[WebAssembly] Add target feature for atomics

Summary:
This tracks the WebAssembly threads feature proposal at
https://github.com/WebAssembly/threads/blob/master/proposals/threads/Overview.md

Differential Revision: https://reviews.llvm.org/D37300

llvm-svn: 312145
diff --git a/llvm/lib/Target/WebAssembly/WebAssembly.td b/llvm/lib/Target/WebAssembly/WebAssembly.td
index f647349..50445b7 100644
--- a/llvm/lib/Target/WebAssembly/WebAssembly.td
+++ b/llvm/lib/Target/WebAssembly/WebAssembly.td
@@ -25,6 +25,8 @@
 
 def FeatureSIMD128 : SubtargetFeature<"simd128", "HasSIMD128", "true",
                                       "Enable 128-bit SIMD">;
+def FeatureAtomics : SubtargetFeature<"atomics", "HasAtomics", "true",
+                                      "Enable Atomics">;
 
 //===----------------------------------------------------------------------===//
 // Architectures.
@@ -55,7 +57,8 @@
 def : ProcessorModel<"generic", NoSchedModel, []>;
 
 // Latest and greatest experimental version of WebAssembly. Bugs included!
-def : ProcessorModel<"bleeding-edge", NoSchedModel, [FeatureSIMD128]>;
+def : ProcessorModel<"bleeding-edge", NoSchedModel,
+                      [FeatureSIMD128, FeatureAtomics]>;
 
 //===----------------------------------------------------------------------===//
 // Target Declaration