[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/phi.ll b/llvm/test/CodeGen/WebAssembly/phi.ll
index 00e5859..747ae5c 100644
--- a/llvm/test/CodeGen/WebAssembly/phi.ll
+++ b/llvm/test/CodeGen/WebAssembly/phi.ll
@@ -1,4 +1,4 @@
-; RUN: llc < %s -asm-verbose=false -verify-machineinstrs | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -verify-machineinstrs | FileCheck %s
 
 ; Test that phis are lowered.