Split around single instructions to enable register class inflation.
Normally, we don't create a live range for a single instruction in a
basic block, the spiller does that anyway. However, when splitting a
live range that belongs to a proper register sub-class, inserting these
extra COPY instructions completely remove the constraints from the
remainder interval, and it may be allocated from the larger super-class.
The spiller will mop up these small live ranges if we end up spilling
anyway. It calls them snippets.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@136989 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SplitKit.cpp b/lib/CodeGen/SplitKit.cpp
index e6bcfcd..cc85771 100644
--- a/lib/CodeGen/SplitKit.cpp
+++ b/lib/CodeGen/SplitKit.cpp
@@ -1087,6 +1087,24 @@
// Single Block Splitting
//===----------------------------------------------------------------------===//
+bool SplitAnalysis::shouldSplitSingleBlock(const BlockInfo &BI,
+ bool SingleInstrs) const {
+ // Always split for multiple instructions.
+ if (!BI.isOneInstr())
+ return true;
+ // Don't split for single instructions unless explicitly requested.
+ if (!SingleInstrs)
+ return false;
+ // Splitting a live-through range always makes progress.
+ if (BI.LiveIn && BI.LiveOut)
+ return true;
+ // No point in isolating a copy. It has no register class constraints.
+ if (LIS.getInstructionFromIndex(BI.FirstInstr)->isCopyLike())
+ return false;
+ // Finally, don't isolate an end point that was created by earlier splits.
+ return isOriginalEndpoint(BI.FirstInstr);
+}
+
/// getMultiUseBlocks - if CurLI has more than one use in a basic block, it
/// may be an advantage to split CurLI for the duration of the block.
bool SplitAnalysis::getMultiUseBlocks(BlockPtrSet &Blocks) {