[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);
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aheejin wrote:

```suggestion
```
`SetjmpTableInsts` (and `SetjmpTableSizeInsts`) is for the SSA updates at the end of the transformation, because in the current version `setjmpTable` and `setjmpTableTableSize` are assigned every time we call `saveSetjmp`. Now that we don't do this I don't think we need to insert it here.

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