[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

1 files changed, 14 insertions, 9 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrAtomics.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrAtomics.td
index 64415658ed8..fd50f59c44b 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrAtomics.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrAtomics.td
@@ -12,19 +12,23 @@
 ///
 //===----------------------------------------------------------------------===//
 
-// TODO: Implement atomic instructions.
-
-//===----------------------------------------------------------------------===//
-// Atomic fences
-//===----------------------------------------------------------------------===//
-
-// TODO: add atomic fences here...
-
 //===----------------------------------------------------------------------===//
 // Atomic loads
 //===----------------------------------------------------------------------===//
 
-// TODO: add atomic loads here...
+let Defs = [ARGUMENTS] in {
+// TODO: add the rest of the atomic loads
+// TODO: factor out 0xfe atomic prefix?
+def ATOMIC_LOAD_I32 : ATOMIC_I<(outs I32:$dst),
+                        (ins P2Align:$p2align, offset32_op:$off, I32:$addr),
+                        [], "i32.atomic.load\t$dst, ${off}(${addr})${p2align}",
+                        0xfe10>;
+} // Defs = [ARGUMENTS]
+
+// Select loads with no constant offset.
+let Predicates = [HasAtomics] in {
+def : Pat<(i32 (atomic_load I32:$addr)), (ATOMIC_LOAD_I32 0, 0, $addr)>;
+}
 
 //===----------------------------------------------------------------------===//
 // Atomic stores
@@ -45,3 +49,4 @@
 // Store-release-exclusives.
 
 // And clear exclusive.
+