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

[Heejin Ahn via cfe-commits]

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@@ -1291,19 +1327,29 @@ bool WebAssemblyLowerEmscriptenEHSjLj::runSjLjOnFunction(Function &F) {
   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);
+  Instruction *SetjmpTable;
+  if (EnableWasmAltSjLj) {
+    // This alloca'ed pointer is used by the runtime to identify function
+    // inovactions. It's just for pointer comparisons. It will never
+    // be dereferenced.
+    SetjmpTable = IRB.CreateAlloca(IRB.getInt32Ty());
+    SetjmpTable->setDebugLoc(FirstDL);
+    SetjmpTableInsts.push_back(SetjmpTable);
+  } else {
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aheejin wrote:

https://github.com/llvm/llvm-project/blob/578e66ac45dfcc5c739f3525bfb82d71282d925c/llvm/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp#L1278-L1293
This can be moved into this `else` part too. Also we don't need to create `SetjmpTableSize`, in which case we should do something like `IRB.setInsertPoint(Entry.getTerminator()` instead.

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