[MIPS GlobalISel] Add pre legalizer combiner pass

[Petar.Avramovic]

Summary

Introduce GlobalISel pre legalizer pass for MIPS.
It will be used to cope with instructions that require
combining before legalization.

[atanasyan]

LGTM

lib/Target/Mips/CMakeLists.txt

add_llvm_target(MipsCodeGen
   MipsFrameLowering.cpp
   MipsLegalizerInfo.cpp
   MipsBranchExpansion.cpp
   MipsMCInstLower.cpp
   MipsMachineFunction.cpp
   MipsModuleISelDAGToDAG.cpp
   MipsOptimizePICCall.cpp
   MipsOs16.cpp
+  MipsPreLegalizerCombiner.cpp
   MipsRegisterBankInfo.cpp
   MipsRegisterInfo.cpp
   MipsSEFrameLowering.cpp
   MipsSEInstrInfo.cpp
   MipsSEISelDAGToDAG.cpp
   MipsSEISelLowering.cpp
   MipsSERegisterInfo.cpp
   MipsSubtarget.cpp

lib/Target/Mips/Mips.h

namespace llvm {
 
   FunctionPass *createMipsModuleISelDagPass();
   FunctionPass *createMipsOptimizePICCallPass();
   FunctionPass *createMipsDelaySlotFillerPass();
   FunctionPass *createMipsBranchExpansion();
   FunctionPass *createMipsConstantIslandPass();
   FunctionPass *createMicroMipsSizeReducePass();
   FunctionPass *createMipsExpandPseudoPass();
+  FunctionPass *createMipsPreLegalizeCombiner();
 
   InstructionSelector *createMipsInstructionSelector(const MipsTargetMachine &,
                                                      MipsSubtarget &,
                                                      MipsRegisterBankInfo &);
 
   void initializeMipsDelaySlotFillerPass(PassRegistry &);
   void initializeMipsBranchExpansionPass(PassRegistry &);
   void initializeMicroMipsSizeReducePass(PassRegistry &);
+  void initializeMipsPreLegalizerCombinerPass(PassRegistry&);
 } // end namespace llvm;
 
 #endif

lib/Target/Mips/MipsPreLegalizerCombiner.cpp

+//=== lib/CodeGen/GlobalISel/MipsPreLegalizerCombiner.cpp --------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass does combining of machine instructions at the generic MI level,
+// before the legalizer.
+//
+//===----------------------------------------------------------------------===//
+
+#include "MipsTargetMachine.h"
+#include "llvm/CodeGen/GlobalISel/Combiner.h"
+#include "llvm/CodeGen/GlobalISel/CombinerInfo.h"
+#include "llvm/CodeGen/GlobalISel/MIPatternMatch.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+
+#define DEBUG_TYPE "mips-prelegalizer-combiner"
+
+using namespace llvm;
+
+namespace {
+class MipsPreLegalizerCombinerInfo : public CombinerInfo {
+public:
+  MipsPreLegalizerCombinerInfo()
+      : CombinerInfo(/*AllowIllegalOps*/ true, /*ShouldLegalizeIllegal*/ false,
+                     /*LegalizerInfo*/ nullptr) {}
+  virtual bool combine(GISelChangeObserver &Observer, MachineInstr &MI,
+                       MachineIRBuilder &B) const override;
+};
+
+bool MipsPreLegalizerCombinerInfo::combine(GISelChangeObserver &Observer,
+                                           MachineInstr &MI,
+                                           MachineIRBuilder &B) const {
+  return false;
+}
+
+// Pass boilerplate
+// ================
+
+class MipsPreLegalizerCombiner : public MachineFunctionPass {
+public:
+  static char ID;
+
+  MipsPreLegalizerCombiner();
+
+  StringRef getPassName() const override { return "MipsPreLegalizerCombiner"; }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+};
+} // end anonymous namespace
+
+void MipsPreLegalizerCombiner::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequired<TargetPassConfig>();
+  AU.setPreservesCFG();
+  getSelectionDAGFallbackAnalysisUsage(AU);
+  MachineFunctionPass::getAnalysisUsage(AU);
+}
+
+MipsPreLegalizerCombiner::MipsPreLegalizerCombiner() : MachineFunctionPass(ID) {
+  initializeMipsPreLegalizerCombinerPass(*PassRegistry::getPassRegistry());
+}
+
+bool MipsPreLegalizerCombiner::runOnMachineFunction(MachineFunction &MF) {
+  if (MF.getProperties().hasProperty(
+          MachineFunctionProperties::Property::FailedISel))
+    return false;
+  auto *TPC = &getAnalysis<TargetPassConfig>();
+  MipsPreLegalizerCombinerInfo PCInfo;
+  Combiner C(PCInfo, TPC);
+  return C.combineMachineInstrs(MF);
+}
+
+char MipsPreLegalizerCombiner::ID = 0;
+INITIALIZE_PASS_BEGIN(MipsPreLegalizerCombiner, DEBUG_TYPE,
+                      "Combine Mips machine instrs before legalization", false,
+                      false)
+INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
+INITIALIZE_PASS_END(MipsPreLegalizerCombiner, DEBUG_TYPE,
+                    "Combine Mips machine instrs before legalization", false,
+                    false)
+
+namespace llvm {
+FunctionPass *createMipsPreLegalizeCombiner() {
+  return new MipsPreLegalizerCombiner();
+}
+} // end namespace llvm

