[clang] [llvm] [WebAssembly] Implement an alternative translation for -wasm-enable-sjlj (PR #84137)

[Heejin Ahn via cfe-commits]

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@@ -1268,42 +1259,21 @@ bool WebAssemblyLowerEmscriptenEHSjLj::runSjLjOnFunction(Function &F) {
   LLVMContext &C = F.getContext();
   IRBuilder<> IRB(C);
   SmallVector<Instruction *, 64> ToErase;
-  // Vector of %setjmpTable values
-  SmallVector<Instruction *, 4> SetjmpTableInsts;
-  // Vector of %setjmpTableSize values
-  SmallVector<Instruction *, 4> SetjmpTableSizeInsts;
 
   // Setjmp preparation
 
-  // This instruction effectively means %setjmpTableSize = 4.
-  // We create this as an instruction intentionally, and we don't want to fold
-  // this instruction to a constant 4, because this value will be used in
-  // SSAUpdater.AddAvailableValue(...) later.
   BasicBlock *Entry = &F.getEntryBlock();
   DebugLoc FirstDL = getOrCreateDebugLoc(&*Entry->begin(), F.getSubprogram());
   SplitBlock(Entry, &*Entry->getFirstInsertionPt());
 
-  BinaryOperator *SetjmpTableSize =
-      BinaryOperator::Create(Instruction::Add, IRB.getInt32(4), IRB.getInt32(0),
-                             "setjmpTableSize", Entry->getTerminator());
-  SetjmpTableSize->setDebugLoc(FirstDL);
-  // setjmpTable = (int *) malloc(40);
-  Type *IntPtrTy = getAddrIntType(&M);
-  Constant *size = ConstantInt::get(IntPtrTy, 40);
-  IRB.SetInsertPoint(SetjmpTableSize);
-  auto *SetjmpTable = IRB.CreateMalloc(IntPtrTy, IRB.getInt32Ty(), size,
-                                       nullptr, nullptr, "setjmpTable");
-  SetjmpTable->setDebugLoc(FirstDL);
-  // CallInst::CreateMalloc may return a bitcast instruction if the result types
-  // mismatch. We need to set the debug loc for the original call too.
-  auto *MallocCall = SetjmpTable->stripPointerCasts();
-  if (auto *MallocCallI = dyn_cast<Instruction>(MallocCall)) {
-    MallocCallI->setDebugLoc(FirstDL);
-  }
-  // setjmpTable[0] = 0;
-  IRB.CreateStore(IRB.getInt32(0), SetjmpTable);
-  SetjmpTableInsts.push_back(SetjmpTable);
-  SetjmpTableSizeInsts.push_back(SetjmpTableSize);
+  Instruction *FunctionInvocationId;
+  IRB.SetInsertPoint(Entry->getTerminator());
+  // This alloca'ed pointer is used by the runtime to identify function
+  // inovactions. It's just for pointer comparisons. It will never
+  // be dereferenced.
----------------
aheejin wrote:

```suggestion
  // invocations. It's just for pointer comparisons. It will never be
  // dereferenced.
```

https://github.com/llvm/llvm-project/pull/84137