https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63259
--- Comment #16 from thopre01 at gcc dot gnu.org --- (In reply to Oleg Endo from comment #15) > (In reply to thopre01 from comment #14) > > > You mean with the added bswaphi2 pattern the pattern is still unchanged? > > > > After adding bswaphi2, the bswap pass does the transformation. Except for > the non-working 'signed short' mentioned above. But we already figured that > out earlier. Did we? All I can find is you and Andreas mentionning that it should work because it will be sign extended to int when doing the bitwise AND with 0xFF00. What did I miss? > > The expected sequence for the function above is: > > rts > swap.b r4,r0 > > i.e. no anding and oring of lower/higher 16 bit word, since the swap.b insn > operates on a SImode value and does not alter the high 16 bits. Oh yeah right. > > > > > If you have a bswap instruction it seems better to define a pattern for that > > which the expander will use. That's the job of the bswap pass to detect a > > bswap, it shouldn't be done by combine. > > The combine parts I was talking about are to eliminate the anding and oring > of higher 16 bits when a 16 bit byte swap is done on a 32 bit value. I'm surprised that it's not the semantic of a bswaphi. Best regards, Thomas
