Hi!
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.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2022-11-30 Jakub Jelinek <ja...@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.
--- gcc/tree-chrec.cc.jj 2022-05-10 18:33:14.641029951 +0200
+++ gcc/tree-chrec.cc 2022-11-29 15:24:41.810400368 +0100
@@ -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". */
--- gcc/testsuite/gcc.c-torture/compile/pr107835.c.jj 2022-11-29
15:31:32.565382590 +0100
+++ gcc/testsuite/gcc.c-torture/compile/pr107835.c 2022-11-29
15:31:15.795628304 +0100
@@ -0,0 +1,11 @@
+/* PR tree-optimization/107835 */
+
+int *
+foo (void)
+{
+ int *x = 0;
+ unsigned n = n;
+ for (; n; --n, ++x)
+ ;
+ return x;
+}
Jakub
