}
}
+ // The 'cmpxchg' instruction returns an aggregate containing the old value and
+ // an i1 which indicates whether or not we successfully did the swap.
+ //
+ // Replace comparisons between the old value and the expected value with the
+ // indicator that 'cmpxchg' returns.
+ //
+ // N.B. This transform is only valid when the 'cmpxchg' is not permitted to
+ // spuriously fail. In those cases, the old value may equal the expected
+ // value but it is possible for the swap to not occur.
+ if (I.getPredicate() == ICmpInst::ICMP_EQ)
+ if (auto *EVI = dyn_cast<ExtractValueInst>(Op0))
+ if (auto *ACXI = dyn_cast<AtomicCmpXchgInst>(EVI->getAggregateOperand()))
+ if (EVI->getIndices()[0] == 0 && ACXI->getCompareOperand() == Op1 &&
+ !ACXI->isWeak())
+ return ExtractValueInst::Create(ACXI, 1);
+
{
Value *X; ConstantInt *Cst;
// icmp X+Cst, X