compile with -Wunused-but-set-variable

Our open-source build compiles with these warnings, so they cause spew when building from github. And I think they are good to catch programmer error.

hphp/runtime/vm/jit/codegen.cpp

@@ -5419,7 +5419,9 @@ void genCodeForTrace(Trace* trace,
   CodegenState state(irFactory, regs, live_regs, lifetime, asmInfo);
 
   // Returns: whether a block has already been emitted.
-  auto isEmitted = [&](Block* block) { return state.addresses[block]; };
+  DEBUG_ONLY auto isEmitted = [&](Block* block) {
+    return state.addresses[block];
+  };
 
   /*
    * Emit the given block on the supplied assembler.  The `nextBlock'

hphp/runtime/vm/jit/linearscan.cpp

@@ -321,7 +321,7 @@ PhysReg::Type LinearScan::getRegType(const SSATmp* tmp, int locIdx) const {
 
   if (packed_tv) return PhysReg::GP;
 
-  Type tmpType = tmp->type();
+  DEBUG_ONLY Type tmpType = tmp->type();
 
   uint32_t tmpId = tmp->id();
 

hphp/runtime/vm/jit/translator.cpp

@@ -943,10 +943,6 @@ getDynLocType(const vector<DynLocation*>& inputs,
         }
 
         const bool setElem = mcodeMaybeArrayKey(ni->immVecM[0]);
-        const bool setNewElem = ni->immVecM[0] == MW;
-        const Type keyType =
-          setNewElem ? Type::None
-                     : Type::fromRuntimeType(inputs[2]->rtt);
         const Type valType = Type::fromRuntimeType(inputs[0]->rtt);
         if (setElem && baseType.maybe(Type::Str)) {
           if (baseType.isString()) {

hphp/runtime/vm/jit/vectortranslator.cpp

@@ -182,14 +182,6 @@ void VectorEffects::init(Opcode op, const Type origBase,
     }
   }
 
-  // Setting an element with a base of one of these types will either succeed
-  // (with possible promotion) or fatal
-  const Type okBase = Type::Str | Type::Arr | Type::Obj;
-
-  // Setting an element with one of these types as the key will fail, issue a
-  // warning, and evaulate to null.
-  const Type badArrKey = Type::Arr | Type::Obj;
-
   // The final baseType should be a pointer/box iff the input was
   baseType = baseBoxed ? baseType.box() : baseType;
   baseType = basePtr   ? baseType.ptr() : baseType;