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a6ffc80357
The implementation is fairly obvious. This is preparation for using
some blobs in bitcode.
For clarity (and perhaps future-proofing?), I moved the call to
JumpToBit in BitstreamCursor::readRecord ahead of calling
MemoryObject::getPointer, since JumpToBit can theoretically (a) read
bytes, which (b) invalidates the blob pointer.
This isn't strictly necessary the two memory objects we have:
- The return of RawMemoryObject::getPointer is valid until the memory
object is destroyed.
- StreamingMemoryObject::getPointer is valid until the next chunk is
read from the stream. Since the JumpToBit call is only going ahead
to a word boundary, we'll never load another chunk.
However, reordering makes it clear by inspection that the blob returned
by BitstreamCursor::readRecord will be valid.
I added some tests for StreamingMemoryObject::getPointer and
BitstreamCursor::readRecord.
llvm-svn: 264549
88 lines
3.3 KiB
C++
88 lines
3.3 KiB
C++
//===- StreamingMemoryObject.h - Streamable data interface -----*- 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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#ifndef LLVM_SUPPORT_STREAMINGMEMORYOBJECT_H
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#define LLVM_SUPPORT_STREAMINGMEMORYOBJECT_H
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/DataStream.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/MemoryObject.h"
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#include <memory>
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#include <vector>
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namespace llvm {
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/// Interface to data which is actually streamed from a DataStreamer. In
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/// addition to inherited members, it has the dropLeadingBytes and
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/// setKnownObjectSize methods which are not applicable to non-streamed objects.
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class StreamingMemoryObject : public MemoryObject {
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public:
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StreamingMemoryObject(std::unique_ptr<DataStreamer> Streamer);
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uint64_t getExtent() const override;
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uint64_t readBytes(uint8_t *Buf, uint64_t Size,
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uint64_t Address) const override;
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const uint8_t *getPointer(uint64_t Address, uint64_t Size) const override;
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bool isValidAddress(uint64_t address) const override;
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/// Drop s bytes from the front of the stream, pushing the positions of the
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/// remaining bytes down by s. This is used to skip past the bitcode header,
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/// since we don't know a priori if it's present, and we can't put bytes
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/// back into the stream once we've read them.
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bool dropLeadingBytes(size_t s);
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/// If the data object size is known in advance, many of the operations can
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/// be made more efficient, so this method should be called before reading
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/// starts (although it can be called anytime).
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void setKnownObjectSize(size_t size);
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/// The number of bytes read at a time from the data streamer.
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static const uint32_t kChunkSize = 4096 * 4;
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private:
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mutable std::vector<unsigned char> Bytes;
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std::unique_ptr<DataStreamer> Streamer;
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mutable size_t BytesRead; // Bytes read from stream
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size_t BytesSkipped;// Bytes skipped at start of stream (e.g. wrapper/header)
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mutable size_t ObjectSize; // 0 if unknown, set if wrapper seen or EOF reached
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mutable bool EOFReached;
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// Fetch enough bytes such that Pos can be read (i.e. BytesRead >
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// Pos). Returns true if Pos can be read. Unlike most of the
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// functions in BitcodeReader, returns true on success. Most of the
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// requests will be small, but we fetch at kChunkSize bytes at a
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// time to avoid making too many potentially expensive GetBytes
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// calls.
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bool fetchToPos(size_t Pos) const {
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while (Pos >= BytesRead) {
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if (EOFReached)
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return false;
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Bytes.resize(BytesRead + BytesSkipped + kChunkSize);
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size_t bytes = Streamer->GetBytes(&Bytes[BytesRead + BytesSkipped],
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kChunkSize);
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BytesRead += bytes;
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if (bytes == 0) { // reached EOF/ran out of bytes
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if (ObjectSize == 0)
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ObjectSize = BytesRead;
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EOFReached = true;
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}
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}
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return !ObjectSize || Pos < ObjectSize;
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}
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StreamingMemoryObject(const StreamingMemoryObject&) = delete;
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void operator=(const StreamingMemoryObject&) = delete;
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};
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MemoryObject *getNonStreamedMemoryObject(
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const unsigned char *Start, const unsigned char *End);
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}
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#endif // STREAMINGMEMORYOBJECT_H_
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