[NFC] Separate bitcode reading for FUNC_CODE_INST_CMPXCHG(_OLD)

[gchatelet]

Summary

This is preparatory work to unable storing alignment for AtomicCmpXchgInst.
See D83136 for context and bug: https://bugs.llvm.org/show_bug.cgi?id=27168

This is the fixed version of D83375, which was submitted and reverted.

llvm/include/llvm/Bitcode/LLVMBitCodes.h

enum FunctionCodes {
   FUNC_CODE_INST_INDIRECTBR = 31,       // INDIRECTBR: [opty, op0, op1, ...]
   // 32 is unused.
   FUNC_CODE_DEBUG_LOC_AGAIN = 33, // DEBUG_LOC_AGAIN
 
   FUNC_CODE_INST_CALL = 34, // CALL:    [attr, cc, fnty, fnid, args...]
 
   FUNC_CODE_DEBUG_LOC = 35,        // DEBUG_LOC:  [Line,Col,ScopeVal, IAVal]
   FUNC_CODE_INST_FENCE = 36,       // FENCE: [ordering, synchscope]
-  FUNC_CODE_INST_CMPXCHG_OLD = 37, // CMPXCHG: [ptrty,ptr,cmp,new, align, vol,
-                                   //           ordering, synchscope]
+  FUNC_CODE_INST_CMPXCHG_OLD = 37, // CMPXCHG: [ptrty, ptr, cmp, val, vol,
+                                   //            ordering, synchscope,
+                                   //            failure_ordering?, weak?]
   FUNC_CODE_INST_ATOMICRMW = 38,   // ATOMICRMW: [ptrty,ptr,val, operation,
                                    //             align, vol,
                                    //             ordering, synchscope]
   FUNC_CODE_INST_RESUME = 39,      // RESUME:     [opval]
   FUNC_CODE_INST_LANDINGPAD_OLD =
       40,                         // LANDINGPAD: [ty,val,val,num,id0,val0...]
   FUNC_CODE_INST_LOADATOMIC = 41, // LOAD: [opty, op, align, vol,
                                   //        ordering, synchscope]
   FUNC_CODE_INST_STOREATOMIC_OLD = 42, // STORE: [ptrty,ptr,val, align, vol
                                        //         ordering, synchscope]
   FUNC_CODE_INST_GEP = 43,             // GEP:  [inbounds, n x operands]
   FUNC_CODE_INST_STORE = 44,       // STORE: [ptrty,ptr,valty,val, align, vol]
   FUNC_CODE_INST_STOREATOMIC = 45, // STORE: [ptrty,ptr,val, align, vol
-  FUNC_CODE_INST_CMPXCHG = 46,     // CMPXCHG: [ptrty,ptr,valty,cmp,new, align,
-                                   //           vol,ordering,synchscope]
+  FUNC_CODE_INST_CMPXCHG = 46,     // CMPXCHG: [ptrty, ptr, cmp, val, vol,
+                                   //           success_ordering, synchscope,
+                                   //           failure_ordering, weak]
   FUNC_CODE_INST_LANDINGPAD = 47,  // LANDINGPAD: [ty,val,num,id0,val0...]
   FUNC_CODE_INST_CLEANUPRET = 48,  // CLEANUPRET: [val] or [val,bb#]
   FUNC_CODE_INST_CATCHRET = 49,    // CATCHRET: [val,bb#]
   FUNC_CODE_INST_CATCHPAD = 50,    // CATCHPAD: [bb#,bb#,num,args...]
   FUNC_CODE_INST_CLEANUPPAD = 51,  // CLEANUPPAD: [num,args...]
   FUNC_CODE_INST_CATCHSWITCH =
       52, // CATCHSWITCH: [num,args...] or [num,args...,bb]
   // 53 is unused.

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

AttributeList getAttributes(unsigned i) const {
     if (i-1 < MAttributes.size())
       return MAttributes[i-1];
     return AttributeList();
   }
 
   /// Read a value/type pair out of the specified record from slot 'Slot'.
   /// Increment Slot past the number of slots used in the record. Return true on
   /// failure.
-  bool getValueTypePair(SmallVectorImpl<uint64_t> &Record, unsigned &Slot,
+  bool getValueTypePair(const SmallVectorImpl<uint64_t> &Record, unsigned &Slot,
                         unsigned InstNum, Value *&ResVal,
                         Type **FullTy = nullptr) {
     if (Slot == Record.size()) return true;
     unsigned ValNo = (unsigned)Record[Slot++];
     // Adjust the ValNo, if it was encoded relative to the InstNum.
     if (UseRelativeIDs)
       ValNo = InstNum - ValNo;
     if (ValNo < InstNum) {
bool popValue(SmallVectorImpl<uint64_t> &Record, unsigned &Slot,
     if (getValue(Record, Slot, InstNum, Ty, ResVal))
       return true;
     // All values currently take a single record slot.
     ++Slot;
     return false;
   }
 
