include/llvm/Analysis/LegacyDivergenceAnalysis.h

   1 //===- llvm/Analysis/LegacyDivergenceAnalysis.h - KernelDivergence Analysis -*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // The kernel divergence analysis is an LLVM pass which can be used to find out
  10 // if a branch instruction in a GPU program (kernel) is divergent or not. It can help
  11 // branch optimizations such as jump threading and loop unswitching to make
  12 // better decisions.
  13 //
  14 //===----------------------------------------------------------------------===//
  15 #ifndef LLVM_ANALYSIS_LEGACY_DIVERGENCE_ANALYSIS_H
  16 #define LLVM_ANALYSIS_LEGACY_DIVERGENCE_ANALYSIS_H
  17
  18 #include "llvm/ADT/DenseSet.h"
  19 #include "llvm/IR/Function.h"
  20 #include "llvm/Pass.h"
  21 #include "llvm/Analysis/DivergenceAnalysis.h"
  22
  23 namespace llvm {
  24 class Value;
  25 class GPUDivergenceAnalysis;
  26 class LegacyDivergenceAnalysis : public FunctionPass {
  27 public:
  28   static char ID;
  29
  30   LegacyDivergenceAnalysis() : FunctionPass(ID) {
  31     initializeLegacyDivergenceAnalysisPass(*PassRegistry::getPassRegistry());
  32   }
  33
  34   void getAnalysisUsage(AnalysisUsage &AU) const override;
  35
  36   bool runOnFunction(Function &F) override;
  37
  38   // Print all divergent branches in the function.
  39   void print(raw_ostream &OS, const Module *) const override;
  40
  41   // Returns true if V is divergent at its definition.
  42   //
  43   // Even if this function returns false, V may still be divergent when used
  44   // in a different basic block.
  45   bool isDivergent(const Value *V) const;
  46
  47   // Returns true if V is uniform/non-divergent.
  48   //
  49   // Even if this function returns true, V may still be divergent when used
  50   // in a different basic block.
  51   bool isUniform(const Value *V) const { return !isDivergent(V); }
  52
  53   // Keep the analysis results uptodate by removing an erased value.
  54   void removeValue(const Value *V) { DivergentValues.erase(V); }
  55
  56 private:
  57   // Whether analysis should be performed by GPUDivergenceAnalysis.
  58   bool shouldUseGPUDivergenceAnalysis(const Function &F) const;
  59
  60   // (optional) handle to new DivergenceAnalysis
  61   std::unique_ptr<GPUDivergenceAnalysis> gpuDA;
  62
  63   // Stores all divergent values.
  64   DenseSet<const Value *> DivergentValues;
  65 };
  66 } // End llvm namespace
  67
  68 #endif //LLVM_ANALYSIS_LEGACY_DIVERGENCE_ANALYSIS_H