On Thu, Nov 16, 2017 at 03:27:01PM +0000, Tamar Christina wrote:
> --- a/gcc/expr.c
> +++ b/gcc/expr.c
> @@ -2769,7 +2769,9 @@ copy_blkmode_to_reg (machine_mode mode, tree src)
>
> n_regs = (bytes + UNITS_PER_WORD - 1) / UNITS_PER_WORD;
> dst_words = XALLOCAVEC (rtx, n_regs);
> - bitsize = MIN (TYPE_ALIGN (TREE_TYPE (src)), BITS_PER_WORD);
> + bitsize = BITS_PER_WORD;
> + if (targetm.slow_unaligned_access (word_mode, TYPE_ALIGN (TREE_TYPE
> (src))))
> + bitsize = MIN (TYPE_ALIGN (TREE_TYPE (src)), BITS_PER_WORD);
>
> /* Copy the structure BITSIZE bits at a time. */
> for (bitpos = 0, xbitpos = padding_correction;
I believe this patch is wrong. Please revert. See the PR84762 testcase.
There are two problems. Firstly, if padding_correction is non-zero,
then xbitpos % BITS_PER_WORD is non-zero and in
store_bit_field (dst_word, bitsize, xbitpos % BITS_PER_WORD,
0, 0, word_mode,
extract_bit_field (src_word, bitsize,
bitpos % BITS_PER_WORD, 1,
NULL_RTX, word_mode, word_mode,
false, NULL),
false);
the stored bit-field exceeds the destination register size. You could
fix that by making bitsize the gcd of bitsize and padding_correction.
However, that doesn't fix the second problem which is that the
extracted bit-field can exceed the source size. That will result in
rubbish being read into a register.
--
Alan Modra
Australia Development Lab, IBM
