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      1 //===-- AMDGPUTargetTransformInfo.cpp - AMDGPU specific TTI pass ---------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // \file
     11 // This file implements a TargetTransformInfo analysis pass specific to the
     12 // AMDGPU target machine. It uses the target's detailed information to provide
     13 // more precise answers to certain TTI queries, while letting the target
     14 // independent and default TTI implementations handle the rest.
     15 //
     16 //===----------------------------------------------------------------------===//
     17 
     18 #include "AMDGPU.h"
     19 #include "AMDGPUTargetMachine.h"
     20 #include "llvm/Analysis/LoopInfo.h"
     21 #include "llvm/Analysis/TargetTransformInfo.h"
     22 #include "llvm/Analysis/ValueTracking.h"
     23 #include "llvm/Support/Debug.h"
     24 #include "llvm/Target/CostTable.h"
     25 #include "llvm/Target/TargetLowering.h"
     26 using namespace llvm;
     27 
     28 #define DEBUG_TYPE "AMDGPUtti"
     29 
     30 // Declare the pass initialization routine locally as target-specific passes
     31 // don't have a target-wide initialization entry point, and so we rely on the
     32 // pass constructor initialization.
     33 namespace llvm {
     34 void initializeAMDGPUTTIPass(PassRegistry &);
     35 }
     36 
     37 namespace {
     38 
     39 class AMDGPUTTI final : public ImmutablePass, public TargetTransformInfo {
     40   const AMDGPUTargetMachine *TM;
     41   const AMDGPUSubtarget *ST;
     42   const AMDGPUTargetLowering *TLI;
     43 
     44   /// Estimate the overhead of scalarizing an instruction. Insert and Extract
     45   /// are set if the result needs to be inserted and/or extracted from vectors.
     46   unsigned getScalarizationOverhead(Type *Ty, bool Insert, bool Extract) const;
     47 
     48 public:
     49   AMDGPUTTI() : ImmutablePass(ID), TM(nullptr), ST(nullptr), TLI(nullptr) {
     50     llvm_unreachable("This pass cannot be directly constructed");
     51   }
     52 
     53   AMDGPUTTI(const AMDGPUTargetMachine *TM)
     54       : ImmutablePass(ID), TM(TM), ST(TM->getSubtargetImpl()),
     55         TLI(TM->getTargetLowering()) {
     56     initializeAMDGPUTTIPass(*PassRegistry::getPassRegistry());
     57   }
     58 
     59   void initializePass() override { pushTTIStack(this); }
     60 
     61   void getAnalysisUsage(AnalysisUsage &AU) const override {
     62     TargetTransformInfo::getAnalysisUsage(AU);
     63   }
     64 
     65   /// Pass identification.
     66   static char ID;
     67 
     68   /// Provide necessary pointer adjustments for the two base classes.
     69   void *getAdjustedAnalysisPointer(const void *ID) override {
     70     if (ID == &TargetTransformInfo::ID)
     71       return (TargetTransformInfo *)this;
     72     return this;
     73   }
     74 
     75   bool hasBranchDivergence() const override;
     76 
     77   void getUnrollingPreferences(Loop *L,
     78                                UnrollingPreferences &UP) const override;
     79 
     80   /// @}
     81 };
     82 
     83 } // end anonymous namespace
     84 
     85 INITIALIZE_AG_PASS(AMDGPUTTI, TargetTransformInfo, "AMDGPUtti",
     86                    "AMDGPU Target Transform Info", true, true, false)
     87 char AMDGPUTTI::ID = 0;
     88 
     89 ImmutablePass *
     90 llvm::createAMDGPUTargetTransformInfoPass(const AMDGPUTargetMachine *TM) {
     91   return new AMDGPUTTI(TM);
     92 }
     93 
     94 bool AMDGPUTTI::hasBranchDivergence() const { return true; }
     95 
     96 void AMDGPUTTI::getUnrollingPreferences(Loop *L,
     97                                         UnrollingPreferences &UP) const {
     98   for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
     99                                                   BI != BE; ++BI) {
    100     BasicBlock *BB = *BI;
    101     for (BasicBlock::const_iterator I = BB->begin(), E = BB->end();
    102                                                       I != E; ++I) {
    103       const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I);
    104       if (!GEP)
    105         continue;
    106       const Value *Ptr = GEP->getPointerOperand();
    107       const AllocaInst *Alloca = dyn_cast<AllocaInst>(GetUnderlyingObject(Ptr));
    108       if (Alloca) {
    109         // We want to do whatever we can to limit the number of alloca
    110         // instructions that make it through to the code generator.  allocas
    111         // require us to use indirect addressing, which is slow and prone to
    112         // compiler bugs.  If this loop does an address calculation on an
    113         // alloca ptr, then we want to use a higher than normal loop unroll
    114         // threshold. This will give SROA a better chance to eliminate these
    115         // allocas.
    116         //
    117         // Don't use the maximum allowed value here as it will make some
    118         // programs way too big.
    119         UP.Threshold = 500;
    120       }
    121     }
    122   }
    123 }
    124