C++ PATCH to fix ICE with vector expr folding (PR c++/83659)

[Marek Polacek]

Here we are crashing because cxx_fold_indirect_ref got a POINTER_PLUS_EXPR
with offset > signed HOST_WIDE_INT and we tried to convert it to sHWI.

The matching code in fold_indirect_ref_1 uses uHWIs so I've followed suit.
But that code now also uses poly_uint64 and I'm not sure if any of the
constexpr.c code should use it, too.  But this patch fixes the ICE.

Bootstrapped/regtested on x86_64-linux, ok for trunk/7?

2018-01-03  Marek Polacek  <pola...@redhat.com>

        PR c++/83659
        * constexpr.c (cxx_fold_indirect_ref): Use unsigned HOST_WIDE_INT
        when computing offsets.

        * g++.dg/torture/pr83659.C: New test.

diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c
index 1aeacd51810..cf7c994b381 100644
--- gcc/cp/constexpr.c
+++ gcc/cp/constexpr.c
@@ -3109,9 +3109,10 @@ cxx_fold_indirect_ref (location_t loc, tree type, tree 
op0, bool *empty_base)
              && (same_type_ignoring_top_level_qualifiers_p
                  (type, TREE_TYPE (op00type))))
            {
-             HOST_WIDE_INT offset = tree_to_shwi (op01);
+             unsigned HOST_WIDE_INT offset = tree_to_uhwi (op01);
              tree part_width = TYPE_SIZE (type);
-             unsigned HOST_WIDE_INT part_widthi = tree_to_shwi 
(part_width)/BITS_PER_UNIT;
+             unsigned HOST_WIDE_INT part_widthi
+               = tree_to_uhwi (part_width) / BITS_PER_UNIT;
              unsigned HOST_WIDE_INT indexi = offset * BITS_PER_UNIT;
              tree index = bitsize_int (indexi);
 
diff --git gcc/testsuite/g++.dg/torture/pr83659.C 
gcc/testsuite/g++.dg/torture/pr83659.C
index e69de29bb2d..d9f709bb520 100644
--- gcc/testsuite/g++.dg/torture/pr83659.C
+++ gcc/testsuite/g++.dg/torture/pr83659.C
@@ -0,0 +1,11 @@
+// PR c++/83659
+// { dg-do compile }
+
+typedef int V __attribute__ ((__vector_size__ (16)));
+V a;
+
+int
+main ()
+{
+  reinterpret_cast <int *> (&a)[-1] += 1;
+}

        Marek