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Read 64 bits at a time in the bitcode reader.

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The reading of 64 bit values could still be optimized, but at least this cuts
down on the number of virtual calls to fetch more data.

llvm-svn: 221865
This commit is contained in:
Rafael Espindola 2014-11-13 07:23:22 +00:00
parent 477bb4ae3d
commit ad6b4ce7dc
3 changed files with 17 additions and 20 deletions
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18
include/llvm/Bitcode/BitstreamReader.h
View File

@ -177,11 +177,11 @@ class BitstreamCursor {
/// follow the word size of the host machine for efficiency. We use word_t in /// follow the word size of the host machine for efficiency. We use word_t in
/// places that are aware of this to make it perfectly explicit what is going /// places that are aware of this to make it perfectly explicit what is going
/// on. /// on.
typedef uint32_t word_t; typedef size_t word_t;
word_t CurWord; word_t CurWord;
/// This is the number of bits in CurWord that are valid. This is always from /// This is the number of bits in CurWord that are valid. This is always from
/// [0...31/63] inclusive (depending on word size). /// [0...bits_of(size_t)-1] inclusive.
unsigned BitsInCurWord; unsigned BitsInCurWord;
// This is the declared size of code values used for the current block, in // This is the declared size of code values used for the current block, in
@ -333,7 +333,6 @@ public:
Size = NextChar; Size = NextChar;
return; return;
} }
assert(BytesRead == sizeof(Array));
// Handle big-endian byte-swapping if necessary. // Handle big-endian byte-swapping if necessary.
support::detail::packed_endian_specific_integral< support::detail::packed_endian_specific_integral<
@ -341,20 +340,22 @@ public:
memcpy(&EndianValue, Array, sizeof(Array)); memcpy(&EndianValue, Array, sizeof(Array));
CurWord = EndianValue; CurWord = EndianValue;
NextChar += sizeof(word_t); NextChar += BytesRead;
BitsInCurWord = sizeof(word_t) * 8; BitsInCurWord = BytesRead * 8;
} }
uint32_t Read(unsigned NumBits) { uint32_t Read(unsigned NumBits) {
assert(NumBits && NumBits <= 32 && assert(NumBits && NumBits <= 32 &&
"Cannot return zero or more than 32 bits!"); "Cannot return zero or more than 32 bits!");
static const unsigned Mask = sizeof(word_t) > 4 ? 0x3f : 0x1f;
// If the field is fully contained by CurWord, return it quickly. // If the field is fully contained by CurWord, return it quickly.
if (BitsInCurWord >= NumBits) { if (BitsInCurWord >= NumBits) {
uint32_t R = uint32_t(CurWord) & (~0U >> (32-NumBits)); uint32_t R = uint32_t(CurWord) & (~0U >> (32-NumBits));
// Use a mask to avoid undefined behavior. // Use a mask to avoid undefined behavior.
CurWord >>= (NumBits & 0x1f); CurWord >>= (NumBits & Mask);
BitsInCurWord -= NumBits; BitsInCurWord -= NumBits;
return R; return R;
@ -369,10 +370,11 @@ public:
if (BitsLeft > BitsInCurWord) if (BitsLeft > BitsInCurWord)
return 0; return 0;
uint32_t R2 = uint32_t(CurWord) & (~0U >> (sizeof(word_t) * 8 - BitsLeft)); uint32_t R2 =
uint32_t(CurWord) & (~word_t(0) >> (sizeof(word_t) * 8 - BitsLeft));
// Use a mask to avoid undefined behavior. // Use a mask to avoid undefined behavior.
CurWord >>= (BitsLeft & 0x1f); CurWord >>= (BitsLeft & Mask);
BitsInCurWord -= BitsLeft; BitsInCurWord -= BitsLeft;

12
include/llvm/Support/StreamingMemoryObject.h
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@ -71,14 +71,10 @@ private:
size_t bytes = Streamer->GetBytes(&Bytes[BytesRead + BytesSkipped], size_t bytes = Streamer->GetBytes(&Bytes[BytesRead + BytesSkipped],
kChunkSize); kChunkSize);
BytesRead += bytes; BytesRead += bytes;
if (bytes < kChunkSize) { if (BytesRead <= Pos) { // reached EOF/ran out of bytes
assert((!ObjectSize || BytesRead >= Pos) && ObjectSize = BytesRead;
"Unexpected short read fetching bitcode"); EOFReached = true;
if (BytesRead <= Pos) { // reached EOF/ran out of bytes return false;
ObjectSize = BytesRead;
EOFReached = true;
return false;
}
} }
} }
return true; return true;

7
lib/Support/StreamingMemoryObject.cpp
View File

@ -90,13 +90,12 @@ uint64_t StreamingMemoryObject::getExtent() const {
uint64_t StreamingMemoryObject::readBytes(uint8_t *Buf, uint64_t Size, uint64_t StreamingMemoryObject::readBytes(uint8_t *Buf, uint64_t Size,
uint64_t Address) const { uint64_t Address) const {
fetchToPos(Address + Size - 1); fetchToPos(Address + Size - 1);
uint64_t BufferSize = Bytes.size() - BytesSkipped; if (Address >= BytesRead)
if (Address >= BufferSize)
return 0; return 0;
uint64_t End = Address + Size; uint64_t End = Address + Size;
if (End > BufferSize) if (End > BytesRead)
End = BufferSize; End = BytesRead;
Size = End - Address; Size = End - Address;
assert(Size >= 0); assert(Size >= 0);
memcpy(Buf, &Bytes[Address + BytesSkipped], Size); memcpy(Buf, &Bytes[Address + BytesSkipped], Size);