[Verifier] Move some atomicrmw/cmpxchg checks to instruction creation

These checks already exist as asserts when creating the corresponding
instruction. Anybody creating these instructions already need to take
care to not break these checks.

Move the checks for success/failure ordering in cmpxchg from the
verifier to the LLParser and BitcodeReader plus an assert.

Add some tests for cmpxchg ordering. The .bc files are created from the
.ll files with an llvm-as with these checks disabled.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D102803

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -5143,6 +5143,10 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
               ? AtomicCmpXchgInst::getStrongestFailureOrdering(SuccessOrdering)
               : getDecodedOrdering(Record[OpNum + 3]);
 
+      if (FailureOrdering == AtomicOrdering::NotAtomic ||
+          FailureOrdering == AtomicOrdering::Unordered)
+        return error("Invalid record");
+
       const Align Alignment(
           TheModule->getDataLayout().getTypeStoreSize(Cmp->getType()));
 
@@ -5192,9 +5196,8 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
 
       const AtomicOrdering SuccessOrdering =
           getDecodedOrdering(Record[OpNum + 1]);
-      if (SuccessOrdering == AtomicOrdering::NotAtomic ||
-          SuccessOrdering == AtomicOrdering::Unordered)
-        return error("Invalid record");
+      if (!AtomicCmpXchgInst::isValidSuccessOrdering(SuccessOrdering))
+        return error("Invalid cmpxchg success ordering");
 
       const SyncScope::ID SSID = getDecodedSyncScopeID(Record[OpNum + 2]);
 
@@ -5203,6 +5206,8 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
 
       const AtomicOrdering FailureOrdering =
           getDecodedOrdering(Record[OpNum + 3]);
+      if (!AtomicCmpXchgInst::isValidFailureOrdering(FailureOrdering))
+        return error("Invalid cmpxchg failure ordering");
 
       const bool IsWeak = Record[OpNum + 4];