【CINN】Add TryFuseSameSource func for IterExpr.

[liuruyan]

PR Category

CINN

PR Types

New features

Description

1. Change Expr to IndexExpr in func of IterExpr.
2. Add TryFuseSameSource func for simplify the iter when comes from same source.

(i_j_k_fused / 16 / 2 * 32 + i_j_k_fused / 16 % 2 * 16 +  i_j_k_fused % 16) / 8
=====>
i_j_k_fused / 8

3. Add comment for TryFuse and TryFuseSameSource.
4. Add Hash func for IndexExpr.

Pcard-67164

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[zyfncg]

这两个函数的注释加到头文件里，具体说明下分别在什么情况使用

[liuruyan]

收到，下一个PR中将进行调整。