2015-02-27 1:45 GMT+03:00 Steven Bosscher <stevenb....@gmail.com>: > On Thu, Feb 26, 2015 at 8:35 PM, Georg-Johann Lay wrote: >> Take #2 introduces a new, avr-specific rtl pass whose sole purpose is to >> rectify notes. The pass is scheduled right before cfg does down (right >> before .*free_cfg) so that cfg and hence df machinery is available. >> >> Regression tests look fine and for the test case the patches produce correct >> code and correct insn length. > > Sorry for party-pooping, but it seems to me that the real bug is that > the target is lying to reload. > > IIUC the AVR port selects the insn alternative after register > allocation (after reload). It bases its selection on REG_DEAD notes. > In PR64331 an alternative is used that clobbers r20 that has a > REG_DEAD note, but r20 is not actually dead because hardreg-cprop has > propagated it forward without adjusting the note. > > The "normal" way of things is that the insn alternative is selected in > reload (or in LRA) and that the clobbers are added as necessary. In > PR64331, an alternative for insn r17 would be selected that has a > CLOBBER for r20, prevent hardreg-cprop from propagating r20. > > Selecting insns based on REG-notes is dangerous business. Lying to > reload and to post-RA passes is a mortal sin, the compiler will punish > you. There is no guarantee that nothing will change between your new > pass to recompute notes, and the final pass that emits the insns. > > It's not my port, for sure, but I would look for a real fix instead: > Don't select insns to output based on unreliable information like > REG-notes.
Steven rights. We will have an endless fight with this problem. Better to completely drop `reg_unused_after'. (I know that it used around 40 times in port) What do you think Georg ? Denis.
