[WebAssembly] Add asm.js-style setjmp/longjmp handling for wasm (reland r280302)

Summary: This patch adds asm.js-style setjmp/longjmp handling support for WebAssembly. It also uses JavaScript's try and catch mechanism.

Reviewers: jpp, dschuff

Subscribers: jfb, dschuff

Differential Revision: https://reviews.llvm.org/D24121

llvm-svn: 280415

1 files changed, 13 insertions, 1 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
index 3aa25932f84..ee60cf3cd1f 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp
@@ -165,7 +165,19 @@ void WebAssemblyPassConfig::addIRPasses() {
   if (getOptLevel() != CodeGenOpt::None)
     addPass(createWebAssemblyOptimizeReturned());
 
-  // Handle exceptions.
+  // If exception handling is not enabled and setjmp/longjmp handling is
+  // enabled, we lower invokes into calls and delete unreachable landingpad
+  // blocks. Lowering invokes when there is no EH support is done in
+  // TargetPassConfig::addPassesToHandleExceptions, but this runs after this
+  // function and SjLj handling expects all invokes to be lowered before.
+  if (!EnableEmException) {
+    addPass(createLowerInvokePass());
+    // The lower invoke pass may create unreachable code. Remove it in order not
+    // to process dead blocks in setjmp/longjmp handling.
+    addPass(createUnreachableBlockEliminationPass());
+  }
+
+  // Handle exceptions and setjmp/longjmp if enabled.
   if (EnableEmException || EnableEmSjLj)
     addPass(createWebAssemblyLowerEmscriptenEHSjLj(EnableEmException,
                                                    EnableEmSjLj));