[Bitstream] Check that there is enough space for blob

Instead of simply assuming that it will be zero. I double checked
that the bitstream reader doesn't have any special handling for
all-zero blobs, it will always write out the full contents.

1 files changed, 3 insertions, 7 deletions

diff --git a/llvm/lib/Bitstream/Reader/BitstreamReader.cpp b/llvm/lib/Bitstream/Reader/BitstreamReader.cpp
index f924790..b2da7e7 100644
--- a/llvm/lib/Bitstream/Reader/BitstreamReader.cpp
+++ b/llvm/lib/Bitstream/Reader/BitstreamReader.cpp
@@ -331,13 +331,9 @@ Expected<unsigned> BitstreamCursor::readRecord(unsigned AbbrevID,
     size_t CurBitPos = GetCurrentBitNo();
     const size_t NewEnd = CurBitPos + alignTo(NumElts, 4) * 8;
 
-    // If this would read off the end of the bitcode file, just set the
-    // record to empty and return.
-    if (!canSkipToPos(NewEnd/8)) {
-      Vals.append(NumElts, 0);
-      skipToEnd();
-      break;
-    }
+    // Make sure the bitstream is large enough to contain the blob.
+    if (!canSkipToPos(NewEnd/8))
+      return error("Blob ends too soon");
 
     // Otherwise, inform the streamer that we need these bytes in memory.  Skip
     // over tail padding first, in case jumping to NewEnd invalidates the Blob