bswap: Fix up a thinko with empty CONSTRUCTORs [PR98378]

The code I've added recently in find_bswap_or_nop for VECTOR CONSTRUCTORs
is missing punt on an important case - namely empty CONSTRUCTORs, because in that
case the loop will not initialize *n and the code after the loop will then
use the uninitialized structure.

2020-12-19  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/98378
	* gimple-ssa-store-merging.c (find_bswap_or_nop): Punt if CONSTRUCTOR
	has no elements.

diff --git a/gcc/gimple-ssa-store-merging.c b/gcc/gimple-ssa-store-merging.c
index 2894205fa3c3f5e7b757fa5c4dacde353aafd20b..2ab51e23c077d7208ebaa4be5400aa8636a5d82a 100644 (file)
--- a/gcc/gimple-ssa-store-merging.c
+++ b/gcc/gimple-ssa-store-merging.c
@@ -873,6 +873,8 @@ find_bswap_or_nop (gimple *stmt, struct symbolic_number *n, bool *bswap)
       if (sz != 16 && sz != 32 && sz != 64)
        return NULL;
       tree rhs = gimple_assign_rhs1 (stmt);
+      if (CONSTRUCTOR_NELTS (rhs) == 0)
+       return NULL;
       tree eltype = TREE_TYPE (TREE_TYPE (rhs));
       unsigned HOST_WIDE_INT eltsz
        = int_size_in_bytes (eltype) * BITS_PER_UNIT;