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5a81e14385
This patch introduces a new mechanism that allows IR modules to co-operatively build pointer sets corresponding to addresses within a given set of globals. One particular use case for this is to allow a C++ program to efficiently verify (at each call site) that a vtable pointer is in the set of valid vtable pointers for the class or its derived classes. One way of doing this is for a toolchain component to build, for each class, a bit set that maps to the memory region allocated for the vtables, such that each 1 bit in the bit set maps to a valid vtable for that class, and lay out the vtables next to each other, to minimize the total size of the bit sets. The patch introduces a metadata format for representing pointer sets, an '@llvm.bitset.test' intrinsic and an LTO lowering pass that lays out the globals and builds the bitsets, and documents the new feature. Differential Revision: http://reviews.llvm.org/D7288 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230054 91177308-0d34-0410-b5e6-96231b3b80d8
79 lines
1.9 KiB
C++
79 lines
1.9 KiB
C++
//===- LowerBitSets.h - Bitset lowering pass --------------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines parts of the bitset lowering pass implementation that may
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// be usefully unit tested.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_IPO_LOWERBITSETS_H
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#define LLVM_TRANSFORMS_IPO_LOWERBITSETS_H
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallVector.h"
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#include <stdint.h>
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#include <limits>
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#include <vector>
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namespace llvm {
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class DataLayout;
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class GlobalVariable;
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class Value;
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struct BitSetInfo {
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// The actual bitset.
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std::vector<uint8_t> Bits;
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// The byte offset into the combined global represented by the bitset.
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uint64_t ByteOffset;
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// The size of the bitset in bits.
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uint64_t BitSize;
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// Log2 alignment of the bit set relative to the combined global.
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// For example, a log2 alignment of 3 means that bits in the bitset
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// represent addresses 8 bytes apart.
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unsigned AlignLog2;
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bool isSingleOffset() const {
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return Bits.size() == 1 && Bits[0] == 1;
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}
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bool containsGlobalOffset(uint64_t Offset) const;
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bool containsValue(const DataLayout *DL,
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const DenseMap<GlobalVariable *, uint64_t> &GlobalLayout,
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Value *V, uint64_t COffset = 0) const;
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};
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struct BitSetBuilder {
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SmallVector<uint64_t, 16> Offsets;
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uint64_t Min, Max;
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BitSetBuilder() : Min(std::numeric_limits<uint64_t>::max()), Max(0) {}
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void addOffset(uint64_t Offset) {
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if (Min > Offset)
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Min = Offset;
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if (Max < Offset)
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Max = Offset;
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Offsets.push_back(Offset);
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}
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BitSetInfo build();
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};
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} // namespace llvm
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#endif
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