[WebAssembly] Add asm.js-style exception handling support

Summary: This patch includes asm.js-style exception handling support for
WebAssembly. The WebAssembly MVP does not have any support for
unwinding or non-local control flow. In order to support C++ exceptions,
emscripten currently uses JavaScript exceptions along with some support
code (written in JavaScript) that is bundled by emscripten with the
generated code.
This scheme lowers exception-related instructions for wasm such that
wasm modules can be compatible with emscripten's existing scheme and
share the support code.

Patch by Heejin Ahn

Differential Revision: https://reviews.llvm.org/D22958

llvm-svn: 277391

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index 32154af3c1c..83ef03a8c75 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -29,10 +29,20 @@ using namespace llvm;
 
 #define DEBUG_TYPE "wasm"
 
+// Emscripten's asm.js-style exception handling
+static cl::opt<bool> EnableEmExceptionHandling(
+    "wasm-em-exception-handling",
+    cl::desc("WebAssembly Emscripten-style exception handling"),
+    cl::init(false));
+
 extern "C" void LLVMInitializeWebAssemblyTarget() {
   // Register the target.
   RegisterTargetMachine<WebAssemblyTargetMachine> X(TheWebAssemblyTarget32);
   RegisterTargetMachine<WebAssemblyTargetMachine> Y(TheWebAssemblyTarget64);
+
+  // Register exception handling pass to opt
+  initializeWebAssemblyLowerEmscriptenExceptionsPass(
+      *PassRegistry::getPassRegistry());
 }
 
 //===----------------------------------------------------------------------===//
@@ -149,6 +159,10 @@ void WebAssemblyPassConfig::addIRPasses() {
   if (getOptLevel() != CodeGenOpt::None)
     addPass(createWebAssemblyOptimizeReturned());
 
+  // Handle exceptions.
+  if (EnableEmExceptionHandling)
+    addPass(createWebAssemblyLowerEmscriptenExceptions());
+
   TargetPassConfig::addIRPasses();
 }