written
    where chrec_fold_multiply is called with type doesn't work for pointers:
                 res = build_int_cst (TREE_TYPE (x), 1);
                 res = chrec_fold_plus (TREE_TYPE (x), x, res);
                 res = chrec_convert_rhs (type, res, NULL);
                 res = chrec_fold_multiply (type, chrecr, res);
    while what we were doing before and what is still used if the condition
    doesn't match is fine:
                 res = chrec_convert_rhs (TREE_TYPE (chrecr), x, NULL);
                 res = chrec_fold_multiply (TREE_TYPE (chrecr), chrecr, res);
                 res = chrec_fold_plus (type, CHREC_LEFT (chrec), res);
    because it performs chrec_fold_multiply on TREE_TYPE (chrecr) and converts
    only afterwards.
    
    I think the easiest fix is to ignore the new path for pointer types.
    
    2022-11-30  Jakub Jelinek  <jakub@redhat.com>
    
            PR tree-optimization/107835
            * tree-chrec.cc (chrec_apply): Don't handle "{a, +, a} (x-1)"
            as "a*x" if type is a pointer type.
    
            * gcc.c-torture/compile/pr107835.c: New test.

Diff:
---
 gcc/testsuite/gcc.c-torture/compile/pr107835.c | 11 +++++++++++
 gcc/tree-chrec.cc                              |  3 ++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.c-torture/compile/pr107835.c b/gcc/testsuite/gcc.c-torture/compile/pr107835.c
new file mode 100644
index 00000000000..122beff2f11
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr107835.c
@@ -0,0 +1,11 @@
+/* PR tree-optimization/107835 */
+
+int *
+foo (void)
+{
+  int *x = 0;
+  unsigned n = n;
+  for (; n; --n, ++x)
+    ;
+  return x;
+}
diff --git a/gcc/tree-chrec.cc b/gcc/tree-chrec.cc
index 7321fb9d282..dcf26cbae84 100644
--- a/gcc/tree-chrec.cc
+++ b/gcc/tree-chrec.cc
@@ -622,7 +622,8 @@ chrec_apply (unsigned var,
 	  /* "{a, +, b} (x)"  ->  "a + b*x".  */
 	  else if (operand_equal_p (CHREC_LEFT (chrec), chrecr)
 		   && TREE_CODE (x) == PLUS_EXPR
-		   && integer_all_onesp (TREE_OPERAND (x, 1)))
+		   && integer_all_onesp (TREE_OPERAND (x, 1))
+		   && !POINTER_TYPE_P (type))
 	    {
 	      /* We know the number of iterations can't be negative.
 		 So {a, +, a} (x-1) -> "a*x".  */