[GitHub] [tvm] Johnson9009 commented on pull request #8706: [TIR] enhance tir signed-unsigned cast

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Johnson9009 commented on pull request #8706:
URL: https://github.com/apache/tvm/pull/8706#issuecomment-898280034


   @ganler @YuchenJin @tqchen I happens to file a PR relevant to this change, after reading all of your preceding discussing, I think there maybe have something not clear.
   
   From reading the PR, I found, for the test case here `tir.const(1, "int32").__eq__(tir.const(1, "uint1"))`, the old behavior of BinaryOpMatchTypes is `int32 == uint1  -> int32 == int32(uint1)`, it is exactly same with the job that this PR does.
   
   Then I feel it is strange why this PR and my own PR can make `assert tir.const(1) == tir.const(True)` work, after debug it step-by-step I found the reason is the function we use "cast" instead the "tir::Cast" used by "SimpleCast".
   
   https://github.com/apache/tvm/blob/a06863ac9406c027b29f346fb6177268f612912d/src/tir/op/op.cc#L273-L284
   
   We can see it is the logic around line 279 that eliminate the CastNode, so the function `cast` is do some constant fold optimization.
   
   > Hi @ganler, Overall LGTM! Thanks for elaborating on the issue and implementing the fix!
   > 
   > One question is that whether we want to also make `assert tir.const(1, "uint2") == tir.const(1, "int2")` work? I think since `lhs` and `rhs` have the same bits, `SimpleCast` will be applied to both sides, but the same error throws.
   
   @YuchenJin For the scenario that unsigned and signed integer have the same width, I think we should consistent with C standard (e.g., "int32 + uint32" -> "uint32(int32) + uint32") instead of current logic "int32 + uint32" -> "int32 + int32(uint32)", please have a look of my PR #8733, we implement a new AI chip backend of TVM, now we meet this issue, we need make a pass to change the implicit conversion consistent with C standard. 
   


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