https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49263
--- Comment #38 from Oleg Endo <olegendo at gcc dot gnu.org> --- (In reply to Alexander Klepikov from comment #37) > > As far as I understand from GCC sources, function I patched > 'expand_ashiftrt' process only constant values of shift. As you can see > earlier, I added your and other examples to tests. OK, thanks for the additional test cases. It really looks like the way the constant shift is expanded (via ashrsi3_n insn) on SH1/SH2 is getting in the way. The tst insn is mainly formed by the combine pass, which relies on certain insn patterns and combinations thereof. See also sh.md, around line 530. You can look at the debug output with the -fdump-rtl-all option to see what's happening in the RTL passes. What your patch is doing is to make it not emit the ashrsi3_n insn for constant shifts altogether? I guess it will make code that actually needs those real shifts larger, as it will always emit the whole shift stitching sequence. That might be a good thing or not. > It looks like really > dynamic shifts translate to library calls. So the option name '-mdisable-dynshift-libcall' doesn't make sense. What it actually does is more like '-mdisable-constshift-libcall'. > > Should I test more exotic situations? If so, could you please help me with > really exotic or weired examples? Have you had a look at the existing test cases for this in gcc/testsuite/gcc.target/sh ?
