1 //===- llvm/Analysis/DivergenceAnalysis.h - Divergence Analysis -*- C++ -*-===//
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 // The divergence analysis is an LLVM pass which can be used to find out
11 // if a branch instruction in a GPU program is divergent or not. It can help
12 // branch optimizations such as jump threading and loop unswitching to make
13 // better decisions.
14 //
15 //===----------------------------------------------------------------------===//
16 
17 #include "llvm/ADT/DenseSet.h"
18 #include "llvm/IR/Function.h"
19 #include "llvm/Pass.h"
20 
21 namespace llvm {
22 class Value;
23 class DivergenceAnalysis : public FunctionPass {
24 public:
25   static char ID;
26 
DivergenceAnalysis()27   DivergenceAnalysis() : FunctionPass(ID) {
28     initializeDivergenceAnalysisPass(*PassRegistry::getPassRegistry());
29   }
30 
31   void getAnalysisUsage(AnalysisUsage &AU) const override;
32 
33   bool runOnFunction(Function &F) override;
34 
35   // Print all divergent branches in the function.
36   void print(raw_ostream &OS, const Module *) const override;
37 
38   // Returns true if V is divergent.
isDivergent(const Value * V)39   bool isDivergent(const Value *V) const { return DivergentValues.count(V); }
40 
41   // Returns true if V is uniform/non-divergent.
isUniform(const Value * V)42   bool isUniform(const Value *V) const { return !isDivergent(V); }
43 
44 private:
45   // Stores all divergent values.
46   DenseSet<const Value *> DivergentValues;
47 };
48 } // End llvm namespace
49