[WebAssembly] Optimize away return instructions using fallthroughs.

This saves a small amount of code size, and is a first small step toward
passing values on the stack across block boundaries.

Differential Review: http://reviews.llvm.org/D20450

llvm-svn: 270294
diff --git a/llvm/test/CodeGen/WebAssembly/switch.ll b/llvm/test/CodeGen/WebAssembly/switch.ll
index 20af644..8355bc8 100644
--- a/llvm/test/CodeGen/WebAssembly/switch.ll
+++ b/llvm/test/CodeGen/WebAssembly/switch.ll
@@ -1,4 +1,4 @@
-; RUN: llc < %s -asm-verbose=false -disable-block-placement -verify-machineinstrs | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -disable-block-placement -verify-machineinstrs | FileCheck %s
 
 ; Test switch instructions. Block placement is disabled because it reorders
 ; the blocks in a way that isn't interesting here.