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Diffstat (limited to 'include/llvm/Transforms/IPO/LowerBitSets.h')
| -rw-r--r-- | include/llvm/Transforms/IPO/LowerBitSets.h | 201 |
1 files changed, 0 insertions, 201 deletions
diff --git a/include/llvm/Transforms/IPO/LowerBitSets.h b/include/llvm/Transforms/IPO/LowerBitSets.h deleted file mode 100644 index e5fb7b98fcb3..000000000000 --- a/include/llvm/Transforms/IPO/LowerBitSets.h +++ /dev/null @@ -1,201 +0,0 @@ -//===- LowerBitSets.h - Bitset lowering pass --------------------*- C++ -*-===// -// -// The LLVM Compiler Infrastructure -// -// This file is distributed under the University of Illinois Open Source -// License. See LICENSE.TXT for details. -// -//===----------------------------------------------------------------------===// -// -// This file defines parts of the bitset lowering pass implementation that may -// be usefully unit tested. -// -//===----------------------------------------------------------------------===// - -#ifndef LLVM_TRANSFORMS_IPO_LOWERBITSETS_H -#define LLVM_TRANSFORMS_IPO_LOWERBITSETS_H - -#include "llvm/ADT/DenseMap.h" -#include "llvm/ADT/SmallVector.h" - -#include <stdint.h> -#include <limits> -#include <set> -#include <vector> - -namespace llvm { - -class DataLayout; -class GlobalObject; -class Value; -class raw_ostream; - -struct BitSetInfo { - // The indices of the set bits in the bitset. - std::set<uint64_t> Bits; - - // The byte offset into the combined global represented by the bitset. - uint64_t ByteOffset; - - // The size of the bitset in bits. - uint64_t BitSize; - - // Log2 alignment of the bit set relative to the combined global. - // For example, a log2 alignment of 3 means that bits in the bitset - // represent addresses 8 bytes apart. - unsigned AlignLog2; - - bool isSingleOffset() const { - return Bits.size() == 1; - } - - bool isAllOnes() const { - return Bits.size() == BitSize; - } - - bool containsGlobalOffset(uint64_t Offset) const; - - bool containsValue(const DataLayout &DL, - const DenseMap<GlobalObject *, uint64_t> &GlobalLayout, - Value *V, uint64_t COffset = 0) const; - - void print(raw_ostream &OS) const; -}; - -struct BitSetBuilder { - SmallVector<uint64_t, 16> Offsets; - uint64_t Min, Max; - - BitSetBuilder() : Min(std::numeric_limits<uint64_t>::max()), Max(0) {} - - void addOffset(uint64_t Offset) { - if (Min > Offset) - Min = Offset; - if (Max < Offset) - Max = Offset; - - Offsets.push_back(Offset); - } - - BitSetInfo build(); -}; - -/// This class implements a layout algorithm for globals referenced by bit sets -/// that tries to keep members of small bit sets together. This can -/// significantly reduce bit set sizes in many cases. -/// -/// It works by assembling fragments of layout from sets of referenced globals. -/// Each set of referenced globals causes the algorithm to create a new -/// fragment, which is assembled by appending each referenced global in the set -/// into the fragment. If a referenced global has already been referenced by an -/// fragment created earlier, we instead delete that fragment and append its -/// contents into the fragment we are assembling. -/// -/// By starting with the smallest fragments, we minimize the size of the -/// fragments that are copied into larger fragments. This is most intuitively -/// thought about when considering the case where the globals are virtual tables -/// and the bit sets represent their derived classes: in a single inheritance -/// hierarchy, the optimum layout would involve a depth-first search of the -/// class hierarchy (and in fact the computed layout ends up looking a lot like -/// a DFS), but a naive DFS would not work well in the presence of multiple -/// inheritance. This aspect of the algorithm ends up fitting smaller -/// hierarchies inside larger ones where that would be beneficial. -/// -/// For example, consider this class hierarchy: -/// -/// A B -/// \ / | \ -/// C D E -/// -/// We have five bit sets: bsA (A, C), bsB (B, C, D, E), bsC (C), bsD (D) and -/// bsE (E). If we laid out our objects by DFS traversing B followed by A, our -/// layout would be {B, C, D, E, A}. This is optimal for bsB as it needs to -/// cover the only 4 objects in its hierarchy, but not for bsA as it needs to -/// cover 5 objects, i.e. the entire layout. Our algorithm proceeds as follows: -/// -/// Add bsC, fragments {{C}} -/// Add bsD, fragments {{C}, {D}} -/// Add bsE, fragments {{C}, {D}, {E}} -/// Add bsA, fragments {{A, C}, {D}, {E}} -/// Add bsB, fragments {{B, A, C, D, E}} -/// -/// This layout is optimal for bsA, as it now only needs to cover two (i.e. 3 -/// fewer) objects, at the cost of bsB needing to cover 1 more object. -/// -/// The bit set lowering pass assigns an object index to each object that needs -/// to be laid out, and calls addFragment for each bit set passing the object -/// indices of its referenced globals. It then assembles a layout from the -/// computed layout in the Fragments field. -struct GlobalLayoutBuilder { - /// The computed layout. Each element of this vector contains a fragment of - /// layout (which may be empty) consisting of object indices. - std::vector<std::vector<uint64_t>> Fragments; - - /// Mapping from object index to fragment index. - std::vector<uint64_t> FragmentMap; - - GlobalLayoutBuilder(uint64_t NumObjects) - : Fragments(1), FragmentMap(NumObjects) {} - - /// Add F to the layout while trying to keep its indices contiguous. - /// If a previously seen fragment uses any of F's indices, that - /// fragment will be laid out inside F. - void addFragment(const std::set<uint64_t> &F); -}; - -/// This class is used to build a byte array containing overlapping bit sets. By -/// loading from indexed offsets into the byte array and applying a mask, a -/// program can test bits from the bit set with a relatively short instruction -/// sequence. For example, suppose we have 15 bit sets to lay out: -/// -/// A (16 bits), B (15 bits), C (14 bits), D (13 bits), E (12 bits), -/// F (11 bits), G (10 bits), H (9 bits), I (7 bits), J (6 bits), K (5 bits), -/// L (4 bits), M (3 bits), N (2 bits), O (1 bit) -/// -/// These bits can be laid out in a 16-byte array like this: -/// -/// Byte Offset -/// 0123456789ABCDEF -/// Bit -/// 7 HHHHHHHHHIIIIIII -/// 6 GGGGGGGGGGJJJJJJ -/// 5 FFFFFFFFFFFKKKKK -/// 4 EEEEEEEEEEEELLLL -/// 3 DDDDDDDDDDDDDMMM -/// 2 CCCCCCCCCCCCCCNN -/// 1 BBBBBBBBBBBBBBBO -/// 0 AAAAAAAAAAAAAAAA -/// -/// For example, to test bit X of A, we evaluate ((bits[X] & 1) != 0), or to -/// test bit X of I, we evaluate ((bits[9 + X] & 0x80) != 0). This can be done -/// in 1-2 machine instructions on x86, or 4-6 instructions on ARM. -/// -/// This is a byte array, rather than (say) a 2-byte array or a 4-byte array, -/// because for one thing it gives us better packing (the more bins there are, -/// the less evenly they will be filled), and for another, the instruction -/// sequences can be slightly shorter, both on x86 and ARM. -struct ByteArrayBuilder { - /// The byte array built so far. - std::vector<uint8_t> Bytes; - - enum { BitsPerByte = 8 }; - - /// The number of bytes allocated so far for each of the bits. - uint64_t BitAllocs[BitsPerByte]; - - ByteArrayBuilder() { - memset(BitAllocs, 0, sizeof(BitAllocs)); - } - - /// Allocate BitSize bits in the byte array where Bits contains the bits to - /// set. AllocByteOffset is set to the offset within the byte array and - /// AllocMask is set to the bitmask for those bits. This uses the LPT (Longest - /// Processing Time) multiprocessor scheduling algorithm to lay out the bits - /// efficiently; the pass allocates bit sets in decreasing size order. - void allocate(const std::set<uint64_t> &Bits, uint64_t BitSize, - uint64_t &AllocByteOffset, uint8_t &AllocMask); -}; - -} // namespace llvm - -#endif |