[gcc r12-9065] tree-optimization/108164 - undefined overflow with IV vectorization

[Richard Biener <rguenth@gcc.gnu.org>]

https://gcc.gnu.org/g:50ef4fc8c848929ee79af97ac445a45baab7d575

commit r12-9065-g50ef4fc8c848929ee79af97ac445a45baab7d575
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Dec 19 14:55:45 2022 +0100

    tree-optimization/108164 - undefined overflow with IV vectorization
    
    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.
    
            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.
    
    (cherry picked from commit ec459469f8a75d96a9b26694554efcc900d411de)

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

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 e4381eb7079..cb5bb87ae33 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -1596,14 +1596,16 @@ vect_update_ivs_after_vectorizer (loop_vec_info loop_vinfo,
 
       init_expr = PHI_ARG_DEF_FROM_EDGE (phi, loop_preheader_edge (loop));
 
-      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));
 
       var = create_tmp_var (type, "tmp");