[DA][TTI][AMDGPU] Add option to select GPUDA with TTI

[kerbowa]

Summary

Enable the new diveregence analysis by default for AMDGPU.

[rampitec]

llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp

72

Do you need this new option if there is -use-gpu-divergence-analysis?

[kerbowa]

llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp

72

The new cl option disables the new DA for AMDGPU. You can't do that with -use-gpu-divergence-analysis.

[rampitec]

LGTM

[thakis]

Tests on Windows have been broken for over 12h now: http://lab.llvm.org:8011/builders/clang-x64-windows-msvc/builds/13808 I've reverted this for now in cd470717d15854fb778f2c96667ba36672af6cf5 . Sorry about the toil!

llvm/include/llvm/Analysis/LegacyDivergenceAnalysis.h

public:
   // divergent.
   bool isUniformUse(const Use *U) const { return !isDivergentUse(U); }
 
   // Keep the analysis results uptodate by removing an erased value.
   void removeValue(const Value *V) { DivergentValues.erase(V); }
 
 private:
   // Whether analysis should be performed by GPUDivergenceAnalysis.
-  bool shouldUseGPUDivergenceAnalysis(const Function &F) const;
+  bool shouldUseGPUDivergenceAnalysis(const Function &F,
+                                      const TargetTransformInfo &TTI) const;
 
   // (optional) handle to new DivergenceAnalysis
   std::unique_ptr<GPUDivergenceAnalysis> gpuDA;
 
   // Stores all divergent values.
   DenseSet<const Value *> DivergentValues;
 
   // Stores divergent uses of possibly uniform values.
   DenseSet<const Use *> DivergentUses;
 };
 } // End llvm namespace
 
 #endif //LLVM_ANALYSIS_LEGACY_DIVERGENCE_ANALYSIS_H

llvm/include/llvm/Analysis/TargetTransformInfo.h

public:
 
   /// Return true if branch divergence exists.
   ///
   /// Branch divergence has a significantly negative impact on GPU performance
   /// when threads in the same wavefront take different paths due to conditional
   /// branches.
   bool hasBranchDivergence() const;
 
+  /// Return true if the target prefers to use GPU divergence analysis to
+  /// replace the legacy version.
+  bool useGPUDivergenceAnalysis() const;
+
   /// Returns whether V is a source of divergence.
   ///
   /// This function provides the target-dependent information for
   /// the target-independent LegacyDivergenceAnalysis. LegacyDivergenceAnalysis first
   /// builds the dependency graph, and then runs the reachability algorithm
   /// starting with the sources of divergence.
   bool isSourceOfDivergence(const Value *V) const;
 
public:
   virtual int getMemcpyCost(const Instruction *I) = 0;
   virtual unsigned getEstimatedNumberOfCaseClusters(const SwitchInst &SI,
                                                     unsigned &JTSize,
                                                     ProfileSummaryInfo *PSI,
                                                     BlockFrequencyInfo *BFI) = 0;
   virtual int
   getUserCost(const User *U, ArrayRef<const Value *> Operands) = 0;
   virtual bool hasBranchDivergence() = 0;
+  virtual bool useGPUDivergenceAnalysis() = 0;
   virtual bool isSourceOfDivergence(const Value *V) = 0;
   virtual bool isAlwaysUniform(const Value *V) = 0;
   virtual unsigned getFlatAddressSpace() = 0;
   virtual bool collectFlatAddressOperands(SmallVectorImpl<int> &OpIndexes,
                                           Intrinsic::ID IID) const = 0;
   virtual bool rewriteIntrinsicWithAddressSpace(
     IntrinsicInst *II, Value *OldV, Value *NewV) const = 0;
   virtual bool isLoweredToCall(const Function *F) = 0;
public:
   }
   int getMemcpyCost(const Instruction *I) override {
     return Impl.getMemcpyCost(I);
   }
   int getUserCost(const User *U, ArrayRef<const Value *> Operands) override {
     return Impl.getUserCost(U, Operands);
   }
   bool hasBranchDivergence() override { return Impl.hasBranchDivergence(); }
+  bool useGPUDivergenceAnalysis() override { return Impl.useGPUDivergenceAnalysis(); }
   bool isSourceOfDivergence(const Value *V) override {
     return Impl.isSourceOfDivergence(V);
   }
 
   bool isAlwaysUniform(const Value *V) override {
     return Impl.isAlwaysUniform(V);
   }
 

llvm/include/llvm/Analysis/TargetTransformInfoImpl.h

public:
   int getInlinerVectorBonusPercent() { return 150; }
 
   unsigned getMemcpyCost(const Instruction *I) {
     return TTI::TCC_Expensive;
   }
 
   bool hasBranchDivergence() { return false; }
 
+  bool useGPUDivergenceAnalysis() { return false; }
+
   bool isSourceOfDivergence(const Value *V) { return false; }
 
   bool isAlwaysUniform(const Value *V) { return false; }
 
   unsigned getFlatAddressSpace () {
     return -1;
   }
 

llvm/include/llvm/CodeGen/BasicTTIImpl.h

bool allowsMisalignedMemoryAccesses(LLVMContext &Context, unsigned BitWidth,
                                       bool *Fast) const {
     EVT E = EVT::getIntegerVT(Context, BitWidth);
     return getTLI()->allowsMisalignedMemoryAccesses(
         E, AddressSpace, Alignment, MachineMemOperand::MONone, Fast);
   }
 
   bool hasBranchDivergence() { return false; }
 
+  bool useGPUDivergenceAnalysis() { return false; }
+
   bool isSourceOfDivergence(const Value *V) { return false; }
 
   bool isAlwaysUniform(const Value *V) { return false; }
 
   unsigned getFlatAddressSpace() {
     // Return an invalid address space.
     return -1;
   }

