Facilitate use of `bugpoint` on `-pnacl-sjlj-eh` by adding a hidden option to ignore undefined EH s…

lib/Transforms/NaCl/PNaClSjLjEH.cpp

 //===- PNaClSjLjEH.cpp - Lower C++ exception handling to use setjmp()------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // The PNaClSjLjEH pass is part of an implementation of C++ exception
@@ skipping 139 matching lines @@
         Frame(NULL), FrameJmpBuf(NULL), FrameNextPtr(NULL), FrameExcInfo(NULL),
         EHResumeFunc(NULL) {}
 
     Value *createSetjmpWrappedCall(InvokeInst *Invoke);
     void expandInvokeInst(InvokeInst *Invoke);
     void expandResumeInst(ResumeInst *Resume);
     void expandFunc();
   };
 }
 
+static cl::opt<bool>
+AllowUndefEhFuncs("allow-undef-pnacl-eh",
+                  cl::desc("Allow required EH symbols, like `__pnacl_eh_resume`, "
+                           "to be undefined"),
+                  cl::init(false), cl::Hidden);
+
 char PNaClSjLjEH::ID = 0;
 INITIALIZE_PASS(PNaClSjLjEH, "pnacl-sjlj-eh",
                 "Lower C++ exception handling to use setjmp()",
                 false, false)
 
 static const int kPNaClJmpBufSize = 1024;
 static const int kPNaClJmpBufAlign = 8;
 
 void FuncRewriter::initializeFrame() {
   if (FrameInitialized)
     return;
   FrameInitialized = true;
   Module *M = Func->getParent();
 
   SetjmpIntrinsic = Intrinsic::getDeclaration(M, Intrinsic::nacl_setjmp);
 
   Value *EHStackTlsVarUncast = M->getGlobalVariable("__pnacl_eh_stack");
-  if (!EHStackTlsVarUncast)
-    report_fatal_error("__pnacl_eh_stack not defined");
+  if (!EHStackTlsVarUncast) {
+    if (!AllowUndefEhFuncs) {
+      report_fatal_error("__pnacl_eh_stack not defined");
+    } else {
+      EHStackTlsVarUncast =
+        M->getOrInsertGlobal("__pnacl_eh_stack",
+                             ExceptionFrameTy->getPointerTo());
+    }
+  }
   EHStackTlsVar = new BitCastInst(
       EHStackTlsVarUncast, ExceptionFrameTy->getPointerTo()->getPointerTo(),
       "pnacl_eh_stack");
   Func->getEntryBlock().getInstList().push_front(EHStackTlsVar);
 
   // Allocate the new exception frame.  This is reused across all
   // invoke instructions in the function.
   Type *I32 = Type::getInt32Ty(M->getContext());
   Frame = new AllocaInst(ExceptionFrameTy, ConstantInt::get(I32, 1),
                          kPNaClJmpBufAlign, "invoke_frame");
@@ skipping 176 matching lines @@
   CopyDebug(BranchInst::Create(Invoke->getNormalDest(), Invoke->getUnwindDest(),
                                IsZero, Invoke),
             Invoke);
 
   Invoke->eraseFromParent();
 }
 
 void FuncRewriter::expandResumeInst(ResumeInst *Resume) {
   if (!EHResumeFunc) {
     EHResumeFunc = Func->getParent()->getFunction("__pnacl_eh_resume");
-    if (!EHResumeFunc)
+  }
+  if (!EHResumeFunc) {
+    if (AllowUndefEhFuncs) {
+      // Create a declaration of __pnacl_eh_resume:
+      Module* M = Func->getParent();
+      LLVMContext& C = M->getContext();
+      auto Args = std::vector<Type*>(1, Type::getInt8Ty(C)->getPointerTo());
+      EHResumeFunc =
+        Function::Create(FunctionType::get(Type::getVoidTy(C),
+                                           Args,
+                                           false),
+                         GlobalValue::ExternalLinkage,
+                         "__pnacl_eh_resume");
+      M->getFunctionList().insertAfter(Func, EHResumeFunc);
+      EHResumeFunc->setDoesNotReturn();
+    } else {
       report_fatal_error("__pnacl_eh_resume() not defined");
+    }
   }
 
   // The "resume" instruction gets passed the landingpad's full result
   // (struct LandingPadResult above).  Extract the exception_obj field
   // to pass to __pnacl_eh_resume(), which doesn't need the
   // matched_clause_id field.
   unsigned Indexes[] = { 0 };
   Value *ExceptionPtr =
       CopyDebug(ExtractValueInst::Create(Resume->getValue(), Indexes,
                                          "resume_exc", Resume), Resume);
@@ skipping 69 matching lines @@
     FuncRewriter Rewriter(ExceptionFrameTy, &ExcInfoWriter, Func);
     Rewriter.expandFunc();
   }
   ExcInfoWriter.defineGlobalVariables(&M);
   return true;
 }
 
 ModulePass *llvm::createPNaClSjLjEHPass() {
   return new PNaClSjLjEH();
 }