[PATCH] tree-optimization/108164 - undefined overflow with IV vectorization

[Richard Biener]

vect_update_ivs_after_vectorizer can end up emitting a signed
IV update when the loop body performed an unsigned computation.
The following makes sure to perform that update in the type
of the loop update type to avoid undefined behavior on overflow.

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

	PR tree-optimization/108164
	* tree-vect-loop-manip.cc (vect_update_ivs_after_vectorizer):
	Perform vect_step_op_add update in the appropriate type.

	* gcc.dg/pr108164.c: New testcase.
---
 gcc/testsuite/gcc.dg/pr108164.c | 19 +++++++++++++++++++
 gcc/tree-vect-loop-manip.cc     | 12 +++++++-----
 2 files changed, 26 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr108164.c

diff --git a/gcc/testsuite/gcc.dg/pr108164.c b/gcc/testsuite/gcc.dg/pr108164.c
new file mode 100644
index 00000000000..d76d557876e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr108164.c
@@ -0,0 +1,19 @@
+/* { dg-do run } */
+/* { dg-options "-O3 -fno-tree-dce" } */
+
+int a, b, c;
+int main()
+{
+  int e = -1;
+  short f = -1;
+  for (; c < 1; c++)
+    while (f >= e)
+      f++;
+  for (; a < 2; a++) {
+    short g = ~(~b | ~f);
+    int h = -g;
+    int i = (3 / ~h) / ~b;
+    b = i;
+  }
+  return 0;
+}
diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index 1d96130c985..5ec739ed218 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -1576,14 +1576,16 @@ vect_update_ivs_after_vectorizer (loop_vec_info loop_vinfo,
 
       if (induction_type == vect_step_op_add)
 	{
-	  off = fold_build2 (MULT_EXPR, TREE_TYPE (step_expr),
-			     fold_convert (TREE_TYPE (step_expr), niters),
-			     step_expr);
+	  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_build2 (PLUS_EXPR, type,
-			      init_expr, fold_convert (type, off));
+	    ni = fold_convert (type,
+			       fold_build2 (PLUS_EXPR, stype,
+					    fold_convert (stype, init_expr),
+					    off));
 	}
       /* Don't bother call vect_peel_nonlinear_iv_init.  */
       else if (induction_type == vect_step_op_neg)
-- 
2.35.3