[WebAssembly] Error when wasm EH is used with Emscripten EH/SjLj

[aheejin]

Summary

• Error out when both Emscripten EH and wasm EH are used together, i.e., both -enable-emscripten-cxx-exceptions and -exception-model=wasm are given together. This will not happen if you use Emscripten, but this can happen when you call llc manually with wrong set of arguments.
• Currently we don't yet support using wasm EH with Emscripten SjLj. Unlike -enable-emscripten-cxx-exceptions which is turned on only when you use emcc -s DISABLE_EXCEPTION_CATCHING=0, -enable-emscripten-sjlj is turned on by Emscripten by default. So we error out only when it is turned on and setjmp or longjmp is actually used.

llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp

bool WebAssemblyLowerEmscriptenEHSjLj::runOnModule(Module &M) {
   IRBuilder<> IRB(C);
 
   Function *SetjmpF = M.getFunction("setjmp");
   Function *LongjmpF = M.getFunction("longjmp");
   bool SetjmpUsed = SetjmpF && !SetjmpF->use_empty();
   bool LongjmpUsed = LongjmpF && !LongjmpF->use_empty();
   bool DoSjLj = EnableSjLj && (SetjmpUsed || LongjmpUsed);
 
-  if ((EnableEH || DoSjLj) &&
-      Triple(M.getTargetTriple()).getArch() == Triple::wasm64)
-    report_fatal_error("Emscripten EH/SjLj is not supported with wasm64 yet");
-
   auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
   assert(TPC && "Expected a TargetPassConfig");
   auto &TM = TPC->getTM<WebAssemblyTargetMachine>();
 
+  if ((EnableEH || DoSjLj) &&
+      Triple(M.getTargetTriple()).getArch() == Triple::wasm64)
+    report_fatal_error("Emscripten EH/SjLj is not supported with wasm64 yet");
+  if (EnableEH && TM.Options.ExceptionModel == ExceptionHandling::Wasm)
+    report_fatal_error("-exception-model=wasm not allowed with "
+                       "-enable-emscripten-cxx-exceptions");
+  if (DoSjLj && TM.Options.ExceptionModel == ExceptionHandling::Wasm)
+    report_fatal_error("Emscripten SjLj is not supported with Wasm EH yet");
+
   // Declare (or get) global variables __THREW__, __threwValue, and
   // getTempRet0/setTempRet0 function which are used in common for both
   // exception handling and setjmp/longjmp handling
   ThrewGV = getGlobalVariableI32(M, IRB, TM, "__THREW__");
   ThrewValueGV = getGlobalVariableI32(M, IRB, TM, "__threwValue");
   GetTempRet0Func = getEmscriptenFunction(
       FunctionType::get(IRB.getInt32Ty(), false), "getTempRet0", &M);
   SetTempRet0Func = getEmscriptenFunction(

llvm/test/CodeGen/WebAssembly/lower-em-ehsjlj-options.ll

 ; RUN: llc < %s -enable-emscripten-cxx-exceptions | FileCheck %s --check-prefix=EH
 ; RUN: llc < %s -enable-emscripten-sjlj | FileCheck %s --check-prefix=SJLJ
 ; RUN: llc < %s | FileCheck %s --check-prefix=NONE
 ; RUN: not --crash llc < %s -enable-emscripten-cxx-exceptions -mtriple=wasm64-unknown-unknown 2>&1 | FileCheck %s --check-prefix=WASM64-EH
 ; RUN: not --crash llc < %s -enable-emscripten-sjlj -mtriple=wasm64-unknown-unknown 2>&1 | FileCheck %s --check-prefix=WASM64-SJLJ
+; RUN: not --crash llc < %s -enable-emscripten-cxx-exceptions -exception-model=wasm 2>&1 | FileCheck %s --check-prefix=WASM-EH-EM-EH
+; RUN: not --crash llc < %s -enable-emscripten-sjlj -exception-model=wasm 2>&1 | FileCheck %s --check-prefix=WASM-EH-EM-SJLJ
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
 
 %struct.__jmp_buf_tag = type { [6 x i32], i32, [32 x i32] }
 
 define void @exception() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
 ; EH-LABEL:   type exception,@function

 ; SJLJ: .import_module  emscripten_longjmp, env
 ; SJLJ: .import_name  emscripten_longjmp, emscripten_longjmp
 ; SJLJ-NOT: .functype  emscripten_longjmp_jmpbuf
 ; SJLJ-NOT: .import_module  emscripten_longjmp_jmpbuf
 ; SJLJ-NOT: .import_name  emscripten_longjmp_jmpbuf
 
 ; WASM64-EH: LLVM ERROR: Emscripten EH/SjLj is not supported with wasm64 yet
 ; WASM64-SJLJ: LLVM ERROR: Emscripten EH/SjLj is not supported with wasm64 yet
+; WASM-EH-EM-EH: LLVM ERROR: -exception-model=wasm not allowed with -enable-emscripten-cxx-exceptions
+; WASM-EH-EM-SJLJ: LLVM ERROR: Emscripten SjLj is not supported with Wasm EH yet