[WebAssembly] Fix use of cast vs dyn_cast

[mehdi_amini]

LGTM, thanks!

llvm/trunk/lib/MC/WasmObjectWriter.cpp

if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
     IsPCRel = true;
     C -= K;
   }
 
   // We either rejected the fixup or folded B into C at this point.
   const MCSymbolRefExpr *RefA = Target.getSymA();
   const auto *SymA = RefA ? cast<MCSymbolWasm>(&RefA->getSymbol()) : nullptr;
 
-  bool ViaWeakRef = false;
   if (SymA && SymA->isVariable()) {
     const MCExpr *Expr = SymA->getVariableValue();
-    if (const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr)) {
-      if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) {
-        SymA = cast<MCSymbolWasm>(&Inner->getSymbol());
-        ViaWeakRef = true;
-      }
-    }
+    const auto *Inner = cast<MCSymbolRefExpr>(Expr);
+    if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
+      llvm_unreachable("weakref used in reloc not yet implemented");
   }
 
   // Put any constant offset in an addend. Offsets can be negative, and
   // LLVM expects wrapping, in contrast to wasm's immediates which can't
   // be negative and don't wrap.
   FixedValue = 0;
 
-  if (SymA) {
-    if (ViaWeakRef)
-      llvm_unreachable("weakref used in reloc not yet implemented");
-    else
-      SymA->setUsedInReloc();
-  }
+  if (SymA)
 
   assert(!IsPCRel);
   assert(SymA);
 
   unsigned Type = getRelocType(Target, Fixup);
 
   WasmRelocationEntry Rec(FixupOffset, SymA, C, Type, &FixupSection);
   DEBUG(dbgs() << "WasmReloc: " << Rec << "\n");

 }
 
 uint32_t WasmObjectWriter::registerFunctionType(const MCSymbolWasm& Symbol) {
   assert(Symbol.isFunction());
 
   WasmFunctionType F;
   if (Symbol.isVariable()) {
     const MCExpr *Expr = Symbol.getVariableValue();
-    auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
+    auto *Inner = cast<MCSymbolRefExpr>(Expr);
     const auto *ResolvedSym = cast<MCSymbolWasm>(&Inner->getSymbol());
     F.Returns = ResolvedSym->getReturns();
     F.Params = ResolvedSym->getParams();
   } else {
     F.Returns = Symbol.getReturns();
     F.Params = Symbol.getParams();
   }
 
void WasmObjectWriter::writeObject(MCAssembler &Asm,
   for (const MCSymbol &S : Asm.symbols()) {
     if (!S.isVariable())
       continue;
     assert(S.isDefined(/*SetUsed=*/false));
 
     const auto &WS = static_cast<const MCSymbolWasm &>(S);
     // Find the target symbol of this weak alias and export that index
     const MCExpr *Expr = WS.getVariableValue();
-    auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
+    auto *Inner = cast<MCSymbolRefExpr>(Expr);
     const auto *ResolvedSym = cast<MCSymbolWasm>(&Inner->getSymbol());
     DEBUG(dbgs() << WS.getName() << ": weak alias of '" << *ResolvedSym << "'\n");
     assert(SymbolIndices.count(ResolvedSym) > 0);
     uint32_t Index = SymbolIndices.find(ResolvedSym)->second;
     DEBUG(dbgs() << "  -> index:" << Index << "\n");
 
     WasmExport Export;
     Export.FieldName = WS.getName();