[llvm-dev] How to deal with UNDEF SDNode?

陳韋任 via llvm-dev llvm-dev at lists.llvm.org
Fri Jun 23 05:48:10 PDT 2017

Hi Peter,

2017-06-23 1:13 GMT+08:00 Peter Lawrence via llvm-dev <
llvm-dev at lists.llvm.org>:

> Chenwj,
>              In ISD the UNDEF node (i.e. SDValue) is an "undefined value”,
> not “undefined behavior”, i.e. not scary!. You can think of it as an
> uninitialized / don’t-care register, or in a vector an uninitialized /
> don’t-care element.

So the UNDEF node corresponds to undefined value in LLVM LangRef [1], right?
And I can do whatever I want with those UNDEF nodes, right?


[1] http://llvm.org/docs/LangRef.html#undefined-values

Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
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