[Bitstream] Improve error propagation from ReadVBR

Differential Revision: https://reviews.llvm.org/D119307

Author: jkorous-apple

llvm/lib/Bitstream/Reader/BitstreamReader.cpp

@@ -220,7 +220,9 @@ Expected<unsigned> BitstreamCursor::readRecord(unsigned AbbrevID,
     uint32_t Code = MaybeCode.get();
     Expected<uint32_t> MaybeNumElts = ReadVBR(6);
     if (!MaybeNumElts)
-      return MaybeNumElts.takeError();
+      return error(("Failed to read size: " +
+                    toString(std::move(MaybeNumElts.takeError())))
+                       .c_str());
     uint32_t NumElts = MaybeNumElts.get();
     if (!isSizePlausible(NumElts))
       return error("Size is not plausible");
@@ -275,7 +277,9 @@ Expected<unsigned> BitstreamCursor::readRecord(unsigned AbbrevID,
       // Array case.  Read the number of elements as a vbr6.
       Expected<uint32_t> MaybeNumElts = ReadVBR(6);
       if (!MaybeNumElts)
-        return MaybeNumElts.takeError();
+        return error(("Failed to read size: " +
+                      toString(std::move(MaybeNumElts.takeError())))
+                         .c_str());
       uint32_t NumElts = MaybeNumElts.get();
       if (!isSizePlausible(NumElts))
         return error("Size is not plausible");

llvm/test/Bitcode/invalid.test

@@ -275,7 +275,7 @@ INVALID-VALUE-SYMBOL-TABLE: Invalid value reference in symbol table
 RUN: not llvm-dis -disable-output %p/Inputs/unterminated-vbr.bc 2>&1 | \
 RUN:   FileCheck --check-prefix=UNTERMINATED-VBR %s
 
-UNTERMINATED-VBR: Unterminated VBR
+UNTERMINATED-VBR: Failed to read size: Unterminated VBR
 
 RUN: not llvm-dis -disable-output %p/Inputs/comdat-name-too-large.bc 2>&1 | \
 RUN:   FileCheck --check-prefix=COMDAT-NAME-TOO-LARGE %s