[WebAssembly] Add -emscripten-cxx-exceptions-whitelist option

[aheejin]

Summary

This patch adds -emscripten-cxx-exceptions-whitelist option to WebAssemblyLowerEmscriptenExceptions pass. This options is the list of function names in which Emscripten-style exception handling is enabled. Depends on D22958.

[dschuff]

lib/Target/WebAssembly/WebAssemblyLowerEmscriptenExceptions.cpp

346

I assume that an empty whitelist means "every function catches exceptions." That's a little bit counterintuitive; I think it would be much clearer just to have an explicit bool (maybe that just gets set in runOnModule) that means "always allow exceptions".

[aheejin]

Address comments

[dschuff]

(LGTM, committed)

lib/Target/WebAssembly/WebAssemblyLowerEmscriptenExceptions.cpp

 #include "llvm/IR/Module.h"
 #include "llvm/Support/raw_ostream.h"
 #include <set>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "wasm-lower-em-exceptions"
 
+static cl::list<std::string>
+    Whitelist("emscripten-cxx-exceptions-whitelist",
+              cl::desc("The list of function names in which Emscripten-style "
+                       "exception handling is enabled (see emscripten "
+                       "EMSCRIPTEN_CATCHING_WHITELIST options)"),
+              cl::CommaSeparated);
+
 namespace {
 class WebAssemblyLowerEmscriptenExceptions final : public ModulePass {
   const char *getPassName() const override {
     return "WebAssembly Lower Emscripten Exceptions";
   }
 
-  bool runOnFunction(Function &F);
+  bool runOnFunction(Function &F, const std::set<std::string> &WhitelistSet);
   // Returns __cxa_find_matching_catch_N function, where N = NumClauses + 2.
   // This is because a landingpad instruction contains two more arguments,
   // a personality function and a cleanup bit, and __cxa_find_matching_catch_N
   // functions are named after the number of arguments in the original
   // landingpad instruction.
   Function *getFindMatchingCatch(Module &M, unsigned NumClauses);
 
   Function *getInvokeWrapper(Module &M, InvokeInst *II);
bool WebAssemblyLowerEmscriptenExceptions::runOnModule(Module &M) {
   ResumeF = Function::Create(ResumeFTy, GlobalValue::ExternalLinkage,
                              "__resumeException", &M);
 
   // Register llvm_eh_typeid_for function
   FunctionType *EHTypeIdTy = FunctionType::get(Int32Ty, Int8PtrTy, false);
   EHTypeIdF = Function::Create(EHTypeIdTy, GlobalValue::ExternalLinkage,
                                "llvm_eh_typeid_for", &M);
 
+  std::set<std::string> WhitelistSet(Whitelist.begin(), Whitelist.end());
+
   bool Changed = false;
   for (Function &F : M) {
     if (F.isDeclaration())
       continue;
-    Changed |= runOnFunction(F);
+    Changed |= runOnFunction(F, WhitelistSet);
   }
 
   if (!Changed)
     return false;
 
   assert(!M.getNamedGlobal("setThrew") && "setThrew already exists");
   assert(!M.getNamedGlobal("setTempRet0") && "setTempRet0 already exists");
 
bool WebAssemblyLowerEmscriptenExceptions::runOnModule(Module &M) {
   EntryBB = BasicBlock::Create(C, "entry", F);
   Builder.SetInsertPoint(EntryBB);
   Builder.CreateStore(&*F->arg_begin(), TempRet0GV);
   Builder.CreateRetVoid();
 
   return true;
 }
 
-bool WebAssemblyLowerEmscriptenExceptions::runOnFunction(Function &F) {
+bool WebAssemblyLowerEmscriptenExceptions::runOnFunction(
+    Function &F, const std::set<std::string> &WhitelistSet) {
   Module &M = *F.getParent();
   LLVMContext &C = F.getContext();
   IRBuilder<> Builder(C);
   bool Changed = false;
   SmallVector<Instruction *, 64> ToErase;
   SmallPtrSet<LandingPadInst *, 32> LandingPads;
-  bool AllowExceptions = true; // will later change based on whitelist option
+  bool AllowExceptions =
+      WhitelistSet.empty() || WhitelistSet.count(F.getName());
 
   for (BasicBlock &BB : F) {
     auto *II = dyn_cast<InvokeInst>(BB.getTerminator());
     if (!II)
       continue;
     Changed = true;
     LandingPads.insert(II->getLandingPadInst());
     Builder.SetInsertPoint(II);

test/CodeGen/WebAssembly/lower-em-exceptions-whitelist.ll

+; RUN: opt < %s -wasm-lower-em-exceptions -emscripten-cxx-exceptions-whitelist=do_catch -S | FileCheck %s
+
+define void @dont_catch() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+; CHECK-LABEL: @dont_catch(
+entry:
+  invoke void @foo()
+          to label %invoke.cont unwind label %lpad
+; CHECK: entry:
+; CHECK-NEXT: call void @foo()
+; CHECK-NEXT: br label %invoke.cont
+
+invoke.cont:                                      ; preds = %entry
+  br label %try.cont
+
+lpad:                                             ; preds = %entry
+  %0 = landingpad { i8*, i32 }
+          catch i8* null
+  %1 = extractvalue { i8*, i32 } %0, 0
+  %2 = extractvalue { i8*, i32 } %0, 1
+  br label %catch
+
+catch:                                            ; preds = %lpad
+  %3 = call i8* @__cxa_begin_catch(i8* %1)
+  call void @__cxa_end_catch()
+  br label %try.cont
+
+try.cont:                                         ; preds = %catch, %invoke.cont
+  ret void
+}
+
+define void @do_catch() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+; CHECK-LABEL: @do_catch(
+entry:
+  invoke void @foo()
+          to label %invoke.cont unwind label %lpad
+; CHECK: entry:
+; CHECK-NEXT: store i1 false, i1*
+; CHECK-NEXT: call void @__invoke_void(void ()* @foo)
+
+invoke.cont:                                      ; preds = %entry
+  br label %try.cont
+
+lpad:                                             ; preds = %entry
+  %0 = landingpad { i8*, i32 }
+          catch i8* null
+  %1 = extractvalue { i8*, i32 } %0, 0
+  %2 = extractvalue { i8*, i32 } %0, 1
+  br label %catch
+
+catch:                                            ; preds = %lpad
+  %3 = call i8* @__cxa_begin_catch(i8* %1)
+  call void @__cxa_end_catch()
+  br label %try.cont
+
+try.cont:                                         ; preds = %catch, %invoke.cont
+  ret void
+}
+
+declare void @foo()
+declare i32 @__gxx_personality_v0(...)
+declare i8* @__cxa_begin_catch(i8*)
+declare void @__cxa_end_catch()