2014-12-19 15:21 GMT+00:00 Kenneth Zadeck <zad...@naturalbridge.com>: > > however, since i am a nice person .... > > loop-invariant solves the DF_UD_CHAIN which builds a data structure that > connects each use with all of the defs that reach it. I believe that this > is the opposite of what you want here. > > if you really need this, you need to also turn on the DF_DU_CHAIN which > builds the opposite structure. Both structures can be space hogs, but > they are both turned on in other places in the compiler so it is unlikely to > be an issue.
Exactly, Thanks, Kenneth. This approach works from my experiment and look much better than previous REG_NOTE approach. while it do have one problem. We need the UD/DU chain built before we do insn re-shuffling. While after re-shuffling, UD chain needs update, otherwise, the later "check_dependecies" in find_invariant_insn may fail. although we have re-shuffle instruction 1 into 2, the later check still using old UD info, thus decide instruction 2 is not iv. 1: regA <- vfp + regB 2: regA <- vfp + const my current fix is to insert those re-shuffled insn into a table named "vfp_const_iv", then skip those dependencies check for them as they don't have any dependencies. > > > >> >>>>> LOG_LINKs have nothing to do with single use; they point from the >>>>> _first_ >>>>> use to its corresponding def. >>>>> >>>>> You might want to look at what fwprop does instead. >>>> >>>> Pass rtl fwprop uses df information in single-definition way, it >>>> doesn't really take into consideration if register is a single use. >>>> This often corrupts other optimizations like post-increment and >>>> load/store pair. For example: >>>> >>>> add r2, r1, r0 >>>> ldr rx, [r2] >>>> add r2, r2, #4 >>>> is transformed into below form: >>>> add r2, r1, r0 >>>> ldr rx, [r1, r0] >>>> add r2, r2, #4 >>>> >>>> As a result, post-increment opportunity is corrupted, also definition >>>> of r2 can't be deleted because it's not single use. >>>> >>>> Thanks, >>>> bin >>> >>> thanks for all these suggestion. >>> >>> Have look at the LOG_LINK build function, a simple reverse scan, while >>> needs to allocate big map array for all pseudo regs. Haven't looked at >>> similar code in fwprop, >>> >>> actually, when found the first matched insn pattern, I just want to >>> scan several insns next, then abort quickly if nothing meet >>> requirement. there is no need to build full single-use information. >>> >>> still can anyone confirm that it is safe to re-use REG_DEAD info there >>> without calling df_note_add_problem and df_analysis first? or I am >>> using those info passed down from the previous pass which calculated >>> these info and maybe broken? >> >> It's not safe to use REG_DEAD info without re-computing it. > > not sure that reg_dead is the right answer even if you did re-compute it. > I believe you can have two parallel uses (on both sides of an if-then-else) > for a single def (above the if then else) and have two REG_DEAD notes. > >> Richard. > >