[PATCH] middle-end/113576 - avoid out-of-bound vector element access

[Richard Biener]

The following avoids accessing out-of-bound vector elements when
native encoding a boolean vector with sub-BITS_PER_UNIT precision
elements.  The error was basing the number of elements to extract
on the rounded up total byte size involved and the patch bases
everything on the total number of elements to extract instead.

As a side-effect this now consistently results in zeros in the
padding of the last encoded byte which also avoids the failure
mode seen in PR113576.

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

OK?

Thanks,
Richard.

        PR middle-end/113576
        * fold-const.cc (native_encode_vector_part): Avoid accessing
        out-of-bound elements.
---
 gcc/fold-const.cc | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 80e211e18c0..8638757312b 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -8057,13 +8057,13 @@ native_encode_vector_part (const_tree expr, unsigned 
char *ptr, int len,
        off = 0;
 
       /* Zero the buffer and then set bits later where necessary.  */
-      int extract_bytes = MIN (len, total_bytes - off);
+      unsigned elts_per_byte = BITS_PER_UNIT / elt_bits;
+      unsigned first_elt = off * elts_per_byte;
+      unsigned extract_elts = MIN (len * elts_per_byte, count - first_elt);
+      unsigned extract_bytes = CEIL (elt_bits * extract_elts, BITS_PER_UNIT);
       if (ptr)
        memset (ptr, 0, extract_bytes);
 
-      unsigned int elts_per_byte = BITS_PER_UNIT / elt_bits;
-      unsigned int first_elt = off * elts_per_byte;
-      unsigned int extract_elts = extract_bytes * elts_per_byte;
       for (unsigned int i = 0; i < extract_elts; ++i)
        {
          tree elt = VECTOR_CST_ELT (expr, first_elt + i);
-- 
2.35.3