https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63783
--- Comment #20 from Michael Karcher <gcc-bugzilla at mkarcher dot dialup.fu-berlin.de> --- (In reply to Oleg Endo from comment #19) > > The or-then-SImode-compare optimization has an adverse effect on the test > > coverage, it seems. In both cases, GET_MODE(src_reg) and GET_MODE(dst_reg) > > are SImode, so the DImode output branch is not tested by any of your two > > example source files. > That is true as it stands now. However, we already anticipate that there > might be something going on with DImode stuff, so just adding the test might > help debugging in the future. Even if it doesn't add any value now, it > doesn't hurt anyone either. The test case is not a problem - but it would be helpful to have a testcase that actually tests the DImode output case. I understand that it likely is not possible with today's gcc to reach that branch, so it seems this has to stay the way it is now. I am fine with it. > > Furthermore, it looks like make_not_reg_insn will > > actually produce bad code if it were ever called with GET_MODE(src_reg) == > > DImode. > Please do explain. Of course. The instructions involving src_reg in make_not_reg_insn dealing with src_reg are completely quoted here: + // On SH we can do only SImode and DImode comparisons. + if (! (GET_MODE (src_reg) == SImode || GET_MODE (src_reg) == DImode)) + return NULL; In this fragment, you accept DImode source operands. So that code may be used to replace a DImode compare. + emit_insn (gen_rtx_SET (VOIDmode, m_ccreg, + gen_rtx_fmt_ee (EQ, SImode, src_reg, const0_rtx))); In this fragment, you are generating the replacement instruction, which is always an SImode compare. Maybe I miss the point, but I fail to undestand how an SImode compare might be acceptable on an DImode operand. Possibly, this even ICEs, I don't know enough about gcc internals to know what happens if src_reg is DImode which is passed to EQ in SImode.
