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, 7 insertions, 2 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZProcessors.td b/llvm/lib/Target/SystemZ/SystemZProcessors.td
index f241fb0c222..9aed4f9edff 100644
--- a/llvm/lib/Target/SystemZ/SystemZProcessors.td
+++ b/llvm/lib/Target/SystemZ/SystemZProcessors.td
@@ -36,11 +36,16 @@ def FeatureFPExtension : SystemZFeature<
   "Assume that the floating-point extension facility is installed"
 >;
 
+def FeatureFastSerialization : SystemZFeature<
+  "fast-serialization", "FastSerialization",
+  "Assume that the fast-serialization facility is installed"
+>;
+
 def : Processor<"generic", NoItineraries, []>;
 def : Processor<"z10", NoItineraries, []>;
 def : Processor<"z196", NoItineraries,
                 [FeatureDistinctOps, FeatureLoadStoreOnCond, FeatureHighWord,
-                 FeatureFPExtension]>;
+                 FeatureFPExtension, FeatureFastSerialization]>;
 def : Processor<"zEC12", NoItineraries,
                 [FeatureDistinctOps, FeatureLoadStoreOnCond, FeatureHighWord,
-                 FeatureFPExtension]>;
+                 FeatureFPExtension, FeatureFastSerialization]>;