[gcc r11-10316] tree-optimization/106189 - avoid division by zero exception

[gcc r11-10316] tree-optimization/106189 - avoid division by zero exception

[Richard Biener]

https://gcc.gnu.org/g:9124675d2771aaf573bfbbe237ab28030bf3115d

commit r11-10316-g9124675d2771aaf573bfbbe237ab28030bf3115d
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Jul 25 17:24:57 2022 +0200

    tree-optimization/106189 - avoid division by zero exception
    
    The diagnostic code can end up with zero sized array elements
    with T[][0] and the wide-int code nicely avoids exceptions when
    dividing by zero in one codepath but not in another.  The following
    fixes the exception by using wide-int in both paths.
    
            PR tree-optimization/106189
            * gimple-array-bounds.cc (array_bounds_checker::check_mem_ref):
            Divide using offset_ints.
    
            * gcc.dg/pr106189.c: New testcase.
    
    (cherry picked from commit bb04f9f23ac0dee2c003118c85372ece50a52220)

Diff:
---
 gcc/gimple-array-bounds.cc      | 2 +-
 gcc/testsuite/gcc.dg/pr106189.c | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/gcc/gimple-array-bounds.cc b/gcc/gimple-array-bounds.cc
index b1179518651..8bcc0077b8c 100644
--- a/gcc/gimple-array-bounds.cc
+++ b/gcc/gimple-array-bounds.cc
@@ -783,7 +783,7 @@ array_bounds_checker::check_mem_ref (location_t location, tree ref,
   int i = 0;
   if (extrema[i] < -arrbounds[1] || extrema[i = 1] > ubound)
     {
-      HOST_WIDE_INT tmpidx = extrema[i].to_shwi () / eltsize.to_shwi ();
+      HOST_WIDE_INT tmpidx = (extrema[i] / eltsize).to_shwi ();
 
       if (warning_at (location, OPT_Warray_bounds,
 		      "intermediate array offset %wi is outside array bounds "
diff --git a/gcc/testsuite/gcc.dg/pr106189.c b/gcc/testsuite/gcc.dg/pr106189.c
new file mode 100644
index 00000000000..0eca8343c56
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr106189.c
@@ -0,0 +1,5 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Warray-bounds=2 -w" } */
+
+int a_n_0_0_a[][0];
+void a_n_0_0() { T(((char *)a_n_0_0_a)[1]); }