[opaque pointer type] bitcode support for explicit type parameter to the load instruction

Summary:
I've taken my best guess at this, but I've cargo culted in places & so
explanations/corrections would be great.

This seems to pass all the tests (check-all, covering clang and llvm) so I
believe that pretty well exercises both the backwards compatibility and common
(same version) compatibility given the number of checked in bitcode files we
already have. Is that a reasonable approach to testing here? Would some more
explicit tests be desired?

1) is this the right way to do back-compat in this case (looking at the number
  of entries in the bitcode record to disambiguate between the old schema and
  the new?)

2) I don't quite understand the logarithm logic to choose the encoding type of
  the type parameter in the abbreviation description, but I found another
  instruction doing the same thing & it seems to work. Is that the right
  approach?

Reviewers: dexonsmith

Differential Revision: http://reviews.llvm.org/D7655

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230414 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -3574,12 +3574,21 @@ std::error_code BitcodeReader::ParseFunctionBody(Function *F) {
       unsigned OpNum = 0;
       Value *Op;
       if (getValueTypePair(Record, OpNum, NextValueNo, Op) ||
-          OpNum+2 != Record.size())
+          (OpNum + 2 != Record.size() && OpNum + 3 != Record.size()))
         return Error("Invalid record");
+
+      Type *Ty = nullptr;
+      if (OpNum + 3 == Record.size())
+        Ty = getTypeByID(Record[OpNum++]);
+
       unsigned Align;
       if (std::error_code EC = parseAlignmentValue(Record[OpNum], Align))
         return EC;
       I = new LoadInst(Op, "", Record[OpNum+1], Align);
+
+      assert((!Ty || Ty == I->getType()) &&
+             "Explicit type doesn't match pointee type of the first operand");
+
       InstructionList.push_back(I);
       break;
     }
@@ -3588,9 +3597,13 @@ std::error_code BitcodeReader::ParseFunctionBody(Function *F) {
       unsigned OpNum = 0;
       Value *Op;
       if (getValueTypePair(Record, OpNum, NextValueNo, Op) ||
-          OpNum+4 != Record.size())
+          (OpNum + 4 != Record.size() && OpNum + 5 != Record.size()))
         return Error("Invalid record");
 
+      Type *Ty = nullptr;
+      if (OpNum + 5 == Record.size())
+        Ty = getTypeByID(Record[OpNum++]);
+
       AtomicOrdering Ordering = GetDecodedOrdering(Record[OpNum+2]);
       if (Ordering == NotAtomic || Ordering == Release ||
           Ordering == AcquireRelease)
@@ -3603,6 +3616,10 @@ std::error_code BitcodeReader::ParseFunctionBody(Function *F) {
       if (std::error_code EC = parseAlignmentValue(Record[OpNum], Align))
         return EC;
       I = new LoadInst(Op, "", Record[OpNum+1], Align, Ordering, SynchScope);
+
+      assert((!Ty || Ty == I->getType()) &&
+             "Explicit type doesn't match pointee type of the first operand");
+
       InstructionList.push_back(I);
       break;
     }

lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -1871,6 +1871,7 @@ static void WriteInstruction(const Instruction &I, unsigned InstID,
       if (!PushValueAndType(I.getOperand(0), InstID, Vals, VE))  // ptr
         AbbrevToUse = FUNCTION_INST_LOAD_ABBREV;
     }
+    Vals.push_back(VE.getTypeID(I.getType()));
     Vals.push_back(Log2_32(cast<LoadInst>(I).getAlignment())+1);
     Vals.push_back(cast<LoadInst>(I).isVolatile());
     if (cast<LoadInst>(I).isAtomic()) {
@@ -2223,6 +2224,8 @@ static void WriteBlockInfo(const ValueEnumerator &VE, BitstreamWriter &Stream) {
     BitCodeAbbrev *Abbv = new BitCodeAbbrev();
     Abbv->Add(BitCodeAbbrevOp(bitc::FUNC_CODE_INST_LOAD));
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6)); // Ptr
+    Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed,    // dest ty
+                              VE.computeBitsRequiredForTypeIndicies()));
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 4)); // Align
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // volatile
     if (Stream.EmitBlockInfoAbbrev(bitc::FUNCTION_BLOCK_ID,