[TIR] Make syntax of AST nodes different than ops

[junrushao]

Motivation example: in the current TVMScript, the snippet below:

@T.prim_func
def func(...):
    A = T.match_buffer[(128 * 128), "float32"]
                       ^^^^^^^^^^^

is actually different from this one:

@T.prim_func
def func(...):
    A = T.match_buffer[(16384, ), "float32"]
                       ^^^^^^^^^
    ...

This is because 128 * 128 is not immediately constant-folded into 16384, but becomes an AST node: T.Mul(128, 128). This can be quite error-prone if not used carefully.

As part of effort of more formal TIR semantics, we want to more explicitly differentiate TIR AST nodes (defined in tir/expr.h) and TIR ops (defined in tir/op.h). The naming convention is that:

• Lowercased methods, for example, tvm.tir.mul or operator *, means an TIR op, which will be eagerly constant-folded, i.e. mul(1, 2) returns 3 immediately rather than creating an AST node.
• Capitalized callable, for example, Mul, means creating an AST node without constant folding.

This PR makes this behavior more explictly by printing T.Mul(a, b) directly when a and b are both constants, rather than sugaring it into mul(a. b) or a * b, so that the difference between an op and an AST node is clarified.

Co-authored-by: Yaxing Cai <caiyaxing666@gmail.com>

[tvm-bot]

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• cc @Hzfengsy _{See #10317 for details}
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[Hzfengsy]

LGTM