Add TwoAddressInstructionPass to handle instructions that have two or

more operands and the two first operands are constrained to be the
same. The pass takes an instruction of the form:

        a = b op c

and transforms it into:

        a = b
        a = a op c

and also preserves live variables.

llvm-svn: 10512

1 files changed, 149 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp b/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
new file mode 100644
index 00000000000..0716ca92a3c
--- /dev/null
+++ b/llvm/lib/CodeGen/TwoAddressInstructionPass.cpp
@@ -0,0 +1,149 @@
+//===-- TwoAddressInstructionPass.cpp - Two-Address instruction pass ------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the LiveInterval analysis pass which is used
+// by the Linear Scan Register allocator. This pass linearizes the
+// basic blocks of the function in DFS order and uses the
+// LiveVariables pass to conservatively compute live intervals for
+// each virtual and physical register.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "twoaddrinstr"
+#include "llvm/CodeGen/TwoAddressInstructionPass.h"
+#include "llvm/Function.h"
+#include "llvm/CodeGen/LiveVariables.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/SSARegMap.h"
+#include "llvm/Target/MRegisterInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Target/TargetRegInfo.h"
+#include "Support/Debug.h"
+#include "Support/Statistic.h"
+#include "Support/STLExtras.h"
+#include <iostream>
+
+using namespace llvm;
+
+namespace {
+    RegisterAnalysis<TwoAddressInstructionPass> X(
+        "twoaddressinstruction", "Two-Address instruction pass");
+
+    Statistic<> numTwoAddressInstrs("twoaddressinstruction",
+                                    "Number of two-address instructions");
+    Statistic<> numInstrsAdded("twoaddressinstruction",
+                               "Number of instructions added");
+};
+
+void TwoAddressInstructionPass::getAnalysisUsage(AnalysisUsage &AU) const
+{
+    AU.addPreserved<LiveVariables>();
+    AU.addRequired<LiveVariables>();
+    AU.addPreservedID(PHIEliminationID);
+    AU.addRequiredID(PHIEliminationID);
+    MachineFunctionPass::getAnalysisUsage(AU);
+}
+
+/// runOnMachineFunction - Reduce two-address instructions to two
+/// operands
+///
+bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &fn) {
+    DEBUG(std::cerr << "Machine Function\n");
+    mf_ = &fn;
+    tm_ = &fn.getTarget();
+    mri_ = tm_->getRegisterInfo();
+    lv_ = &getAnalysis<LiveVariables>();
+
+    const TargetInstrInfo& tii = tm_->getInstrInfo();
+
+    for (MachineFunction::iterator mbbi = mf_->begin(), mbbe = mf_->end();
+         mbbi != mbbe; ++mbbi) {
+        for (MachineBasicBlock::iterator mii = mbbi->begin();
+             mii != mbbi->end(); ++mii) {
+            MachineInstr* mi = *mii;
+
+            unsigned opcode = mi->getOpcode();
+            // ignore if it is not a two-address instruction
+            if (!tii.isTwoAddrInstr(opcode))
+                continue;
+
+            ++numTwoAddressInstrs;
+
+            DEBUG(std::cerr << "\tinstruction: "; mi->print(std::cerr, *tm_));
+
+            // we have nothing to do if the two operands are the same
+            if (mi->getOperand(0).getAllocatedRegNum() ==
+                mi->getOperand(1).getAllocatedRegNum())
+                continue;
+
+            assert(mi->getOperand(1).isRegister() &&
+                   mi->getOperand(1).getAllocatedRegNum() &&
+                   mi->getOperand(1).isUse() &&
+                   "two address instruction invalid");
+
+            // rewrite:
+            //     a = b op c
+            // to:
+            //     a = b
+            //     a = a op c
+            unsigned regA = mi->getOperand(0).getAllocatedRegNum();
+            unsigned regB = mi->getOperand(1).getAllocatedRegNum();
+            bool regAisPhysical = regA < MRegisterInfo::FirstVirtualRegister;
+            bool regBisPhysical = regB < MRegisterInfo::FirstVirtualRegister;
+
+            const TargetRegisterClass* rc = regAisPhysical ?
+                mri_->getRegClass(regA) :
+                mf_->getSSARegMap()->getRegClass(regA);
+
+            numInstrsAdded += mri_->copyRegToReg(*mbbi, mii, regA, regB, rc);
+
+            MachineInstr* prevMi = *(mii - 1);
+            DEBUG(std::cerr << "\t\tadded instruction: ";
+                  prevMi->print(std::cerr, *tm_));
+
+            // update live variables for regA
+            if (regAisPhysical) {
+                lv_->HandlePhysRegDef(regA, prevMi);
+            }
+            else {
+                LiveVariables::VarInfo& varInfo = lv_->getVarInfo(regA);
+                varInfo.DefInst = prevMi;
+            }
+
+            // update live variables for regB
+            if (regBisPhysical) {
+                lv_->HandlePhysRegUse(regB, prevMi);
+            }
+            else {
+                if (lv_->removeVirtualRegisterKilled(regB, &*mbbi, mi))
+                    lv_->addVirtualRegisterKilled(regB, &*mbbi, prevMi);
+
+                if (lv_->removeVirtualRegisterDead(regB, &*mbbi, mi))
+                    lv_->addVirtualRegisterDead(regB, &*mbbi, prevMi);
+            }
+
+            // replace all occurences of regB with regA
+            for (unsigned i = 1; i < mi->getNumOperands(); ++i) {
+                if (mi->getOperand(i).isRegister() &&
+                    mi->getOperand(i).getReg() == regB)
+                    mi->SetMachineOperandReg(i, regA);
+            }
+            DEBUG(std::cerr << "\t\tmodified original to: ";
+                  mi->print(std::cerr, *tm_));
+            assert(mi->getOperand(0).getAllocatedRegNum() ==
+                   mi->getOperand(1).getAllocatedRegNum());
+        }
+    }
+
+    return numInstrsAdded != 0;
+}