Bernd Schmidt <ber...@codesourcery.com> writes: > This patch here: > http://gcc.gnu.org/ml/gcc-patches/2012-10/msg00661.html > > changed simplification code from > case TRUNCATE: > - /* We can't handle truncation to a partial integer mode here > - because we don't know the real bitsize of the partial > - integer mode. */ > - if (GET_MODE_CLASS (mode) == MODE_PARTIAL_INT) > - break; > > to > + if (GET_MODE_CLASS (mode) == MODE_PARTIAL_INT) > + { > + if (TRULY_NOOP_TRUNCATION_MODES_P (mode, GET_MODE (op))) > + return rtl_hooks.gen_lowpart_no_emit (mode, op); > + /* We can't handle truncation to a partial integer mode here > + because we don't know the real bitsize of the partial > + integer mode. */ > + break; > + } > > This is problematic for m32c; it defines TRULY_NOOP_TRUNCATION as 1, and > it's not really possible to define it meaningfully for partial int > modes, since it only gets passed precisions. Allowing subregs of PSImode > values leads to out of registers reload failures, so it kind of relies > on the previous behaviour.
Argh, that's unfortunate. The point of that change was to make simplify_gen_unary (TRUNCATE, ...) no worse than using a subreg. Would the equivalent lowpart simplify_gen_subreg call succeed (return nonnull)? If so, I think we want truncate to do the same. What simplification is this blocking, and why does it lead to reload failures? Thanks, Richard
