path: root/lib/Target/X86/X86FloatingPoint.cpp

//===-- X86FloatingPoint.cpp - Floating point Reg -> Stack converter ------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the pass which converts floating point instructions from
// virtual registers into register stack instructions.  This pass uses live
// variable information to indicate where the FPn registers are used and their
// lifetimes.
//
// This pass is hampered by the lack of decent CFG manipulation routines for
// machine code.  In particular, this wants to be able to split critical edges
// as necessary, traverse the machine basic block CFG in depth-first order, and
// allow there to be multiple machine basic blocks for each LLVM basicblock
// (needed for critical edge splitting).
//
// In particular, this pass currently barfs on critical edges.  Because of this,
// it requires the instruction selector to insert FP_REG_KILL instructions on
// the exits of any basic block that has critical edges going from it, or which
// branch to a critical basic block.
//
// FIXME: this is not implemented yet.  The stackifier pass only works on local
// basic blocks.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "x86-codegen"
#include "X86.h"
#include "X86InstrInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Compiler.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include <algorithm>
#include <set>
using namespace llvm;

STATISTIC(NumFXCH, "Number of fxch instructions inserted");
STATISTIC(NumFP  , "Number of floating point instructions");

namespace {
  struct VISIBILITY_HIDDEN FPS : public MachineFunctionPass {
    static char ID;
    FPS() : MachineFunctionPass((intptr_t)&ID) {}

    virtual bool runOnMachineFunction(MachineFunction &MF);

    virtual const char *getPassName() const { return "X86 FP Stackifier"; }

  private:
    const TargetInstrInfo *TII; // Machine instruction info.
    MachineBasicBlock *MBB;     // Current basic block
    unsigned Stack[8];          // FP<n> Registers in each stack slot...
    unsigned RegMap[8];         // Track which stack slot contains each register
    unsigned StackTop;          // The current top of the FP stack.

    void dumpStack() const {
      cerr << "Stack contents:";
      for (unsigned i = 0; i != StackTop; ++i) {
        cerr << " FP" << Stack[i];
        assert(RegMap[Stack[i]] == i && "Stack[] doesn't match RegMap[]!");
      }
      cerr << "\n";
    }
  private:
    // getSlot - Return the stack slot number a particular register number is
    // in...
    unsigned getSlot(unsigned RegNo) const {
      assert(RegNo < 8 && "Regno out of range!");
      return RegMap[RegNo];
    }

    // getStackEntry - Return the X86::FP<n> register in register ST(i)
    unsigned getStackEntry(unsigned STi) const {
      assert(STi < StackTop && "Access past stack top!");
      return Stack[StackTop-1-STi];
    }

    // getSTReg - Return the X86::ST(i) register which contains the specified
    // FP<RegNo> register
    unsigned getSTReg(unsigned RegNo) const {
      return StackTop - 1 - getSlot(RegNo) + llvm::X86::ST0;
    }

    // pushReg - Push the specified FP<n> register onto the stack
    void pushReg(unsigned Reg) {
      assert(Reg < 8 && "Register number out of range!");
      assert(StackTop < 8 && "Stack overflow!");
      Stack[StackTop] = Reg;
      RegMap[Reg] = StackTop++;
    }

    bool isAtTop(unsigned RegNo) const { return getSlot(RegNo) == StackTop-1; }
    void moveToTop(unsigned RegNo, MachineBasicBlock::iterator &I) {
      if (!isAtTop(RegNo)) {
        unsigned STReg = getSTReg(RegNo);
        unsigned RegOnTop = getStackEntry(0);

        // Swap the slots the regs are in
        std::swap(RegMap[RegNo], RegMap[RegOnTop]);

        // Swap stack slot contents
        assert(RegMap[RegOnTop] < StackTop);
        std::swap(Stack[RegMap[RegOnTop]], Stack[StackTop-1]);

        // Emit an fxch to update the runtime processors version of the state
        BuildMI(*MBB, I, TII->get(X86::XCH_F)).addReg(STReg);
        NumFXCH++;
      }
    }

    void duplicateToTop(unsigned RegNo, unsigned AsReg, MachineInstr *I) {
      unsigned STReg = getSTReg(RegNo);
      pushReg(AsReg);   // New register on top of stack

      BuildMI(*MBB, I, TII->get(X86::LD_Frr)).addReg(STReg);
    }

    // popStackAfter - Pop the current value off of the top of the FP stack
    // after the specified instruction.
    void popStackAfter(MachineBasicBlock::ite