llvm/lib/Analysis/LegacyDivergenceAnalysis.cpp

 
 FunctionPass *llvm::createLegacyDivergenceAnalysisPass() {
   return new LegacyDivergenceAnalysis();
 }
 
 void LegacyDivergenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addRequired<DominatorTreeWrapperPass>();
   AU.addRequired<PostDominatorTreeWrapperPass>();
-  if (UseGPUDA)
-    AU.addRequired<LoopInfoWrapperPass>();
   AU.setPreservesAll();
 }
 
 bool LegacyDivergenceAnalysis::shouldUseGPUDivergenceAnalysis(
-    const Function &F) const {
-  if (!UseGPUDA)
+    const Function &F, const TargetTransformInfo &TTI) const {
+  if (!(UseGPUDA || TTI.useGPUDivergenceAnalysis()))
     return false;
 
   // GPUDivergenceAnalysis requires a reducible CFG.
   auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
   using RPOTraversal = ReversePostOrderTraversal<const Function *>;
   RPOTraversal FuncRPOT(&F);
   return !containsIrreducibleCFG<const BasicBlock *, const RPOTraversal,
                                  const LoopInfo>(FuncRPOT, LI);
bool LegacyDivergenceAnalysis::runOnFunction(Function &F) {
 
   DivergentValues.clear();
   DivergentUses.clear();
   gpuDA = nullptr;
 
   auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
   auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
 
-  if (shouldUseGPUDivergenceAnalysis(F)) {
+  if (shouldUseGPUDivergenceAnalysis(F, TTI)) {
     // run the new GPU divergence analysis
     auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
     gpuDA = std::make_unique<GPUDivergenceAnalysis>(F, DT, PDT, LI, TTI);
 
   } else {
     // run LLVM's existing DivergenceAnalysis
     DivergencePropagator DP(F, TTI, DT, PDT, DivergentValues, DivergentUses);
     DP.populateWithSourcesOfDivergence();

llvm/lib/Analysis/TargetTransformInfo.cpp

int TargetTransformInfo::getUserCost(const User *U,
   assert(Cost >= 0 && "TTI should not produce negative costs!");
   return Cost;
 }
 
 bool TargetTransformInfo::hasBranchDivergence() const {
   return TTIImpl->hasBranchDivergence();
 }
 
+bool TargetTransformInfo::useGPUDivergenceAnalysis() const {
+  return TTIImpl->useGPUDivergenceAnalysis();
+}
+
 bool TargetTransformInfo::isSourceOfDivergence(const Value *V) const {
   return TTIImpl->isSourceOfDivergence(V);
 }
 
 bool llvm::TargetTransformInfo::isAlwaysUniform(const Value *V) const {
   return TTIImpl->isAlwaysUniform(V);
 }
 

llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.h

explicit GCNTTIImpl(const AMDGPUTargetMachine *TM, const Function &F)
     : BaseT(TM, F.getParent()->getDataLayout()),
       ST(static_cast<const GCNSubtarget*>(TM->getSubtargetImpl(F))),
       TLI(ST->getTargetLowering()),
       CommonTTI(TM, F),
       IsGraphicsShader(AMDGPU::isShader(F.getCallingConv())),
       HasFP32Denormals(ST->hasFP32Denormals(F)) { }
 
   bool hasBranchDivergence() { return true; }
+  bool useGPUDivergenceAnalysis() const;
 
   void getUnrollingPreferences(Loop *L, ScalarEvolution &SE,
                                TTI::UnrollingPreferences &UP);
 
   TTI::PopcntSupportKind getPopcntSupport(unsigned TyWidth) {
     assert(isPowerOf2_32(TyWidth) && "Ty width must be power of 2");
     return TTI::PSK_FastHardware;
   }

llvm/lib/Target/AMDGPU/AMDGPUTargetTransformInfo.cpp

static cl::opt<unsigned> UnrollThresholdLocal(
   cl::desc("Unroll threshold for AMDGPU if local memory used in a loop"),
   cl::init(1000), cl::Hidden);
 
 static cl::opt<unsigned> UnrollThresholdIf(
   "amdgpu-unroll-threshold-if",
   cl::desc("Unroll threshold increment for AMDGPU for each if statement inside loop"),
   cl::init(150), cl::Hidden);
 
+static cl::opt<bool> UseLegacyDA(
+  "amdgpu-use-legacy-divergence-analysis",
+  cl::desc("Enable legacy divergence analysis for AMDGPU"),
+  cl::init(false), cl::Hidden);
+
 static bool dependsOnLocalPhi(const Loop *L, const Value *Cond,
                               unsigned Depth = 0) {
   const Instruction *I = dyn_cast<Instruction>(Cond);
   if (!I)
     return false;
 
   for (const Value *V : I->operand_values()) {
     if (!L->contains(I))
case CallingConv::AMDGPU_CS:
     return F->getAttributes().hasParamAttribute(A->getArgNo(), Attribute::InReg) ||
            F->getAttributes().hasParamAttribute(A->getArgNo(), Attribute::ByVal);
   default:
     // TODO: Should calls support inreg for SGPR inputs?
     return false;
   }
 }
 
+/// \returns true if the new GPU divergence analysis is enabled.
+bool GCNTTIImpl::useGPUDivergenceAnalysis() const {
+  return !UseLegacyDA;
+}
+
 /// \returns true if the result of the value could potentially be
 /// different across workitems in a wavefront.
 bool GCNTTIImpl::isSourceOfDivergence(const Value *V) const {
   if (const Argument *A = dyn_cast<Argument>(V))
     return !isArgPassedInSGPR(A);
 
   // Loads from the private and flat address spaces are divergent, because
   // threads can execute the load instruction with the same inputs and get