lib/Target/Mips/MipsTargetMachine.cpp

extern "C" void LLVMInitializeMipsTarget() {
   RegisterTargetMachine<MipsebTargetMachine> A(getTheMips64Target());
   RegisterTargetMachine<MipselTargetMachine> B(getTheMips64elTarget());
 
   PassRegistry *PR = PassRegistry::getPassRegistry();
   initializeGlobalISel(*PR);
   initializeMipsDelaySlotFillerPass(*PR);
   initializeMipsBranchExpansionPass(*PR);
   initializeMicroMipsSizeReducePass(*PR);
+  initializeMipsPreLegalizerCombinerPass(*PR);
 }
 
 static std::string computeDataLayout(const Triple &TT, StringRef CPU,
                                      const TargetOptions &Options,
                                      bool isLittle) {
   std::string Ret;
   MipsABIInfo ABI = MipsABIInfo::computeTargetABI(TT, CPU, Options.MCOptions);
 
const MipsSubtarget &getMipsSubtarget() const {
     return *getMipsTargetMachine().getSubtargetImpl();
   }
 
   void addIRPasses() override;
   bool addInstSelector() override;
   void addPreEmitPass() override;
   void addPreRegAlloc() override;
   bool addIRTranslator() override;
+  void addPreLegalizeMachineIR() override;
   bool addLegalizeMachineIR() override;
   bool addRegBankSelect() override;
   bool addGlobalInstructionSelect() override;
 };
 
 } // end anonymous namespace
 
 TargetPassConfig *MipsTargetMachine::createPassConfig(PassManagerBase &PM) {
void MipsPassConfig::addPreEmitPass() {
   addPass(createMipsConstantIslandPass());
 }
 
 bool MipsPassConfig::addIRTranslator() {
   addPass(new IRTranslator());
   return false;
 }
 
+void MipsPassConfig::addPreLegalizeMachineIR() {
+  addPass(createMipsPreLegalizeCombiner());
+}
+
 bool MipsPassConfig::addLegalizeMachineIR() {
   addPass(new Legalizer());
   return false;
 }
 
 bool MipsPassConfig::addRegBankSelect() {
   addPass(new RegBankSelect());
   return false;
 }
 
 bool MipsPassConfig::addGlobalInstructionSelect() {
   addPass(new InstructionSelect());
   return false;
 }

test/CodeGen/Mips/GlobalISel/mips-prelegalizer-combiner/tryCombine.mir

+# RUN: llc -O0 -mtriple=mipsel-linux-gnu -run-pass=mips-prelegalizer-combiner -verify-machineinstrs -debug %s -o - 2>&1 | FileCheck %s -check-prefixes=MIPS32
+--- |
+
+  define void @f() {entry: ret void}
+
+...
+---
+# Check that we report attempts to combine each instruction from the input
+# since none of them gets changed in this test.
+
+# MIPS32-LABEL: Generic MI Combiner for: f
+# MIPS32: Try combining %0:_(s32) = COPY $a0
+# MIPS32: Try combining %1:_(s32) = COPY $a1
+# MIPS32: Try combining %2:_(s32) = G_ADD %1:_, %0:_
+# MIPS32: Try combining $v0 = COPY %2:_(s32)
+# MIPS32: Try combining RetRA implicit $v0
+name:            f
+alignment:       2
+tracksRegLiveness: true
+body:             |
+  bb.1.entry:
+    liveins: $a0, $a1
+
+    ; MIPS32-LABEL: name: f
+    ; MIPS32: liveins: $a0, $a1
+    ; MIPS32: [[COPY:%[0-9]+]]:_(s32) = COPY $a0
+    ; MIPS32: [[COPY1:%[0-9]+]]:_(s32) = COPY $a1
+    ; MIPS32: [[ADD:%[0-9]+]]:_(s32) = G_ADD [[COPY1]], [[COPY]]
+    ; MIPS32: $v0 = COPY [[ADD]](s32)
+    ; MIPS32: RetRA implicit $v0
+    %0:_(s32) = COPY $a0
+    %1:_(s32) = COPY $a1
+    %2:_(s32) = G_ADD %1, %0
+    $v0 = COPY %2(s32)
+    RetRA implicit $v0
+
+...