[WebAssembly] Update SIMD binary arithmetic

Add missing SIMD types (v2f64) and binary ops. Also adds
tablegen support for automatically prepending prefix byte to SIMD
opcodes.

Differential Revision: https://reviews.llvm.org/D50292

Patch by Thomas Lively

llvm-svn: 339186
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
index 2ec595e..b74eb45 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
@@ -256,7 +256,9 @@
   case MVT::v16i8:
   case MVT::v8i16:
   case MVT::v4i32:
+  case MVT::v2i64:
   case MVT::v4f32:
+  case MVT::v2f64:
     retType = WebAssembly::ExprType::V128;
     break;
   case MVT::ExceptRef: retType = WebAssembly::ExprType::ExceptRef; break;