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