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

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZOperators.td b/llvm/lib/Target/SystemZ/SystemZOperators.td
index 31cabaa3413..771fbc32f3c 100644
--- a/llvm/lib/Target/SystemZ/SystemZOperators.td
+++ b/llvm/lib/Target/SystemZ/SystemZOperators.td
@@ -119,6 +119,9 @@ def z_sdivrem64         : SDNode<"SystemZISD::SDIVREM64", SDT_ZGR128Binary64>;
 def z_udivrem32         : SDNode<"SystemZISD::UDIVREM32", SDT_ZGR128Binary32>;
 def z_udivrem64         : SDNode<"SystemZISD::UDIVREM64", SDT_ZGR128Binary64>;
 
+def z_serialize         : SDNode<"SystemZISD::SERIALIZE", SDTNone,
+                                 [SDNPHasChain, SDNPMayStore]>;
+
 class AtomicWOp<string name, SDTypeProfile profile = SDT_ZAtomicLoadBinaryW>
   : SDNode<"SystemZISD::"##name, profile,
            [SDNPHasChain, SDNPMayStore, SDNPMayLoad, SDNPMemOperand]>;