Initilize the machine LICM CSE map upon the first time an instruction is hoisted to

the loop preheader. Add instructions which are already in the preheader block that
may be common expressions of those that are hoisted out. These does get a few more
instructions CSE'ed.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85799 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 46 insertions, 17 deletions

diff --git a/lib/CodeGen/MachineLICM.cpp b/lib/CodeGen/MachineLICM.cpp
index 7b64047..1306aa6 100644
--- a/lib/CodeGen/MachineLICM.cpp
+++ b/lib/CodeGen/MachineLICM.cpp
@@ -56,12 +56,12 @@ namespace {
 
     // State that is updated as we process loops
     bool         Changed;          // True if a loop is changed.
+    bool         FirstInLoop;      // True if it's the first LICM in the loop.
     MachineLoop *CurLoop;          // The current loop we are working on.
     MachineBasicBlock *CurPreheader; // The preheader for CurLoop.
 
-    // For each BB and opcode pair, keep a list of hoisted instructions.
-    DenseMap<std::pair<unsigned, unsigned>,
-      std::vector<const MachineInstr*> > CSEMap;
+    // For each opcode, keep a list of potentail CSE instructions.
+    DenseMap<unsigned, std::vector<const MachineInstr*> > CSEMap;
   public:
     static char ID; // Pass identification, replacement for typeid
     MachineLICM() : MachineFunctionPass(&ID) {}
@@ -115,6 +115,11 @@ namespace {
     /// that is safe to hoist, this instruction is called to do the dirty work.
     ///
     void Hoist(MachineInstr *MI);
+
+    /// InitCSEMap - Initialize the CSE map with instructions that are in the
+    /// current loop preheader that may become duplicates of instructions that
+    /// are hoisted out of the loop.
+    void InitCSEMap(MachineBasicBlock *BB);
   };
 } // end anonymous namespace
 
@@ -140,7 +145,7 @@ static bool LoopIsOuterMostWithPreheader(MachineLoop *CurLoop) {
 bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
   DEBUG(errs() << "******** Machine LICM ********\n");
 
-  Changed = false;
+  Changed = FirstInLoop = false;
   TM = &MF.getTarget();
   TII = TM->getInstrInfo();
   TRI = TM->getRegisterInfo();
@@ -152,8 +157,7 @@ bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
   DT = &getAnalysis<MachineDominatorTree>();
   AA = &getAnalysis<AliasAnalysis>();
 
-  for (MachineLoopInfo::iterator
-         I = LI->begin(), E = LI->end(); I != E; ++I) {
+  for (MachineLoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) {
     CurLoop = *I;
 
     // Only visit outer-most preheader-sporting loops.
@@ -170,7 +174,11 @@ bool MachineLICM::runOnMachineFunction(MachineFunction &MF) {
     if (!CurPreheader)
       continue;
 
+    // CSEMap is initialized for loop header when the first instruction is
+    // being hoisted.
+    FirstInLoop = true;
     HoistRegion(DT->getNode(CurLoop->getHeader()));
+    CSEMap.clear();
   }
 
   return Changed;
@@ -191,10 +199,7 @@ void MachineLICM::HoistRegion(MachineDomTreeNode *N) {
   for (MachineBasicBlock::iterator
          MII = BB->begin(), E = BB->end(); MII != E; ) {
     MachineBasicBlock::iterator NextMII = MII; ++NextMII;
-    MachineInstr &MI = *MII;
-
-    Hoist(&MI);
-
+    Hoist(&*MII);
     MII = NextMII;
   }
 
@@ -430,6 +435,27 @@ MachineInstr *MachineLICM::ExtractHoistableLoad(MachineInstr *MI) {
   return NewMIs[0];
 }
 
+void MachineLICM::InitCSEMap(MachineBasicBlock *BB) {
+  for (MachineBasicBlock::iterator I = BB->begin(),E = BB->end(); I != E; ++I) {
+    const MachineInstr *MI = &*I;
+    // FIXME: For now, only hoist re-materilizable instructions. LICM will
+    // increase register pressure. We want to make sure it doesn't increase
+    // spilling.
+    if (TII->isTriviallyReMaterializable(MI, AA)) {
+      unsigned Opcode = MI->getOpcode();
+      DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator
+        CI = CSEMap.find(Opcode);
+      if (CI != CSEMap.end())
+        CI->second.push_back(MI);
+      else {
+        std::vector<const MachineInstr*> CSEMIs;
+        CSEMIs.push_back(MI);
+        CSEMap.insert(std::make_pair(Opcode, CSEMIs));
+      }
+    }
+  }
+}
+
 /// Hoist - When an instruction is found to use only loop invariant operands
 /// that are safe to hoist, this instruction is called to do the dirty work.
 ///
@@ -454,11 +480,14 @@ void MachineLICM::Hoist(MachineInstr *MI) {
       errs() << "\n";
     });
 
+  // If this is the first instruction being hoisted to the preheader,
+  // initialize the CSE map with potential common expressions.
+  InitCSEMap(CurPreheader);
+
   // Look for opportunity to CSE the hoisted instruction.
-  std::pair<unsigned, unsigned> BBOpcPair =
-    std::make_pair(CurPreheader->getNumber(), MI->getOpcode());
-  DenseMap<std::pair<unsigned, unsigned>,
-    std::vector<const MachineInstr*> >::iterator CI = CSEMap.find(BBOpcPair);
+  unsigned Opcode = MI->getOpcode();
+  DenseMap<unsigned, std::vector<const MachineInstr*> >::iterator
+    CI = CSEMap.find(Opcode);
   bool DoneCSE = false;
   if (CI != CSEMap.end()) {
     const MachineInstr *Dup = LookForDuplicate(MI, CI->second, RegInfo);
@@ -477,15 +506,15 @@ void MachineLICM::Hoist(MachineInstr *MI) {
 
   // Otherwise, splice the instruction to the preheader.
   if (!DoneCSE) {
-    CurPreheader->splice(CurPreheader->getFirstTerminator(),
-                         MI->getParent(), MI);
+    CurPreheader->splice(CurPreheader->getFirstTerminator(),MI->getParent(),MI);
+
     // Add to the CSE map.
     if (CI != CSEMap.end())
       CI->second.push_back(MI);
     else {
       std::vector<const MachineInstr*> CSEMIs;
       CSEMIs.push_back(MI);
-      CSEMap.insert(std::make_pair(BBOpcPair, CSEMIs));
+      CSEMap.insert(std::make_pair(Opcode, CSEMIs));
     }
   }