------- Additional Comments From steven at gcc dot gnu dot org 2005-01-24
00:34 -------
For the RTL illiterate like myself:
BB2: j = k + l
j0 = j + 1
flags = (j0 <= 0)
if (flags) goto BB4 else goto BB3
flags are in live_at_end
BB3: flags are not in live_at_start
j = j + 2 [ kills the flags ]
goto BB5
flags are not in live_at_end
BB4: flags are in live_at_start
j = (flags) ? j : j0
goto BB5
flags are not in live_at_end
BB5: just an uninteresting join block
Then if-conversion basically merges BB2, BB3, and BB4 to give:
BB2: j = k + l
j0 = j + 1
r65 = j + 2 [ kills the flags ]
r66 = (flags) ? j : j0
flags = (j0 <= 0)
j = (flags) ? r66 : r65
falthru to BB5
BB5: just an uninteresting former join block
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19579
