[WebAssembly] Fix resume-only case in Emscripten EH (#36)

Summary:
D72308 incorrectly assumed `resume` cannot exist without a `landingpad`,
which is not true. This sets `Changed` to true whenever we make changes
to a function, including creating a call to `__resumeException` within a
function without a landing pad.

Reviewers: tlively

Subscribers: dschuff, sbc100, jgravelle-google, hiraditya, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73308

Co-authored-by: Heejin Ahn <aheejin@gmail.com>

Author: 2 people

llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp

@@ -755,6 +755,7 @@ bool WebAssemblyLowerEmscriptenEHSjLj::runEHOnFunction(Function &F) {
     auto *II = dyn_cast<InvokeInst>(BB.getTerminator());
     if (!II)
       continue;
+    Changed = true;
     LandingPads.insert(II->getLandingPadInst());
     IRB.SetInsertPoint(II);
 
@@ -795,6 +796,7 @@ bool WebAssemblyLowerEmscriptenEHSjLj::runEHOnFunction(Function &F) {
       auto *RI = dyn_cast<ResumeInst>(&I);
       if (!RI)
         continue;
+      Changed = true;
 
       // Split the input into legal values
       Value *Input = RI->getValue();
@@ -819,6 +821,7 @@ bool WebAssemblyLowerEmscriptenEHSjLj::runEHOnFunction(Function &F) {
         continue;
       if (Callee->getIntrinsicID() != Intrinsic::eh_typeid_for)
         continue;
+      Changed = true;
 
       IRB.SetInsertPoint(CI);
       CallInst *NewCI =
@@ -834,7 +837,7 @@ bool WebAssemblyLowerEmscriptenEHSjLj::runEHOnFunction(Function &F) {
     if (auto *LPI = dyn_cast<LandingPadInst>(I))
       LandingPads.insert(LPI);
   }
-  Changed = !LandingPads.empty();
+  Changed |= !LandingPads.empty();
 
   // Handle all the landingpad for this function together, as multiple invokes
   // may share a single lp

llvm/test/CodeGen/WebAssembly/lower-em-exceptions-lpad-only.ll

@@ -0,0 +1,17 @@
+; RUN: opt < %s -wasm-lower-em-ehsjlj -S | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+; Checks if a module that only contains a resume but not an invoke works
+; correctly and does not crash.
+; CHECK-LABEL: @resume_only
+; CHECK: call void @__resumeException
+define void @resume_only() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+entry:
+  %val0 = insertvalue { i8*, i32 } undef, i8* null, 0
+  %val1 = insertvalue { i8*, i32} %val0, i32 0, 1
+  resume { i8*, i32 } %val1
+}
+
+declare i32 @__gxx_personality_v0(...)