On 02/19/2016 09:03 AM, Jakub Jelinek wrote:
As described in the PR, in C++ we can have assignments where both the lhs and rhs are COMPONENT_REFs with TREE_ADDRESSABLE types, including padding, but the FIELD_DECLs are artificial fields that have narrower bit sizes. store_field in this case takes the path of bit-field handling (even when it has bitpos and bitsize multiples of BITS_PER_UNIT (I think that is necessarily true for the TREE_ADDRESSABLE types), which is incorrect, because the rhs is expanded in that case through expand_normal, which for a result type wider than the FIELD_DECL with forces it into a temporary. In older GCCs that just generated inefficient code (copy the rhs into a stack temporary, then copy that to lhs), but GCC trunk ICEs on that. Fixed by not taking the bit-field path in that case after verifying we'll be able to expand it properly using the normal store_expr.
Won't store_expr clobber tail padding because it doesn't know about bitsize? I would think that what we want is to use emit_block_move in the bit-field path whenever we're dealing with whole bytes in memory.
Jason
