Bitcode: Collect all MDString records into a single blob

Optimize output of MDStrings in bitcode.  This emits them in big blocks
(currently 1024) in a pair of records:
  - BULK_STRING_SIZES: the sizes of the strings in the block, and
  - BULK_STRING_DATA: a single blob, which is the concatenation of all
    the strings.

Inspired by Mehdi's similar patch, http://reviews.llvm.org/D18342, this
should (a) slightly reduce bitcode size, since there is less record
overhead, and (b) greatly improve reading speed, since blobs are super
cheap to deserialize.

I needed to add support for blobs to streaming input to get the test
suite passing.
  - StreamingMemoryObject::getPointer reads ahead and returns the
    address of the blob.
  - To avoid a possible reallocation of StreamingMemoryObject::Bytes,
    BitstreamCursor::readRecord needs to move the call to JumpToEnd
    forward so that getPointer is the last bitstream operation.

llvm-svn: 264409

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Support/StreamingMemoryObject.cpp b/llvm/lib/Support/StreamingMemoryObject.cpp
index 5a44e624eb8..fb566179486 100644
--- a/llvm/lib/Support/StreamingMemoryObject.cpp
+++ b/llvm/lib/Support/StreamingMemoryObject.cpp
@@ -104,6 +104,12 @@ uint64_t StreamingMemoryObject::readBytes(uint8_t *Buf, uint64_t Size,
   return Size;
 }
 
+const uint8_t *StreamingMemoryObject::getPointer(uint64_t Address,
+                                                 uint64_t Size) const {
+  fetchToPos(Address + Size - 1);
+  return &Bytes[Address + BytesSkipped];
+}
+
 bool StreamingMemoryObject::dropLeadingBytes(size_t s) {
   if (BytesRead < s) return true;
   BytesSkipped = s;