Add skeleton of a machine level cse pass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97543 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 124 insertions, 0 deletions

diff --git a/lib/CodeGen/MachineCSE.cpp b/lib/CodeGen/MachineCSE.cpp
new file mode 100644
index 0000000000..288fb47349
--- /dev/null
+++ b/lib/CodeGen/MachineCSE.cpp
@@ -0,0 +1,124 @@
+//===-- MachineCSE.cpp - Machine Common Subexpression Elimination Pass ----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs global common subexpression elimination on machine
+// instructions using a scoped hash table based value numbering schemem. IT
+// must be run while the machine function is still in SSA form.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "machine-cse"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/ADT/ScopedHashTable.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/Debug.h"
+
+using namespace llvm;
+
+namespace llvm {
+  template<> struct DenseMapInfo<MachineInstr*> {
+    static inline MachineInstr *getEmptyKey() {
+      return 0;
+    }
+
+    static inline MachineInstr *getTombstoneKey() {
+      return reinterpret_cast<MachineInstr*>(-1);
+    }
+
+    static unsigned getHashValue(const MachineInstr* const &MI) {
+      unsigned Hash = MI->getOpcode() * 37;
+      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+        const MachineOperand &MO = MI->getOperand(i);
+        uint64_t Key = (uint64_t)MO.getType() << 32;
+        switch (MO.getType()) {
+        default: break;
+        case MachineOperand::MO_Register:
+          Key |= MO.getReg();
+          break;
+        case MachineOperand::MO_Immediate:
+          Key |= MO.getImm();
+          break;
+        case MachineOperand::MO_FrameIndex:
+        case MachineOperand::MO_ConstantPoolIndex:
+        case MachineOperand::MO_JumpTableIndex:
+          Key |= MO.getIndex();
+          break;
+        case MachineOperand::MO_MachineBasicBlock:
+          Key |= DenseMapInfo<void*>::getHashValue(MO.getMBB());
+          break;
+        case MachineOperand::MO_GlobalAddress:
+          Key |= DenseMapInfo<void*>::getHashValue(MO.getGlobal());
+          break;
+        case MachineOperand::MO_BlockAddress:
+          Key |= DenseMapInfo<void*>::getHashValue(MO.getBlockAddress());
+          break;
+        }
+        Key += ~(Key << 32);
+        Key ^= (Key >> 22);
+        Key += ~(Key << 13);
+        Key ^= (Key >> 8);
+        Key += (Key << 3);
+        Key ^= (Key >> 15);
+        Key += ~(Key << 27);
+        Key ^= (Key >> 31);
+        Hash = (unsigned)Key + Hash * 37;
+      }
+      return Hash;
+    }
+
+    static bool isEqual(const MachineInstr* const &LHS,
+                        const MachineInstr* const &RHS) {
+      return LHS->isIdenticalTo(RHS);
+    }
+  };
+} // end llvm namespace
+
+namespace {
+  class MachineCSE : public MachineFunctionPass {
+    ScopedHashTable<MachineInstr*, unsigned> VNT;
+    MachineDominatorTree *DT;
+  public:
+    static char ID; // Pass identification
+    MachineCSE() : MachineFunctionPass(&ID) {}
+
+    virtual bool runOnMachineFunction(MachineFunction &MF);
+    
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesCFG();
+      MachineFunctionPass::getAnalysisUsage(AU);
+      AU.addRequired<MachineDominatorTree>();
+      AU.addPreserved<MachineDominatorTree>();
+    }
+
+  private:
+    bool ProcessBlock(MachineDomTreeNode *Node);
+  };
+} // end anonymous namespace
+
+char MachineCSE::ID = 0;
+static RegisterPass<MachineCSE>
+X("machine-cse", "Machine Common Subexpression Elimination");
+
+FunctionPass *llvm::createMachineCSEPass() { return new MachineCSE(); }
+
+bool MachineCSE::ProcessBlock(MachineDomTreeNode *Node) {
+  ScopedHashTableScope<MachineInstr*, unsigned> VNTS(VNT);
+  MachineBasicBlock *MBB = Node->getBlock();
+  for (MachineBasicBlock::iterator I = MBB->begin(), E = MBB->end(); I != E;
+       ++I) {
+  }
+  return false;
+}
+
+bool MachineCSE::runOnMachineFunction(MachineFunction &MF) {
+  DT = &getAnalysis<MachineDominatorTree>();
+  return ProcessBlock(DT->getRootNode());
+}