A simple (spilling) register allocator.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4828 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/RegAllocSimple.cpp

@@ -0,0 +1,219 @@
+//===-- RegAllocSimple.cpp - A simple generic register allocator --- ------===//
+//
+// This file implements a simple register allocator. *Very* simple.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Function.h"
+#include "llvm/iTerminators.h"
+#include "llvm/Type.h"
+#include "llvm/Constants.h"
+#include "llvm/Pass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/Target/MRegisterInfo.h"
+#include "llvm/Target/MachineRegInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Support/InstVisitor.h"
+#include "Support/Statistic.h"
+#include <map>
+
+namespace {
+  struct RegAllocSimple : public FunctionPass {
+    TargetMachine &TM;
+    MachineBasicBlock *CurrMBB;
+    MachineFunction *MF;
+    unsigned maxOffset;
+    const MRegisterInfo *RegInfo;
+    unsigned NumBytesAllocated, ByteAlignment;
+    
+    // Maps SSA Regs => offsets on the stack where these values are stored
+    std::map<unsigned, unsigned> RegMap; // FIXME: change name to OffsetMap
+
+    // Maps SSA Regs => physical regs
+    std::map<unsigned, unsigned> SSA2PhysRegMap;
+    
+    // Maps RegClass => which index we can take a register from. Since this is a
+    // simple register allocator, when we need a register of a certain class, we
+    // just take the next available one.
+    std::map<unsigned, unsigned> RegsUsed;
+    std::map<const TargetRegisterClass*, unsigned> RegClassIdx;
+
+    RegAllocSimple(TargetMachine &tm) : TM(tm), CurrMBB(0), maxOffset(0), 
+                                        RegInfo(tm.getRegisterInfo()),
+                                        NumBytesAllocated(0), ByteAlignment(4)
+    {
+      RegsUsed[RegInfo->getFramePointer()] = 1;
+      RegsUsed[RegInfo->getStackPointer()] = 1;
+    }
+
+    bool isAvailableReg(unsigned Reg) {
+      // assert(Reg < MRegisterInfo::FirstVirtualReg && "...");
+      return RegsUsed.find(Reg) == RegsUsed.end();
+    }
+
+    /// Given size (in bytes), returns a register that is currently unused
+    /// Side effect: marks that register as being used until manually cleared
+    unsigned getFreeReg(unsigned virtualReg);
+
+    /// Returns all `borrowed' registers back to the free pool
+    void clearAllRegs() {
+        RegClassIdx.clear();
+    }
+
+    /// Moves value from memory into that register
+    MachineBasicBlock::iterator
+    moveUseToReg (MachineBasicBlock::iterator I, unsigned VirtReg,
+                  unsigned &PhysReg);
+
+    /// Saves reg value on the stack (maps virtual register to stack value)
+    MachineBasicBlock::iterator
+    saveRegToStack (MachineBasicBlock::iterator I, unsigned VirtReg,
+                    unsigned PhysReg);
+
+    /// runOnFunction - Top level implementation of instruction selection for
+    /// the entire function.
