From: Jakob Stoklund Olesen Date: Fri, 5 Aug 2011 22:20:45 +0000 (+0000) Subject: Split around single instructions to enable register class inflation. X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=2d6d86be84ee355223ccd20b7f87a0c9971c50c9;p=oota-llvm.git 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/RegAllocGreedy.cpp b/lib/CodeGen/RegAllocGreedy.cpp index 87b12c687ef..90d3810437e 100644 --- a/lib/CodeGen/RegAllocGreedy.cpp +++ b/lib/CodeGen/RegAllocGreedy.cpp @@ -942,6 +942,12 @@ void RAGreedy::splitAroundRegion(LiveRangeEdit &LREdit, DEBUG(dbgs() << "splitAroundRegion with " << NumGlobalIntvs << " globals.\n"); assert(NumGlobalIntvs && "No global intervals configured"); + // Isolate even single instructions when dealing with a proper sub-class. + // That giarantees register class inflation for the stack interval because it + // is all copies. + unsigned Reg = SA->getParent().reg; + bool SingleInstrs = RegClassInfo.isProperSubClass(MRI->getRegClass(Reg)); + // First handle all the blocks with uses. ArrayRef UseBlocks = SA->getUseBlocks(); for (unsigned i = 0; i != UseBlocks.size(); ++i) { @@ -971,7 +977,7 @@ void RAGreedy::splitAroundRegion(LiveRangeEdit &LREdit, // Create separate intervals for isolated blocks with multiple uses. if (!IntvIn && !IntvOut) { DEBUG(dbgs() << "BB#" << BI.MBB->getNumber() << " isolated.\n"); - if (!BI.isOneInstr()) + if (SA->shouldSplitSingleBlock(BI, SingleInstrs)) SE->splitSingleBlock(BI); continue; } diff --git a/lib/CodeGen/SplitKit.cpp b/lib/CodeGen/SplitKit.cpp index e6bcfcdfe31..cc85771d3dc 100644 --- a/lib/CodeGen/SplitKit.cpp +++ b/lib/CodeGen/SplitKit.cpp @@ -1087,6 +1087,24 @@ void SplitEditor::finish(SmallVectorImpl *LRMap) { // 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) { diff --git a/lib/CodeGen/SplitKit.h b/lib/CodeGen/SplitKit.h index 33c3c07eb43..8bed2a0fb67 100644 --- a/lib/CodeGen/SplitKit.h +++ b/lib/CodeGen/SplitKit.h @@ -185,6 +185,16 @@ public: typedef SmallPtrSet BlockPtrSet; + /// shouldSplitSingleBlock - Returns true if it would help to create a local + /// live range for the instructions in BI. There is normally no benefit to + /// creating a live range for a single instruction, but it does enable + /// register class inflation if the instruction has a restricted register + /// class. + /// + /// @param BI The block to be isolated. + /// @param SingleInstrs True when single instructions should be isolated. + bool shouldSplitSingleBlock(const BlockInfo &BI, bool SingleInstrs) const; + /// getMultiUseBlocks - Add basic blocks to Blocks that may benefit from /// having CurLI split to a new live interval. Return true if Blocks can be /// passed to SplitEditor::splitSingleBlocks.