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Diffstat (limited to 'lib/Transforms/Instrumentation/ValueProfileCollector.h')
-rw-r--r-- | lib/Transforms/Instrumentation/ValueProfileCollector.h | 79 |
1 files changed, 79 insertions, 0 deletions
diff --git a/lib/Transforms/Instrumentation/ValueProfileCollector.h b/lib/Transforms/Instrumentation/ValueProfileCollector.h new file mode 100644 index 000000000000..ff883c8d0c77 --- /dev/null +++ b/lib/Transforms/Instrumentation/ValueProfileCollector.h @@ -0,0 +1,79 @@ +//===- ValueProfileCollector.h - determine what to value profile ----------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This file contains a utility class, ValueProfileCollector, that is used to +// determine what kind of llvm::Value's are worth value-profiling, at which +// point in the program, and which instruction holds the Value Profile metadata. +// Currently, the only users of this utility is the PGOInstrumentation[Gen|Use] +// passes. +//===----------------------------------------------------------------------===// + +#ifndef LLVM_ANALYSIS_PROFILE_GEN_ANALYSIS_H +#define LLVM_ANALYSIS_PROFILE_GEN_ANALYSIS_H + +#include "llvm/IR/Function.h" +#include "llvm/IR/PassManager.h" +#include "llvm/Pass.h" +#include "llvm/ProfileData/InstrProf.h" + +namespace llvm { + +/// Utility analysis that determines what values are worth profiling. +/// The actual logic is inside the ValueProfileCollectorImpl, whose job is to +/// populate the Candidates vector. +/// +/// Value profiling an expression means to track the values that this expression +/// takes at runtime and the frequency of each value. +/// It is important to distinguish between two sets of value profiles for a +/// particular expression: +/// 1) The set of values at the point of evaluation. +/// 2) The set of values at the point of use. +/// In some cases, the two sets are identical, but it's not unusual for the two +/// to differ. +/// +/// To elaborate more, consider this C code, and focus on the expression `nn`: +/// void foo(int nn, bool b) { +/// if (b) memcpy(x, y, nn); +/// } +/// The point of evaluation can be as early as the start of the function, and +/// let's say the value profile for `nn` is: +/// total=100; (value,freq) set = {(8,10), (32,50)} +/// The point of use is right before we call memcpy, and since we execute the +/// memcpy conditionally, the value profile of `nn` can be: +/// total=15; (value,freq) set = {(8,10), (4,5)} +/// +/// For this reason, a plugin is responsible for computing the insertion point +/// for each value to be profiled. The `CandidateInfo` structure encapsulates +/// all the information needed for each value profile site. +class ValueProfileCollector { +public: + struct CandidateInfo { + Value *V; // The value to profile. + Instruction *InsertPt; // Insert the VP lib call before this instr. + Instruction *AnnotatedInst; // Where metadata is attached. + }; + + ValueProfileCollector(Function &Fn); + ValueProfileCollector(ValueProfileCollector &&) = delete; + ValueProfileCollector &operator=(ValueProfileCollector &&) = delete; + + ValueProfileCollector(const ValueProfileCollector &) = delete; + ValueProfileCollector &operator=(const ValueProfileCollector &) = delete; + ~ValueProfileCollector(); + + /// returns a list of value profiling candidates of the given kind + std::vector<CandidateInfo> get(InstrProfValueKind Kind) const; + +private: + class ValueProfileCollectorImpl; + std::unique_ptr<ValueProfileCollectorImpl> PImpl; +}; + +} // namespace llvm + +#endif |