Localizer fun

WIP

llvm-svn: 299283

1 files changed, 120 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/Localizer.cpp b/llvm/lib/CodeGen/GlobalISel/Localizer.cpp
new file mode 100644
index 00000000000..e5b1449cdae
--- /dev/null
+++ b/llvm/lib/CodeGen/GlobalISel/Localizer.cpp
@@ -0,0 +1,120 @@
+//===- Localizer.cpp ---------------------- Localize some instrs -*- C++ -*-==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+/// This file implements the Localizer class.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/CodeGen/GlobalISel/Localizer.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "localizer"
+
+using namespace llvm;
+
+char Localizer::ID = 0;
+INITIALIZE_PASS(Localizer, DEBUG_TYPE,
+                "Move/duplicate certain instructions close to their use",
+                false, false);
+
+Localizer::Localizer() : MachineFunctionPass(ID) {
+  initializeLocalizerPass(*PassRegistry::getPassRegistry());
+}
+
+void Localizer::init(MachineFunction &MF) {
+  MRI = &MF.getRegInfo();
+}
+
+bool Localizer::shouldLocalize(const MachineInstr &MI) {
+  switch(MI.getOpcode()) {
+  default:
+    return false;
+  // Constants-like instructions should be close to their users.
+  // We don't want long live-ranges for them.
+  case TargetOpcode::G_CONSTANT:
+  case TargetOpcode::G_FRAME_INDEX:
+    return true;
+  }
+}
+
+bool Localizer::isLocalUse(MachineOperand &MOUse, const MachineInstr &Def, MachineBasicBlock **InsertMBB) {
+  MachineInstr &MIUse = *MOUse.getParent();
+  *InsertMBB = MIUse.getParent();
+  if (MIUse.isPHI())
+    *InsertMBB = MIUse.getOperand(MIUse.getOperandNo(&MOUse) + 1).getMBB();
+  return *InsertMBB == Def.getParent();
+}
+
+bool Localizer::runOnMachineFunction(MachineFunction &MF) {
+  // If the ISel pipeline failed, do not bother running that pass.
+  if (MF.getProperties().hasProperty(
+                                     MachineFunctionProperties::Property::FailedISel))
+    return false;
+
+  DEBUG(dbgs() << "Localize instructions for: " << MF.getName() << '\n');
+
+  init(MF);
+
+  bool Changed = false;
+  // Keep track of the instructions we localized.
+  // We won't need to process them if we see them later in the CFG.
+  SmallPtrSet<MachineInstr *, 16> LocalizedInstrs;
+  DenseMap<std::pair<MachineBasicBlock *, unsigned>, unsigned> MBBWithLocalDef;
+  // TODO: Do bottom up traversal.
+  for (MachineBasicBlock &MBB : MF) {
+    for (MachineInstr &MI : MBB) {
+      if (LocalizedInstrs.count(&MI) || !shouldLocalize(MI))
+        continue;
+      DEBUG(dbgs() << "Should localize: " << MI);
+      assert(MI.getDesc().getNumDefs() == 1 && "More than one definition not supported yet");
+      unsigned Reg = MI.getOperand(0).getReg();
+      // Check if all the users of MI are local.
+      // We are going to invalidation the list of use operands, so we
+      // can't use range iterator.
+      for (auto MOIt =  MRI->use_begin(Reg), MOItEnd = MRI->use_end();
+           MOIt != MOItEnd;) {
+        MachineOperand &MOUse = *MOIt++;
+        // Check if the use is already local.
+        MachineBasicBlock *InsertMBB;
+        DEBUG(MachineInstr &MIUse = *MOUse.getParent();
+              dbgs() << "Checking use: " << MIUse << " #Opd: " << MIUse.getOperandNo(&MOUse) << '\n');
+        if (isLocalUse(MOUse, MI, &InsertMBB))
+          continue;
+        DEBUG(dbgs() << "Fixing non-local use\n");
+        Changed = true;
+        auto MBBAndReg = std::make_pair(InsertMBB, Reg);
+        auto NewVRegIt = MBBWithLocalDef.find(MBBAndReg);
+        if (NewVRegIt == MBBWithLocalDef.end()) {
+          // Create the localized instruction.
+          MachineInstr *LocalizedMI = MF.CloneMachineInstr(&MI);
+          LocalizedInstrs.insert(LocalizedMI);
+          // Move it at the right place.
+          MachineInstr &MIUse = *MOUse.getParent();
+          if (MIUse.getParent() == InsertMBB)
+            InsertMBB->insert(MIUse, LocalizedMI);
+          else
+            InsertMBB->insert(InsertMBB->getFirstNonPHI(), LocalizedMI);
+          
+          // Set a new register for the definition.
+          unsigned NewReg = MRI->createGenericVirtualRegister(MRI->getType(Reg));
+          MRI->setRegClassOrRegBank(NewReg, MRI->getRegClassOrRegBank(Reg));
+          LocalizedMI->getOperand(0).setReg(NewReg);
+          NewVRegIt = MBBWithLocalDef.insert(std::make_pair(MBBAndReg, NewReg)).first;
+          DEBUG(dbgs() << "Inserted: " << *LocalizedMI);
+        }
+        DEBUG(dbgs() << "Update use with: " << PrintReg(NewVRegIt->second) << '\n');
+        // Update the user reg.
+        MOUse.setReg(NewVRegIt->second);
+      }
+    }
+  }
+  return Changed;
+}