[MachineSink] Lower SplitEdgeProbabilityThreshold

Lower it slightly below the likeliness of a null-check to be true which
is set to 37.5% (see PtrUntakenProb).
Otherwise, it will split the edge and create another basic-block and
with an unconditional branch which might make the CFG more complex and
with a suboptimal block placement.
Note that if multiple instructions can be sinked from the same edge then
a split will occur regardless of this change.

Author: guy-david

llvm/lib/CodeGen/MachineSink.cpp

@@ -82,7 +82,7 @@ static cl::opt<unsigned> SplitEdgeProbabilityThreshold(
         "If the branch threshold is higher than this threshold, we allow "
         "speculative execution of up to 1 instruction to avoid branching to "
         "splitted critical edge"),
-    cl::init(40), cl::Hidden);
+    cl::init(35), cl::Hidden);
 
 static cl::opt<unsigned> SinkLoadInstsPerBlockThreshold(
     "machine-sink-load-instrs-threshold",