BitcodeReader: Check for unresolved function metadata

A follow-up commit will start using function metadata blocks more
heavily.  This commit adds some error checking to confirm that metadata
is fully resolved before (and after) materializing each function.

This is valid even when reading very old bitcode from before the
metadata/value split.  The global metadata block always came before the
function blocks.  However, in case somehow this causes a regression
(i.e., an old LLVM did produce such bitcode after all) I'm committing
separately.

llvm-svn: 265223

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -123,6 +123,7 @@ public:
 
   void shrinkTo(unsigned N) {
     assert(N <= size() && "Invalid shrinkTo request!");
+    assert(!AnyFwdRefs && "Unexpected forward refs");
     MetadataPtrs.resize(N);
   }
 
@@ -130,6 +131,7 @@ public:
   MDNode *getMDNodeFwdRefOrNull(unsigned Idx);
   void assignValue(Metadata *MD, unsigned Idx);
   void tryToResolveCycles();
+  bool hasFwdRefs() const { return AnyFwdRefs; }
 };
 
 class BitcodeReader : public GVMaterializer {
@@ -1929,6 +1931,9 @@ std::error_code BitcodeReader::parseMetadata(bool ModuleLevel) {
   IsMetadataMaterialized = true;
   unsigned NextMetadataNo = MetadataList.size();
 
+  if (!ModuleLevel && MetadataList.hasFwdRefs())
+    return error("Invalid metadata: fwd refs into function blocks");
+
   if (Stream.EnterSubBlock(bitc::METADATA_BLOCK_ID))
     return error("Invalid record");
 
@@ -3968,6 +3973,10 @@ std::error_code BitcodeReader::parseFunctionBody(Function *F) {
   if (Stream.EnterSubBlock(bitc::FUNCTION_BLOCK_ID))
     return error("Invalid record");
 
+  // Unexpected unresolved metadata when parsing function.
+  if (MetadataList.hasFwdRefs())
+    return error("Invalid function metadata: incoming forward references");
+
   InstructionList.clear();
   unsigned ModuleValueListSize = ValueList.size();
   unsigned ModuleMetadataListSize = MetadataList.size();
@@ -5227,8 +5236,9 @@ OutOfRecordLoop:
     }
   }
 
-  // FIXME: Check for unresolved forward-declared metadata references
-  // and clean up leaks.
+  // Unexpected unresolved metadata about to be dropped.
+  if (MetadataList.hasFwdRefs())
+    return error("Invalid function metadata: outgoing forward refs");
 
   // Trim the value list down to the size it was before we parsed this function.
   ValueList.shrinkTo(ModuleValueListSize);