Jeff Law wrote: > This patch converts the xstormy16 patch to LRA. It introduces a code > quality regression in the shiftsi testcase, but it also fixes numerous > aborts/errors. IMHO it's a good tradeoff.
I've investigated the shiftsi regression on xstormy16 and the underlying cause appears to be an interaction between lower-subreg's "subreg3" pass and the new LRA. Previously, reload was not phased by the "clobbers" that are introduced by the decompose_multiword_subregs function, but they appear to interfere with LRA's register assignments. combine's make_extra_copies introduces a new pseudo-to-pseudo move, but when subreg3 inserts a naked clobber between the original and the new move, LRA is recombine theses pseudos back to the same allocno. The shiftsi.cc regression on xstormy16 is fixed by adding -fno-split-wide-types. In fact, if all the regression tests pass, I'd suggest that flag_split_wide-types = false should be the default on xstormy16 now that we've moved to LRA. And if this works for xstormy16, it might be useful to other targets for the LRA transition; it's a difference in behaviour between reload and LRA that could potentially affect multiple targets. For reference, xstormy16 has a post-reload define_insn_and_split for movsi (i.e. a multi-word move). If this insn was split during split1 (i.e. before subreg3) there wouldn't be a problem (no clobber), but alas the target's xstormy16_split_move function has several asserts insisting this only get called when reload_completed. I hope this is useful. Cheers, Roger --
