[schedule] Improve ceil_divide in tile/split #3842
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@tqchen I added arg bind support for the case. please review again. |
src/pass/arg_binder.cc
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| @@ -46,25 +47,41 @@ void BinderAddAssert(Expr cond, | |||
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| } | |||
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| // Deal with things like arg = 8 * M | |||
| // TODO(Yizhi Liu): make it more general | |||
| std::pair<Expr, Expr> TryExtractVariable(const Expr& arg, const Expr& value) { | |||
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Please comment about an example use-case.
This logic deals with an additional constraint like 8 * arg = value, and we would like to know what is the example application. Because normally, this will generate a constraint instead and the simplifier should be able to simplify the constraint. So we won't need this logic.
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without the fix, tvm will complain things like "TVMError: Not all Vars are passed in api_args: 'M' 'K' 'N' does not appear in api_args"
The example use-case is op computation for mxnet. To get decent performance for unknown shape (during compile time), we generate multiple kernels for one operator, and dispatch according to the shape during runtime. However, if the shape is pure symbolic, tiling/splitting has to generate if-else, which hurts the performance. One idea is to "hint" tvm, say, this shape can be divided by 8, pls don't generate if-else for tile size 2/4/8. This is where 8*M comes from.
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I see, i think we could use better expressions for such kind of hint. Your proposal is interesting.
We could also use alternatives to resolve this problem, in particular, we can do something like
AssertExpr(x, x % 8 == 0). Given this change affects more of the perf, can be separate it out from this PR?
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do you mean remove the second commit (support arithmetic size in codegen) from this PR and merge the first one (Improve ceil_divide in tile/split) for now?
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Yes, we can use a second PR for that
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Thanks @yzhliu |
https://discuss.tvm.ai/t/codegen-codegen-with-minimum-if-condition/3838
@tqchen @icemelon9