[WebAssembly] Fix typechecking for else MCInst

[pmatos]

Summary

When hitting an else clause the type Stack should be reset to as it was at the start of the if, without taking into account the Type inserted into the Stack during the then branch of the if.

[aardappel]

thanks for the fix!

llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmTypeCheck.h

class WebAssemblyAsmTypeCheck final {
   bool TypeErrorThisFunction = false;
   bool Unreachable = false;
   bool is64;
 
   void dumpTypeStack(Twine Msg);
   bool typeError(SMLoc ErrorLoc, const Twine &Msg);
   bool popType(SMLoc ErrorLoc, Optional<wasm::ValType> EVT);
   bool getLocal(SMLoc ErrorLoc, const MCInst &Inst, wasm::ValType &Type);
-  bool checkEnd(SMLoc ErrorLoc);
+  bool checkEnd(SMLoc ErrorLoc, bool PopVals = false);
   bool checkSig(SMLoc ErrorLoc, const wasm::WasmSignature &Sig);
   bool getSymRef(SMLoc ErrorLoc, const MCInst &Inst,
                  const MCSymbolRefExpr *&SymRef);
   bool getGlobal(SMLoc ErrorLoc, const MCInst &Inst, wasm::ValType &Type);
 
 public:
   WebAssemblyAsmTypeCheck(MCAsmParser &Parser, const MCInstrInfo &MII, bool is64);
 

llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmTypeCheck.cpp

bool WebAssemblyAsmTypeCheck::getLocal(SMLoc ErrorLoc, const MCInst &Inst,
   auto Local = static_cast<size_t>(Inst.getOperand(0).getImm());
   if (Local >= LocalTypes.size())
     return typeError(ErrorLoc, StringRef("no local type specified for index ") +
                           std::to_string(Local));
   Type = LocalTypes[Local];
   return false;
 }
 
-bool WebAssemblyAsmTypeCheck::checkEnd(SMLoc ErrorLoc) {
+bool WebAssemblyAsmTypeCheck::checkEnd(SMLoc ErrorLoc, bool PopVals) {
   if (LastSig.Returns.size() > Stack.size())
     return typeError(ErrorLoc, "end: insufficient values on the type stack");
+  
+  if (PopVals) {
+    for (auto VT : llvm::reverse(LastSig.Returns)) {
+      if (popType(ErrorLoc, VT)) 
+        return true;
+    }
+    return false;
+  }
+  
   for (size_t i = 0; i < LastSig.Returns.size(); i++) {
     auto EVT = LastSig.Returns[i];
     auto PVT = Stack[Stack.size() - LastSig.Returns.size() + i];
     if (PVT != EVT)
       return typeError(
           ErrorLoc, StringRef("end got ") + WebAssembly::typeToString(PVT) +
                         ", expected " + WebAssembly::typeToString(EVT));
   }
if (getGlobal(ErrorLoc, Inst, Type))
       return true;
     if (popType(ErrorLoc, Type))
       return true;
   } else if (Name == "drop") {
     if (popType(ErrorLoc, {}))
       return true;
   } else if (Name == "end_block" || Name == "end_loop" || Name == "end_if" ||
              Name == "else" || Name == "end_try") {
-    if (checkEnd(ErrorLoc))
+    if (checkEnd(ErrorLoc, Name == "else"))
       return true;
     if (Name == "end_block")
       Unreachable = false;
   } else if (Name == "return") {
     if (endOfFunction(ErrorLoc))
       return true;
   } else if (Name == "call_indirect" || Name == "return_call_indirect") {
     // Function value.

llvm/test/MC/WebAssembly/typechecking-else.s

+# Check that it converts to .o without errors
+# RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj -mattr=+reference-types < %s
+
+objects:
+    .tabletype objects,externref
+
+handle_value:
+    .hidden handle_value
+    .globl handle_value
+    .type handle_value,@function
+    .functype       handle_value (i32) -> (externref)
+    local.get 0
+    i32.const -1
+    i32.eq
+    if externref
+    ref.null_extern
+    else
+    local.get 0
+    table.get objects
+    end_if
+    end_function