The following avoids UB when computing the start value of the epilog
IV value which we compute as init + step * vect-niters where
the step * vect-niters computation can overflow.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
PR tree-optimization/127588
* tree-vect-loop-mainp.cc (vect_update_ivs_after_vectorizer):
Use an unsigned type to compute the epilog start value.
* gcc.dg/vect/vect-iv-15.c: New testcase.
---
gcc/testsuite/gcc.dg/vect/vect-iv-15.c | 25 +++++++++++++++++++++++++
gcc/tree-vect-loop-manip.cc | 26 ++++++++++++++------------
2 files changed, 39 insertions(+), 12 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/vect/vect-iv-15.c
diff --git a/gcc/testsuite/gcc.dg/vect/vect-iv-15.c
b/gcc/testsuite/gcc.dg/vect/vect-iv-15.c
new file mode 100644
index 00000000000..912b18be75f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/vect-iv-15.c
@@ -0,0 +1,25 @@
+/* PR127588 */
+/* { dg-require-effective-target int32plus } */
+
+#include "tree-vect.h"
+
+int s;
+
+__attribute__((noipa))
+void foo (int init)
+{
+ s = init;
+ do {
+ s += 1074790400;
+ } while (s <= 1073741823);
+}
+
+int main ()
+{
+ check_vect ();
+
+ foo (-1264552634);
+ if (s != 1959818566)
+ __builtin_abort ();
+ return 0;
+}
diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index b54353399d9..9d22d87705b 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -2612,7 +2612,7 @@ vect_update_ivs_after_vectorizer (loop_vec_info
loop_vinfo,
gsi_next (&gsi), gsi_next (&gsi1))
{
tree init_expr;
- tree step_expr, off;
+ tree step_expr;
tree type;
tree var, ni, ni_name;
@@ -2648,17 +2648,19 @@ vect_update_ivs_after_vectorizer (loop_vec_info
loop_vinfo,
if (induction_type == vect_step_op_add)
{
- tree stype = TREE_TYPE (step_expr);
- off = fold_build2 (MULT_EXPR, stype,
- fold_convert (stype, niters), step_expr);
-
- if (POINTER_TYPE_P (type))
- ni = fold_build_pointer_plus (init_expr, off);
- else
- ni = fold_convert (type,
- fold_build2 (PLUS_EXPR, stype,
- fold_convert (stype, init_expr),
- off));
+ /* Use an unsigned type because we compute 'off' without
+ accounting for 'init_expr', thus the computation might
+ overflow. Note we can also have FP inductions. */
+ tree ctype = (INTEGRAL_TYPE_P (TREE_TYPE (step_expr))
+ ? unsigned_type_for (TREE_TYPE (step_expr))
+ : TREE_TYPE (step_expr));
+ tree off = fold_build2 (MULT_EXPR, ctype,
+ fold_convert (ctype, niters),
+ fold_convert (ctype, step_expr));
+ ni = fold_convert (type,
+ fold_build2 (PLUS_EXPR, ctype,
+ fold_convert (ctype, init_expr),
+ off));
}
/* Don't bother call vect_peel_nonlinear_iv_init. */
else if (induction_type == vect_step_op_neg)
--
2.51.0
