CodeGen: BlockPlacement: Reduce TriangleChainCount to 2

This produces a 1% speedup on an important internal Google benchmark
(protocol buffers), with no other regressions in google or in the llvm
test-suite. Only 5 targets in the entire llvm test-suite are affected,
and on those 5 targets the size increase is 0.027%

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297925 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed