CodeGen: Refactor regallocator command line and target selection

[arsenm]

Summary

This will allow targets more flexibility to replace the
register allocator core passes. In a future commit,
AMDGPU will run the core register assignment passes
twice, and will also want to disallow using the
standard -regalloc option.

[aheejin]

lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp

191

Could you clang-format these? clang-format would place these short functions in a single line.

[arsenm]

clang-format

[qcolombet]

include/llvm/CodeGen/TargetPassConfig.h

438

Should the hook says Assignment *and* rewriting?

lib/CodeGen/TargetPassConfig.cpp

900–902

No braces

1114

Where do you draw the line of which pass to pull in that method?
In particular, why pull StackSlotColoring and not MachineCopyPropagation for instance.

[arsenm]

Rename hook, move StackSlotColoring

[qcolombet]

LGTM, one last nitpick below.

lib/CodeGen/TargetPassConfig.cpp

1106

Add a comment on the declaration of addPreRewrite that it may not be honored if the target overloads addRegAssignAndRewriteOptimized or more generally doesn't actually have two distinct passes (e.g., the fast variant wouldn't call into addPreRewrite).

[arsenm]

r356506

include/llvm/CodeGen/TargetPassConfig.h

protected:
   virtual void addPreRegAlloc() { }
 
   /// createTargetRegisterAllocator - Create the register allocator pass for
   /// this target at the current optimization level.
   virtual FunctionPass *createTargetRegisterAllocator(bool Optimized);
 
   /// addFastRegAlloc - Add the minimum set of target-independent passes that
   /// are required for fast register allocation.
-  virtual void addFastRegAlloc(FunctionPass *RegAllocPass);
+  virtual void addFastRegAlloc();
 
   /// addOptimizedRegAlloc - Add passes related to register allocation.
   /// LLVMTargetMachine provides standard regalloc passes for most targets.
-  virtual void addOptimizedRegAlloc(FunctionPass *RegAllocPass);
+  virtual void addOptimizedRegAlloc();
 
   /// addPreRewrite - Add passes to the optimized register allocation pipeline
   /// after register allocation is complete, but before virtual registers are
   /// rewritten to physical registers.
   ///
   /// These passes must preserve VirtRegMap and LiveIntervals, and when running
   /// after RABasic or RAGreedy, they should take advantage of LiveRegMatrix.
   /// When these passes run, VirtRegMap contains legal physreg assignments for
protected:
   /// @p printAfter    if true and adding a machine function pass add an extra
   ///                  machine printer pass afterwards
   /// @p verifyAfter   if true and adding a machine function pass add an extra
   ///                  machine verification pass afterwards.
   void addPass(Pass *P, bool verifyAfter = true, bool printAfter = true);
 
   /// addMachinePasses helper to create the target-selected or overriden
   /// regalloc pass.
-  FunctionPass *createRegAllocPass(bool Optimized);
+  virtual FunctionPass *createRegAllocPass(bool Optimized);
+
+  /// Add core register allocator passes which do the actual register assignment
+  /// and rewriting. \returns true if any passes were added.
+  virtual bool addRegAssignAndRewriteFast();
+  virtual bool addRegAssignAndRewriteOptimized();
 };
 
 } // end namespace llvm
 
 #endif // LLVM_CODEGEN_TARGETPASSCONFIG_H

lib/CodeGen/TargetPassConfig.cpp

if (TM->Options.EnableIPRA)
     addPass(createRegUsageInfoPropPass());
 
   // Run pre-ra passes.
   addPreRegAlloc();
 
   // Run register allocation and passes that are tightly coupled with it,
   // including phi elimination and scheduling.
   if (getOptimizeRegAlloc())
-    addOptimizedRegAlloc(createRegAllocPass(true));
-  else {
-    if (RegAlloc != &useDefaultRegisterAllocator &&
-        RegAlloc != &createFastRegisterAllocator)
-      report_fatal_error("Must use fast (default) register allocator for unoptimized regalloc.");
-    addFastRegAlloc(createRegAllocPass(false));
-  }
+    addOptimizedRegAlloc();
+  else
+    addFastRegAlloc();
 
   // Run post-ra passes.
   addPostRegAlloc();
 
   // Insert prolog/epilog code.  Eliminate abstract frame index references...
   if (getOptLevel() != CodeGenOpt::None) {
     addPass(&PostRAMachineSinkingID);
     addPass(&ShrinkWrapID);
FunctionPass *TargetPassConfig::createRegAllocPass(bool Optimized) {
   RegisterRegAlloc::FunctionPassCtor Ctor = RegisterRegAlloc::getDefault();
   if (Ctor != useDefaultRegisterAllocator)
     return Ctor();
 
   // With no -regalloc= override, ask the target for a regalloc pass.
   return createTargetRegisterAllocator(Optimized);
 }
 
+bool TargetPassConfig::addRegAssignAndRewriteFast() {
+  if (RegAlloc != &useDefaultRegisterAllocator &&
+      RegAlloc != &createFastRegisterAllocator)
+    report_fatal_error("Must use fast (default) register allocator for unoptimized regalloc.");
+
+  addPass(createRegAllocPass(false));
+  return true;
+}
+
+bool TargetPassConfig::addRegAssignAndRewriteOptimized() {
+  // Add the selected register allocation pass.
+  addPass(createRegAllocPass(true));
+
+  // Allow targets to change the register assignments before rewriting.
+  addPreRewrite();
+
+  // Finally rewrite virtual registers.
+  addPass(&VirtRegRewriterID);
+
+  return true;
+}
+
 /// Return true if the default global register allocator is in use and
 /// has not be overriden on the command line with '-regalloc=...'
 bool TargetPassConfig::usingDefaultRegAlloc() const {
   return RegAlloc.getNumOccurrences() == 0;
 }
 
 /// Add the minimum set of target-independent passes that are required for
 /// register allocation. No coalescing or scheduling.
-void TargetPassConfig::addFastRegAlloc(FunctionPass *RegAllocPass) {
+void TargetPassConfig::addFastRegAlloc() {
   addPass(&PHIEliminationID, false);
   addPass(&TwoAddressInstructionPassID, false);
 
-  if (RegAllocPass)
-    addPass(RegAllocPass);
+  addRegAssignAndRewriteFast();
 }
 
 /// Add standard target-independent passes that are tightly coupled with
 /// optimized register allocation, including coalescing, machine instruction
 /// scheduling, and register allocation itself.
-void TargetPassConfig::addOptimizedRegAlloc(FunctionPass *RegAllocPass) {
+void TargetPassConfig::addOptimizedRegAlloc() {
   addPass(&DetectDeadLanesID, false);
 
   addPass(&ProcessImplicitDefsID, false);
 
   // LiveVariables currently requires pure SSA form.
   //
   // FIXME: Once TwoAddressInstruction pass no longer uses kill flags,
   // LiveVariables can be removed completely, and LiveIntervals can be directly
void TargetPassConfig::addOptimizedRegAlloc() {
   // The machine scheduler may accidentally create disconnected components
   // when moving subregister definitions around, avoid this by splitting them to
   // separate vregs before. Splitting can also improve reg. allocation quality.
   addPass(&RenameIndependentSubregsID);
 
   // PreRA instruction scheduling.
   addPass(&MachineSchedulerID);
 
-  if (RegAllocPass) {
-    // Add the selected register allocation pass.
-    addPass(RegAllocPass);
-
-    // Allow targets to change the register assignments before rewriting.
-    addPreRewrite();
-
-    // Finally rewrite virtual registers.
-    addPass(&VirtRegRewriterID);
-
+  if (addRegAssignAndRewriteOptimized()) {
     // Perform stack slot coloring and post-ra machine LICM.
     //
     // FIXME: Re-enable coloring with register when it's capable of adding
     // kill markers.
     addPass(&StackSlotColoringID);
 
     // Copy propagate to forward register uses and try to eliminate COPYs that
     // were not coalesced.

lib/Target/AMDGPU/AMDGPUTargetMachine.cpp

public:
   bool addPreISel() override;
   void addMachineSSAOptimization() override;
   bool addILPOpts() override;
   bool addInstSelector() override;
   bool addIRTranslator() override;
   bool addLegalizeMachineIR() override;
   bool addRegBankSelect() override;
   bool addGlobalInstructionSelect() override;
-  void addFastRegAlloc(FunctionPass *RegAllocPass) override;
-  void addOptimizedRegAlloc(FunctionPass *RegAllocPass) override;
+  void addFastRegAlloc() override;
+  void addOptimizedRegAlloc() override;
   void addPreRegAlloc() override;
   void addPostRegAlloc() override;
   void addPreSched2() override;
   void addPreEmitPass() override;
 };
 
 } // end anonymous namespace
 

 
 void GCNPassConfig::addPreRegAlloc() {
   if (LateCFGStructurize) {
     addPass(createAMDGPUMachineCFGStructurizerPass());
   }
   addPass(createSIWholeQuadModePass());
 }
 
-void GCNPassConfig::addFastRegAlloc(FunctionPass *RegAllocPass) {
+void GCNPassConfig::addFastRegAlloc() {
   // FIXME: We have to disable the verifier here because of PHIElimination +
   // TwoAddressInstructions disabling it.
 
   // This must be run immediately after phi elimination and before
   // TwoAddressInstructions, otherwise the processing of the tied operand of
   // SI_ELSE will introduce a copy of the tied operand source after the else.
   insertPass(&PHIEliminationID, &SILowerControlFlowID, false);
 
   // This must be run after SILowerControlFlow, since it needs to use the
   // machine-level CFG, but before register allocation.
   insertPass(&SILowerControlFlowID, &SIFixWWMLivenessID, false);
 
-  TargetPassConfig::addFastRegAlloc(RegAllocPass);
+  TargetPassConfig::addFastRegAlloc();
 }
 
-void GCNPassConfig::addOptimizedRegAlloc(FunctionPass *RegAllocPass) {
+void GCNPassConfig::addOptimizedRegAlloc() {
   insertPass(&MachineSchedulerID, &SIOptimizeExecMaskingPreRAID);
 
   insertPass(&SIOptimizeExecMaskingPreRAID, &SIFormMemoryClausesID);
 
   // This must be run immediately after phi elimination and before
   // TwoAddressInstructions, otherwise the processing of the tied operand of
   // SI_ELSE will introduce a copy of the tied operand source after the else.
   insertPass(&PHIEliminationID, &SILowerControlFlowID, false);
 
   // This must be run after SILowerControlFlow, since it needs to use the
   // machine-level CFG, but before register allocation.
   insertPass(&SILowerControlFlowID, &SIFixWWMLivenessID, false);
 
-  TargetPassConfig::addOptimizedRegAlloc(RegAllocPass);
+  TargetPassConfig::addOptimizedRegAlloc();
 }
 
 void GCNPassConfig::addPostRegAlloc() {
   addPass(&SIFixVGPRCopiesID);
   if (getOptLevel() > CodeGenOpt::None)
     addPass(&SIOptimizeExecMaskingID);
   TargetPassConfig::addPostRegAlloc();
 }

lib/Target/NVPTX/NVPTXTargetMachine.cpp

public:
 
   void addIRPasses() override;
   bool addInstSelector() override;
   void addPreRegAlloc() override;
   void addPostRegAlloc() override;
   void addMachineSSAOptimization() override;
 
   FunctionPass *createTargetRegisterAllocator(bool) override;
-  void addFastRegAlloc(FunctionPass *RegAllocPass) override;
-  void addOptimizedRegAlloc(FunctionPass *RegAllocPass) override;
+  void addFastRegAlloc() override;
+  void addOptimizedRegAlloc() override;
+
+  bool addRegAssignAndRewriteFast() override {
+    llvm_unreachable("should not be used");
+  }
+
+  bool addRegAssignAndRewriteOptimized() override {
+    llvm_unreachable("should not be used");
+  }
 
 private:
   // If the opt level is aggressive, add GVN; otherwise, add EarlyCSE. This
   // function is only called in opt mode.
   void addEarlyCSEOrGVNPass();
 
   // Add passes that propagate special memory spaces.
   void addAddressSpaceInferencePasses();
if (getOptLevel() != CodeGenOpt::None) {
     addPass(createNVPTXPeephole());
   }
 }
 
 FunctionPass *NVPTXPassConfig::createTargetRegisterAllocator(bool) {
   return nullptr; // No reg alloc
 }
 
-void NVPTXPassConfig::addFastRegAlloc(FunctionPass *RegAllocPass) {
-  assert(!RegAllocPass && "NVPTX uses no regalloc!");
+void NVPTXPassConfig::addFastRegAlloc() {
   addPass(&PHIEliminationID);
   addPass(&TwoAddressInstructionPassID);
 }
 
-void NVPTXPassConfig::addOptimizedRegAlloc(FunctionPass *RegAllocPass) {
-  assert(!RegAllocPass && "NVPTX uses no regalloc!");
-
+void NVPTXPassConfig::addOptimizedRegAlloc() {
   addPass(&ProcessImplicitDefsID);
   addPass(&LiveVariablesID);
   addPass(&MachineLoopInfoID);
   addPass(&PHIEliminationID);
 
   addPass(&TwoAddressInstructionPassID);
   addPass(&RegisterCoalescerID);
 

lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp

public:
 
   FunctionPass *createTargetRegisterAllocator(bool) override;
 
   void addIRPasses() override;
   bool addInstSelector() override;
   void addPostRegAlloc() override;
   bool addGCPasses() override { return false; }
   void addPreEmitPass() override;
+
+  // No reg alloc
+  bool addRegAssignAndRewriteFast() override { return false; }
+
+  // No reg alloc
+  bool addRegAssignAndRewriteOptimized() override { return false; }
 };
 } // end anonymous namespace
 
 TargetTransformInfo
 WebAssemblyTargetMachine::getTargetTransformInfo(const Function &F) {
   return TargetTransformInfo(WebAssemblyTTIImpl(this, F));
 }
 
 TargetPassConfig *
 WebAssemblyTargetMachine::createPassConfig(PassManagerBase &PM) {
   return new WebAssemblyPassConfig(*this, PM);
 }