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Summary: CaptureTracker subclasses might have better dereferenceability information which allows null pointer checks to be no-capturing. The first user will be D59922. Reviewers: sanjoy, hfinkel, aykevl, sstefan1, uenoku, xbolva00 Subscribers: hiraditya, bollu, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D66371 llvm-svn: 369305
104 lines
5.1 KiB
C++
104 lines
5.1 KiB
C++
//===----- llvm/Analysis/CaptureTracking.h - Pointer capture ----*- C++ -*-===//
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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 routines that help determine which pointers are captured.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_CAPTURETRACKING_H
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#define LLVM_ANALYSIS_CAPTURETRACKING_H
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namespace llvm {
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class Value;
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class Use;
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class DataLayout;
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class Instruction;
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class DominatorTree;
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class OrderedBasicBlock;
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/// The default value for MaxUsesToExplore argument. It's relatively small to
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/// keep the cost of analysis reasonable for clients like BasicAliasAnalysis,
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/// where the results can't be cached.
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/// TODO: we should probably introduce a caching CaptureTracking analysis and
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/// use it where possible. The caching version can use much higher limit or
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/// don't have this cap at all.
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unsigned constexpr DefaultMaxUsesToExplore = 20;
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/// PointerMayBeCaptured - Return true if this pointer value may be captured
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/// by the enclosing function (which is required to exist). This routine can
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/// be expensive, so consider caching the results. The boolean ReturnCaptures
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/// specifies whether returning the value (or part of it) from the function
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/// counts as capturing it or not. The boolean StoreCaptures specified
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/// whether storing the value (or part of it) into memory anywhere
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/// automatically counts as capturing it or not.
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/// MaxUsesToExplore specifies how many uses should the analysis explore for
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/// one value before giving up due too "too many uses".
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bool PointerMayBeCaptured(const Value *V,
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bool ReturnCaptures,
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bool StoreCaptures,
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unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
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/// PointerMayBeCapturedBefore - Return true if this pointer value may be
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/// captured by the enclosing function (which is required to exist). If a
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/// DominatorTree is provided, only captures which happen before the given
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/// instruction are considered. This routine can be expensive, so consider
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/// caching the results. The boolean ReturnCaptures specifies whether
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/// returning the value (or part of it) from the function counts as capturing
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/// it or not. The boolean StoreCaptures specified whether storing the value
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/// (or part of it) into memory anywhere automatically counts as capturing it
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/// or not. Captures by the provided instruction are considered if the
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/// final parameter is true. An ordered basic block in \p OBB could be used
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/// to speed up capture-tracker queries.
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/// MaxUsesToExplore specifies how many uses should the analysis explore for
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/// one value before giving up due too "too many uses".
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bool PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures,
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bool StoreCaptures, const Instruction *I,
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const DominatorTree *DT, bool IncludeI = false,
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OrderedBasicBlock *OBB = nullptr,
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unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
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/// This callback is used in conjunction with PointerMayBeCaptured. In
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/// addition to the interface here, you'll need to provide your own getters
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/// to see whether anything was captured.
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struct CaptureTracker {
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virtual ~CaptureTracker();
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/// tooManyUses - The depth of traversal has breached a limit. There may be
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/// capturing instructions that will not be passed into captured().
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virtual void tooManyUses() = 0;
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/// shouldExplore - This is the use of a value derived from the pointer.
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/// To prune the search (ie., assume that none of its users could possibly
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/// capture) return false. To search it, return true.
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///
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/// U->getUser() is always an Instruction.
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virtual bool shouldExplore(const Use *U);
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/// captured - Information about the pointer was captured by the user of
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/// use U. Return true to stop the traversal or false to continue looking
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/// for more capturing instructions.
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virtual bool captured(const Use *U) = 0;
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/// isDereferenceableOrNull - Overload to allow clients with additional
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/// knowledge about pointer dereferenceability to provide it and thereby
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/// avoid conservative responses when a pointer is compared to null.
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virtual bool isDereferenceableOrNull(Value *O, const DataLayout &DL);
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};
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/// PointerMayBeCaptured - Visit the value and the values derived from it and
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/// find values which appear to be capturing the pointer value. This feeds
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/// results into and is controlled by the CaptureTracker object.
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/// MaxUsesToExplore specifies how many uses should the analysis explore for
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/// one value before giving up due too "too many uses".
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void PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
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unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
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} // end namespace llvm
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#endif
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