Implement single block splitting.

Before spilling a live range, we split it into a separate range for each basic
block where it is used. That way we only get one reload per basic block if the
new smaller ranges can allocate to a register.

This type of splitting is already present in the standard spiller.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110934 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/InlineSpiller.cpp

@@ -118,6 +118,15 @@ bool InlineSpiller::split() {
           .splitAroundLoop(loop))
       return true;
   }
+
+  // Try splitting into single block intervals.
+  SplitAnalysis::BlockPtrSet blocks;
+  if (splitAnalysis_.getMultiUseBlocks(blocks)) {
+    if (SplitEditor(splitAnalysis_, lis_, vrm_, *newIntervals_)
+          .splitSingleBlocks(blocks))
+      return true;
+  }
+
   return false;
 }