Add TargetLowering::prepareVolatileOrAtomicLoad
One unusual feature of the z architecture is that the result of a
previous load can be reused indefinitely for subsequent loads, even if
a cache-coherent store to that location is performed by another CPU.
A special serializing instruction must be used if you want to force
a load to be reattempted.
Since volatile loads are not supposed to be omitted in this way,
we should insert a serializing instruction before each such load.
The same goes for atomic loads.
The patch implements this at the IR->DAG boundary, in a similar way
to atomic fences. It is a no-op for targets other than SystemZ.
llvm-svn: 196905
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 34b7df5..c63a88b 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -3400,7 +3400,7 @@
SDValue Root;
bool ConstantMemory = false;
- if (I.isVolatile() || NumValues > MaxParallelChains)
+ if (isVolatile || NumValues > MaxParallelChains)
// Serialize volatile loads with other side effects.
Root = getRoot();
else if (AA->pointsToConstantMemory(
@@ -3413,6 +3413,10 @@
Root = DAG.getRoot();
}
+ const TargetLowering *TLI = TM.getTargetLowering();
+ if (isVolatile)
+ Root = TLI->prepareVolatileOrAtomicLoad(Root, getCurSDLoc(), DAG);
+
SmallVector<SDValue, 4> Values(NumValues);
SmallVector<SDValue, 4> Chains(std::min(unsigned(MaxParallelChains),
NumValues));
@@ -3637,6 +3641,7 @@
if (I.getAlignment() < VT.getSizeInBits() / 8)
report_fatal_error("Cannot generate unaligned atomic load");
+ InChain = TLI->prepareVolatileOrAtomicLoad(InChain, dl, DAG);
SDValue L =
DAG.getAtomic(ISD::ATOMIC_LOAD, dl, VT, VT, InChain,
getValue(I.getPointerOperand()),