diff --git a/lib/CodeGen/SplitKit.cpp b/lib/CodeGen/SplitKit.cpp index 149def33bdc..5f7fdccfb6a 100644 --- a/lib/CodeGen/SplitKit.cpp +++ b/lib/CodeGen/SplitKit.cpp @@ -20,6 +20,7 @@ #include "llvm/CodeGen/LiveIntervalAnalysis.h" #include "llvm/CodeGen/MachineDominators.h" #include "llvm/CodeGen/MachineInstrBuilder.h" +#include "llvm/CodeGen/MachineLoopInfo.h" #include "llvm/CodeGen/MachineRegisterInfo.h" #include "llvm/Support/Debug.h" #include "llvm/Support/raw_ostream.h" @@ -635,6 +636,60 @@ void SplitEditor::removeBackCopies(SmallVectorImpl &Copies) { } } +MachineBasicBlock* +SplitEditor::findShallowDominator(MachineBasicBlock *MBB, + MachineBasicBlock *DefMBB) { + if (MBB == DefMBB) + return MBB; + assert(MDT.dominates(DefMBB, MBB) && "MBB must be dominated by the def."); + + const MachineLoopInfo &Loops = SA.Loops; + const MachineLoop *DefLoop = Loops.getLoopFor(DefMBB); + MachineDomTreeNode *DefDomNode = MDT[DefMBB]; + + // Best candidate so far. + MachineBasicBlock *BestMBB = MBB; + unsigned BestDepth = UINT_MAX; + + for (;;) { + const MachineLoop *Loop = Loops.getLoopFor(MBB); + + // MBB isn't in a loop, it doesn't get any better. All dominators have a + // higher frequency by definition. + if (!Loop) { + DEBUG(dbgs() << "Def in BB#" << DefMBB->getNumber() << " dominates BB#" + << MBB->getNumber() << " at depth 0\n"); + return MBB; + } + + // We'll never be able to exit the DefLoop. + if (Loop == DefLoop) { + DEBUG(dbgs() << "Def in BB#" << DefMBB->getNumber() << " dominates BB#" + << MBB->getNumber() << " in the same loop\n"); + return MBB; + } + + // Least busy dominator seen so far. + unsigned Depth = Loop->getLoopDepth(); + if (Depth < BestDepth) { + BestMBB = MBB; + BestDepth = Depth; + DEBUG(dbgs() << "Def in BB#" << DefMBB->getNumber() << " dominates BB#" + << MBB->getNumber() << " at depth " << Depth << '\n'); + } + + // Leave loop by going to the immediate dominator of the loop header. + // This is a bigger stride than simply walking up the dominator tree. + MachineDomTreeNode *IDom = MDT[Loop->getHeader()]->getIDom(); + + // Too far up the dominator tree? + if (!IDom || !MDT.dominates(DefDomNode, IDom)) + return BestMBB; + + MBB = IDom->getBlock(); + } +} + void SplitEditor::hoistCopiesForSize() { // Get the complement interval, always RegIdx 0. LiveInterval *LI = Edit->get(0); @@ -706,10 +761,14 @@ void SplitEditor::hoistCopiesForSize() { DomPair &Dom = NearestDom[i]; if (!Dom.first || Dom.second.isValid()) continue; - // This value needs a hoisted copy inserted at the end of Dom.second. + // This value needs a hoisted copy inserted at the end of Dom.first. + VNInfo *ParentVNI = Parent->getValNumInfo(i); + MachineBasicBlock *DefMBB = LIS.getMBBFromIndex(ParentVNI->def); + // Get a less loopy dominator than Dom.first. + Dom.first = findShallowDominator(Dom.first, DefMBB); SlotIndex Last = LIS.getMBBEndIdx(Dom.first).getPrevSlot(); Dom.second = - defFromParent(0, Parent->getValNumInfo(i), Last, *Dom.first, + defFromParent(0, ParentVNI, Last, *Dom.first, LIS.getLastSplitPoint(Edit->getParent(), Dom.first))->def; } diff --git a/lib/CodeGen/SplitKit.h b/lib/CodeGen/SplitKit.h index 5a294e50554..d8fc2122a3c 100644 --- a/lib/CodeGen/SplitKit.h +++ b/lib/CodeGen/SplitKit.h @@ -315,6 +315,11 @@ private: /// in the vector in the complement interval. void removeBackCopies(SmallVectorImpl &Copies); + /// getShallowDominator - Returns the least busy dominator of MBB that is + /// also dominated by DefMBB. Busy is measured by loop depth. + MachineBasicBlock *findShallowDominator(MachineBasicBlock *MBB, + MachineBasicBlock *DefMBB); + /// hoistCopiesForSize - Hoist back-copies to the complement interval in a /// way that minimizes code size. This implements the SM_Size spill mode. void hoistCopiesForSize();