https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78660
--- Comment #7 from YunQiang Su <syq at debian dot org> ---
(In reply to YunQiang Su from comment #6)
> With revert some change, with patch:
>
> Index: gcc-7-7-20161217/src/gcc/combine.c
> ===================================================================
> --- gcc-7-7-20161217.orig/src/gcc/combine.c
> +++ gcc-7-7-20161217/src/gcc/combine.c
> @@ -9972,13 +9972,13 @@ reg_nonzero_bits_for_combine (const_rtx
> (DF_LR_IN (ENTRY_BLOCK_PTR_FOR_FN (cfun)->next_bb),
> REGNO (x)))))
> {
> - /* Note that, even if the precision of last_set_mode is lower than
> that
> - of mode, record_value_for_reg invoked nonzero_bits on the register
> - with nonzero_bits_mode (because last_set_mode is necessarily
> integral
> - and HWI_COMPUTABLE_MODE_P in this case) so bits in nonzero_bits_mode
> - are all valid, hence in mode too since nonzero_bits_mode is defined
> - to the largest HWI_COMPUTABLE_MODE_P mode. */
> - *nonzero &= rsp->last_set_nonzero_bits;
> + unsigned HOST_WIDE_INT mask = rsp->last_set_nonzero_bits;
> +
> + if (GET_MODE_PRECISION (rsp->last_set_mode) < GET_MODE_PRECISION
> (mode))
> + /* We don't know anything about the upper bits. */
> + mask |= GET_MODE_MASK (mode) ^ GET_MODE_MASK (rsp->last_set_mode);
> +
> + *nonzero &= mask;
> return NULL;
> }
This can make it buildable now.
