This is a regression caused by
https://gcc.gnu.org/cgit/gcc/commit/?id=62993cc9d2200ef7a05f317cdef3262996c0ac10,
which added variable trip count XOR final value replacement.
The XOR final-value replacement used tree_niter_desc::niter directly to
compute parity. That expression is valid only when may_be_zero is false.
For a do loop with zero latch executions, using it can produce an incorrect
parity. Use number_of_latch_executions instead, which incorporates the
may_be_zero condition, and bail out when it is not available.
PR tree-optimization/126994
gcc/ChangeLog:
* tree-scalar-evolution.cc (analyze_and_compute_bitop_with_inv_effect):
Use number_of_latch_executions for XOR parity.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/pr126994.c: New test.
Signed-off-by: Eikansh Gupta <[email protected]>
---
gcc/testsuite/gcc.dg/tree-ssa/pr126994.c | 31 ++++++++++++++++++++++++
gcc/tree-scalar-evolution.cc | 3 +++
2 files changed, 34 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr126994.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr126994.c
b/gcc/testsuite/gcc.dg/tree-ssa/pr126994.c
new file mode 100644
index 00000000000..d4cc421793c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr126994.c
@@ -0,0 +1,31 @@
+/* PR tree-optimization/126994 */
+/* { dg-do run } */
+/* { dg-options "-O1" } */
+
+long
+__attribute__ ((noipa))
+foo (int a)
+{
+ long c = 0;
+ int d = 0;
+ for (; a < 2; a++)
+ do
+ {
+ d++;
+ c ^= 3;
+ }
+ while (d < 2);
+ return c;
+}
+
+int
+main (void)
+{
+ if (foo (0) != 3)
+ __builtin_abort ();
+ if (foo (1) != 0)
+ __builtin_abort ();
+ if (foo (2) != 0)
+ __builtin_abort ();
+ return 0;
+}
diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc
index 0466a1d36b6..1a321eddc3d 100644
--- a/gcc/tree-scalar-evolution.cc
+++ b/gcc/tree-scalar-evolution.cc
@@ -3850,6 +3850,9 @@ analyze_and_compute_bitop_with_inv_effect (class loop*
loop, tree phidef,
if (code1 == BIT_XOR_EXPR)
{
+ niter = number_of_latch_executions (loop);
+ if (niter == chrec_dont_know)
+ return NULL_TREE;
tree niter_type = TREE_TYPE (niter);
tree one = build_one_cst (niter_type);
tree contributes = fold_build2 (BIT_XOR_EXPR, niter_type,
--
2.34.1
