[Bug rtl-optimization/19579] [3.3/3.4/4.0 regression] -march=i686 generates a bogus program for x86*

["steven at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- 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 
 

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19579