+    ///
+    bool runOnMachineFunction(MachineFunction &Fn);
+
+    bool runOnFunction(Function &Fn) {
+      return runOnMachineFunction(MachineFunction::get(&Fn));
+    }
+  };
+
+}
+
+unsigned RegAllocSimple::getFreeReg(unsigned virtualReg) {
+  const TargetRegisterClass* regClass = MF->getRegClass(virtualReg);
+  unsigned physReg;
+  assert(regClass);
+  if (RegClassIdx.find(regClass) != RegClassIdx.end()) {
+    unsigned regIdx = RegClassIdx[regClass]++;
+    assert(regIdx < regClass->getNumRegs() && "Not enough registers!");
+    physReg = regClass->getRegister(regIdx);
+  } else {
+    physReg = regClass->getRegister(0);
+    // assert(physReg < regClass->getNumRegs() && "No registers in class!");
+    RegClassIdx[regClass] = 1;
+  }
+
+  if (isAvailableReg(physReg))
+    return physReg;
+  else {
+    return getFreeReg(virtualReg);
+  }
+}
+
+MachineBasicBlock::iterator
+RegAllocSimple::moveUseToReg (MachineBasicBlock::iterator I,
+                              unsigned VirtReg, unsigned &PhysReg)
+{
+  const TargetRegisterClass* regClass = MF->getRegClass(VirtReg);
+  assert(regClass);
+
+  unsigned stackOffset;
+  if (RegMap.find(VirtReg) == RegMap.end()) {
+    unsigned size = regClass->getDataSize();
+    unsigned over = NumBytesAllocated - (NumBytesAllocated % ByteAlignment);
+    if (size >= ByteAlignment - over) {
+      // need to pad by (ByteAlignment - over)
+      NumBytesAllocated += ByteAlignment - over;
+    }
+    RegMap[VirtReg] = NumBytesAllocated;
+    NumBytesAllocated += size;
+  }
+  stackOffset = RegMap[VirtReg];
+  PhysReg = getFreeReg(VirtReg);
+
+  // Add move instruction(s)
+  MachineBasicBlock::iterator newI =
+    RegInfo->loadRegOffset2Reg(CurrMBB, I, PhysReg,
+                               RegInfo->getFramePointer(),
+                               stackOffset, regClass->getDataSize());
+
+  // FIXME: increment the frame pointer
+
+  return newI;
+}
+
+MachineBasicBlock::iterator
+RegAllocSimple::saveRegToStack (MachineBasicBlock::iterator I,
+                                unsigned VirtReg, unsigned PhysReg)
+{
+  const TargetRegisterClass* regClass = MF->getRegClass(VirtReg);
+  assert(regClass);
+  assert(RegMap.find(VirtReg) != RegMap.end() &&
+         "Virtual reg has no stack offset mapping!");
+
+  unsigned offset = RegMap[VirtReg];
+  // Add move instruction(s)
+  return RegInfo->storeReg2RegOffset(CurrMBB, I, PhysReg,
+                                     RegInfo->getFramePointer(),
+                                     offset, regClass->getDataSize());
+}
+
+bool RegAllocSimple::runOnMachineFunction(MachineFunction &Fn) {
+  RegMap.clear();
+  unsigned virtualReg, physReg;
+  DEBUG(std::cerr << "Machine Function " << "\n");
+  MF = &Fn;
+  // FIXME: add prolog. we should preserve callee-save registers...
+
+  for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
+       MBB != MBBe; ++MBB)
+  {
+    CurrMBB = &(*MBB);
+
+    // FIXME: if return, special case => into return register
+    //loop over each basic block
+    for (MachineBasicBlock::iterator I = MBB->begin(); I != MBB->end(); ++I)
+    {
+      MachineInstr *MI = *I;
+
+      DEBUG(std::cerr << "instr: ";
+            MI->print(std::cerr, TM));
+
+      // Loop over each instruction:
+      // uses, move from memory into registers
+      for (int i = MI->getNumOperands() - 1; i >= 0; --i) {
+        MachineOperand &op = MI->getOperand(i);
+
+        if (op.getType() == MachineOperand::MO_SignExtendedImmed ||
+            op.getType() == MachineOperand::MO_UnextendedImmed)
+        {
+          DEBUG(std::cerr << "const\n");
+        } else if (op.isVirtualRegister()) {
+          virtualReg = (unsigned) op.getAllocatedRegNum();
+#if 0
+          // FIXME: save register to stack
+          if (op.opIsDef()) {
+            MachineBasicBlock::iterator J = I;
+            saveRegToStack(++J, virtualReg, physReg);
+          }
+#endif
+          DEBUG(std::cerr << "op: " << op << "\n");
+          DEBUG(std::cerr << "\t inst[" << i << "]: ";
+                MI->print(std::cerr, TM));
+          I = moveUseToReg(I, virtualReg, physReg);
+          //MI = *I;
+          bool def = op.opIsDef() || op.opIsDefAndUse();
+          MI->SetMachineOperandReg(i, physReg, def);
+          DEBUG(std::cerr << "virt: " << virtualReg << 
+                ", phys: " << op.getAllocatedRegNum() << "\n");
+        }
+      }
+
+      clearAllRegs();
+    }
+
+  }
+
+  // FIXME: add epilog. we should preserve callee-save registers...
+
+  return false;  // We never modify the LLVM itself.
+}
+
+Pass *createSimpleX86RegisterAllocator(TargetMachine &TM) {
+  return new RegAllocSimple(TM);
+}