   /// Like popValue, but does not increment the Slot number.
-  bool getValue(SmallVectorImpl<uint64_t> &Record, unsigned Slot,
+  bool getValue(const SmallVectorImpl<uint64_t> &Record, unsigned Slot,
                 unsigned InstNum, Type *Ty, Value *&ResVal) {
     ResVal = getValue(Record, Slot, InstNum, Ty);
     return ResVal == nullptr;
   }
 
   /// Version of getValue that returns ResVal directly, or 0 if there is an
   /// error.
-  Value *getValue(SmallVectorImpl<uint64_t> &Record, unsigned Slot,
+  Value *getValue(const SmallVectorImpl<uint64_t> &Record, unsigned Slot,
                   unsigned InstNum, Type *Ty) {
     if (Slot == Record.size()) return nullptr;
     unsigned ValNo = (unsigned)Record[Slot];
     // Adjust the ValNo, if it was encoded relative to the InstNum.
     if (UseRelativeIDs)
       ValNo = InstNum - ValNo;
     return getFnValueByID(ValNo, Ty);
   }
 
   /// Like getValue, but decodes signed VBRs.
-  Value *getValueSigned(SmallVectorImpl<uint64_t> &Record, unsigned Slot,
+  Value *getValueSigned(const SmallVectorImpl<uint64_t> &Record, unsigned Slot,
                         unsigned InstNum, Type *Ty) {
     if (Slot == Record.size()) return nullptr;
     unsigned ValNo = (unsigned)decodeSignRotatedValue(Record[Slot]);
     // Adjust the ValNo, if it was encoded relative to the InstNum.
     if (UseRelativeIDs)
       ValNo = InstNum - ValNo;
     return getFnValueByID(ValNo, Ty);
   }
case bitc::FUNC_CODE_INST_STOREATOMIC_OLD: {
       if (Error Err = parseAlignmentValue(Record[OpNum], Align))
         return Err;
       if (!Align)
         return error("Alignment missing from atomic store");
       I = new StoreInst(Val, Ptr, Record[OpNum + 1], *Align, Ordering, SSID);
       InstructionList.push_back(I);
       break;
     }
-    case bitc::FUNC_CODE_INST_CMPXCHG_OLD:
-    case bitc::FUNC_CODE_INST_CMPXCHG: {
-      // CMPXCHG:[ptrty, ptr, cmp, new, vol, successordering, ssid,
-      //          failureordering?, isweak?]
+    case bitc::FUNC_CODE_INST_CMPXCHG_OLD: {
+      // CMPXCHG_OLD: [ptrty, ptr, cmp, val, vol, ordering, synchscope,
+      // failure_ordering?, weak?]
+      const size_t NumRecords = Record.size();
       unsigned OpNum = 0;
-      Value *Ptr, *Cmp, *New;
+      Value *Ptr = nullptr;
       if (getValueTypePair(Record, OpNum, NextValueNo, Ptr, &FullTy))
         return error("Invalid record");
 
       if (!isa<PointerType>(Ptr->getType()))
         return error("Cmpxchg operand is not a pointer type");
 
-      if (BitCode == bitc::FUNC_CODE_INST_CMPXCHG) {
-        if (getValueTypePair(Record, OpNum, NextValueNo, Cmp, &FullTy))
-          return error("Invalid record");
-      } else if (popValue(Record, OpNum, NextValueNo,
-                          getPointerElementFlatType(FullTy), Cmp))
+      Value *Cmp = nullptr;
+      if (popValue(Record, OpNum, NextValueNo,
         return error("Invalid record");
-      else
-        FullTy = cast<PointerType>(FullTy)->getElementType();
+
 
+      Value *New = nullptr;
       if (popValue(Record, OpNum, NextValueNo, Cmp->getType(), New) ||
-          Record.size() < OpNum + 3 || Record.size() > OpNum + 5)
+          NumRecords < OpNum + 3 || NumRecords > OpNum + 5)
         return error("Invalid record");
 
-      AtomicOrdering SuccessOrdering = getDecodedOrdering(Record[OpNum + 1]);
+      const AtomicOrdering SuccessOrdering =
+          getDecodedOrdering(Record[OpNum + 1]);
       if (SuccessOrdering == AtomicOrdering::NotAtomic ||
           SuccessOrdering == AtomicOrdering::Unordered)
         return error("Invalid record");
-      SyncScope::ID SSID = getDecodedSyncScopeID(Record[OpNum + 2]);
+
+      const SyncScope::ID SSID = getDecodedSyncScopeID(Record[OpNum + 2]);
 
       if (Error Err = typeCheckLoadStoreInst(Cmp->getType(), Ptr->getType()))
         return Err;
-      AtomicOrdering FailureOrdering;
-      if (Record.size() < 7)
-        FailureOrdering =
-            AtomicCmpXchgInst::getStrongestFailureOrdering(SuccessOrdering);
-      else
-        FailureOrdering = getDecodedOrdering(Record[OpNum + 3]);
 
