[FixBug] Don't instantiate symbol for primitive functions (#291)

Previously, if a primitive function calls a primitive function, the
`instantiate_symbols` pass will update the corresponding
`hidet.ir.primitives.func.PrimitiveFunctionRegistry.function` in-place
(I am not sure exactly how it's done, but this is what I observed),
adding symbol variables to its parameters. The primitive function pool
is a global variable, therefore this effect is cumulative across tuning
candidates. So while candidate 0 will have no problem, candidate 1 will
have two extra copies of symbol params, and so on, leading to compile
errors.

Since primitive functions do not need symbol vars, a quick fix is just
to not instantiate any symbols for them.

python/hidet/transforms/instantiate_symbols.py

@@ -15,6 +15,7 @@
 from hidet.ir.func import Function
 from hidet.ir.module import IRModule
 from hidet.ir.functors import IRRewriter
+from hidet.ir.primitives import is_primitive_function
 from hidet.ir.primitives.runtime import get_symbol_value
 from hidet.ir.stmt import LetStmt, LaunchKernelStmt
 from hidet.ir.tools import collect
@@ -59,6 +60,9 @@ def visit_Function(self, func: Function):
             else:
                 assert False
 
+        if is_primitive_function(func.name):
+            return func
+
         ordered_symbols: List[SymbolVar] = list(symbols)
         symbol_params: List[Var] = [Var(symbol.name, symbol.type) for symbol in ordered_symbols]
         self.func_symbols[func.name] = FuncSymbols(