IR: add a second ordering operand to cmpxhg for failure

The syntax for "cmpxchg" should now look something like:

	cmpxchg i32* %addr, i32 42, i32 3 acquire monotonic

where the second ordering argument gives the required semantics in the case
that no exchange takes place. It should be no stronger than the first ordering
constraint and cannot be either "release" or "acq_rel" (since no store will
have taken place).

rdar://problem/15996804

llvm-svn: 203559

1 files changed, 15 insertions, 5 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 5e358d9cc54..eb716660eb4 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -2882,7 +2882,8 @@ error_code BitcodeReader::ParseFunctionBody(Function *F) {
       break;
     }
     case bitc::FUNC_CODE_INST_CMPXCHG: {
-      // CMPXCHG:[ptrty, ptr, cmp, new, vol, ordering, synchscope]
+      // CMPXCHG:[ptrty, ptr, cmp, new, vol, successordering, synchscope,
+      //          failureordering]
       unsigned OpNum = 0;
       Value *Ptr, *Cmp, *New;
       if (getValueTypePair(Record, OpNum, NextValueNo, Ptr) ||
@@ -2890,13 +2891,22 @@ error_code BitcodeReader::ParseFunctionBody(Function *F) {
                     cast<PointerType>(Ptr->getType())->getElementType(), Cmp) ||
           popValue(Record, OpNum, NextValueNo,
                     cast<PointerType>(Ptr->getType())->getElementType(), New) ||
-          OpNum+3 != Record.size())
+          (OpNum + 3 != Record.size() && OpNum + 4 != Record.size()))
         return Error(InvalidRecord);
-      AtomicOrdering Ordering = GetDecodedOrdering(Record[OpNum+1]);
-      if (Ordering == NotAtomic || Ordering == Unordered)
+      AtomicOrdering SuccessOrdering = GetDecodedOrdering(Record[OpNum+1]);
+      if (SuccessOrdering == NotAtomic || SuccessOrdering == Unordered)
         return Error(InvalidRecord);
       SynchronizationScope SynchScope = GetDecodedSynchScope(Record[OpNum+2]);
-      I = new AtomicCmpXchgInst(Ptr, Cmp, New, Ordering, SynchScope);
+
+      AtomicOrdering FailureOrdering;
+      if (Record.size() < 7)
+        FailureOrdering =
+            AtomicCmpXchgInst::getStrongestFailureOrdering(SuccessOrdering);
+      else
+        FailureOrdering = GetDecodedOrdering(Record[OpNum+3]);
+
+      I = new AtomicCmpXchgInst(Ptr, Cmp, New, SuccessOrdering, FailureOrdering,
+                                SynchScope);
       cast<AtomicCmpXchgInst>(I)->setVolatile(Record[OpNum]);
       InstructionList.push_back(I);
       break;