-      Align Alignment(
+      const AtomicOrdering FailureOrdering =
+          NumRecords < 7
+              ? AtomicCmpXchgInst::getStrongestFailureOrdering(SuccessOrdering)
+              : getDecodedOrdering(Record[OpNum + 3]);
+
+      const Align Alignment(
           TheModule->getDataLayout().getTypeStoreSize(Cmp->getType()));
+
       I = new AtomicCmpXchgInst(Ptr, Cmp, New, Alignment, SuccessOrdering,
                                 FailureOrdering, SSID);
-      FullTy = StructType::get(Context, {FullTy, Type::getInt1Ty(Context)});
       cast<AtomicCmpXchgInst>(I)->setVolatile(Record[OpNum]);
+      FullTy = StructType::get(Context, {FullTy, Type::getInt1Ty(Context)});
 
-      if (Record.size() < 8) {
+      if (NumRecords < 8) {
         // Before weak cmpxchgs existed, the instruction simply returned the
         // value loaded from memory, so bitcode files from that era will be
         // expecting the first component of a modern cmpxchg.
         CurBB->getInstList().push_back(I);
         I = ExtractValueInst::Create(I, 0);
         FullTy = cast<StructType>(FullTy)->getElementType(0);
       } else {
-        cast<AtomicCmpXchgInst>(I)->setWeak(Record[OpNum+4]);
+        cast<AtomicCmpXchgInst>(I)->setWeak(Record[OpNum + 4]);
       }
 
       InstructionList.push_back(I);
       break;
     }
+    case bitc::FUNC_CODE_INST_CMPXCHG: {
+      // CMPXCHG: [ptrty, ptr, cmp, val, vol, success_ordering, synchscope,
+      // failure_ordering, weak]
+      const size_t NumRecords = Record.size();
+      unsigned OpNum = 0;
+      Value *Ptr = nullptr;
+      if (getValueTypePair(Record, OpNum, NextValueNo, Ptr, &FullTy))
+        return error("Invalid record");
+
+      if (!isa<PointerType>(Ptr->getType()))
+        return error("Cmpxchg operand is not a pointer type");
+
+      Value *Cmp = nullptr;
+      if (getValueTypePair(Record, OpNum, NextValueNo, Cmp, &FullTy))
+        return error("Invalid record");
+
+      Value *Val = nullptr;
+      if (popValue(Record, OpNum, NextValueNo, Cmp->getType(), Val) ||
+          NumRecords < OpNum + 3 || NumRecords > OpNum + 5)
+        return error("Invalid record");
+
+      const AtomicOrdering SuccessOrdering =
+          getDecodedOrdering(Record[OpNum + 1]);
+      if (SuccessOrdering == AtomicOrdering::NotAtomic ||
+          SuccessOrdering == AtomicOrdering::Unordered)
+        return error("Invalid record");
+
+      const SyncScope::ID SSID = getDecodedSyncScopeID(Record[OpNum + 2]);
+
+      if (Error Err = typeCheckLoadStoreInst(Cmp->getType(), Ptr->getType()))
+        return Err;
+
+      const AtomicOrdering FailureOrdering =
+          getDecodedOrdering(Record[OpNum + 3]);
+
+      const Align Alignment(
+          TheModule->getDataLayout().getTypeStoreSize(Cmp->getType()));
+
+      I = new AtomicCmpXchgInst(Ptr, Cmp, Val, Alignment, SuccessOrdering,
+                                FailureOrdering, SSID);
+      FullTy = StructType::get(Context, {FullTy, Type::getInt1Ty(Context)});
+      cast<AtomicCmpXchgInst>(I)->setVolatile(Record[OpNum]);
+      cast<AtomicCmpXchgInst>(I)->setWeak(Record[OpNum + 4]);
+
+      InstructionList.push_back(I);
+      break;
+    }
     case bitc::FUNC_CODE_INST_ATOMICRMW: {
       // ATOMICRMW:[ptrty, ptr, val, op, vol, ordering, ssid]
       unsigned OpNum = 0;
       Value *Ptr, *Val;
       if (getValueTypePair(Record, OpNum, NextValueNo, Ptr, &FullTy) ||
           !isa<PointerType>(Ptr->getType()) ||
           popValue(Record, OpNum, NextValueNo,
                    getPointerElementFlatType(FullTy), Val) ||