Simplify end implementation

Author: chfast

lib/fizzy/execute.cpp

@@ -549,10 +549,8 @@ ExecutionResult execute(Instance& instance, FuncIdx func_idx, const Value* args,
         }
         case Instr::end:
         {
-            // End execution if it's a final end instruction.
-            if (pc == &code.instructions[code.instructions.size()])
-                goto end;
-            break;
+            assert(pc == &code.instructions[code.instructions.size()]);
+            goto end;
         }
         case Instr::br:
         case Instr::br_if:

lib/fizzy/parser_expr.cpp

@@ -531,7 +531,9 @@ parser_result<Code> parse_expr(const uint8_t* pos, const uint8_t* end, FuncIdx f
 
             if (frame.instruction != Instr::loop)  // If end of block/if/else instruction.
             {
-                // Jump on the matching end instruction.
+                // The position of the "end":
+                // for the outermost implicit function block this is the function's end instruction,
+                // otherwise this is the next instruction after the block's end.
                 const auto target_pc = static_cast<uint32_t>(code.instructions.size());
 
                 if (frame.instruction == Instr::if_ || frame.instruction == Instr::else_)