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Author SHA1 Message Date
Manman Ren adf4cc171e TBAA: update tbaa format from scalar format to struct-path aware format. 
llvm-svn: 191690
 2013-09-30 18:17:55 +00:00
Shuxin Yang 6e35094bbf Resurrect r191017 " GVN proceeds in the presence of dead code" plus a fix to PR17307 & 17308. 
The problem of r191017 is that when GVN fabricate a val-number for a dead instruction (in order
to make following expr-PRE happy), it forget to fabricate a leader-table entry for it as well.

llvm-svn: 191118
 2013-09-20 23:12:57 +00:00
Joerg Sonnenberger cf90a12170 Delete empty files. 
llvm-svn: 191105
 2013-09-20 20:40:22 +00:00
Joerg Sonnenberger 1fbe323649 Revert r191017, it results in segmentation faults in Qt. 
llvm-svn: 191104
 2013-09-20 20:33:57 +00:00
Shuxin Yang 74c9a170b8 GVN proceeds in the presence of dead code. 
This is how it ignores the dead code:
1) When a dead branch target, say block B, is identified, all the
    blocks dominated by B is dead as well.

2) The PHIs of those blocks in dominance-frontier(B) is updated such
   that the operands corresponding to dead predecessors are replaced
   by "UndefVal".

   Using lattice's jargon, the "UndefVal" is the "Top" in essence.
   Phi node like this "phi(v1 bb1, undef xx)" will be optimized into
   "v1" if v1 is constant, or v1 is an instruction which dominate this
   PHI node.

3) When analyzing the availability of a load L, all dead mem-ops which
   L depends on disguise as a load which evaluate exactly same value as L.

4) The dead mem-ops will be materialized as "UndefVal" during code motion.

llvm-svn: 191017
 2013-09-19 17:22:51 +00:00