Add function DominatorTree::getDescendants(). 

  As its name suggests, this function will return all basic blocks
dominated by a given block.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191014 91177308-0d34-0410-b5e6-96231b3b80d8
msbuild: Set _MSC_VER to match the CRT we're using

Various Windows SDK headers use _MSC_VER values to figure out what
version of the VC++ headers they're using, in particular for SAL macros.

Patch by Paul Hampson!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191015 91177308-0d34-0410-b5e6-96231b3b80d8
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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191017 91177308-0d34-0410-b5e6-96231b3b80d8
Fix a typo and simplify a boolean expression.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191018 91177308-0d34-0410-b5e6-96231b3b80d8
Remove unnecessary conditional operators performing bool->bool conversion.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191020 91177308-0d34-0410-b5e6-96231b3b80d8
X86 horizontal vector reduction cost model

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191021 91177308-0d34-0410-b5e6-96231b3b80d8