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

陳韋任 via llvm-dev llvm-dev at lists.llvm.org
Thu Jun 22 06:21:09 PDT 2017

Hi All,

  The comment of UNDEF in ISDOpcodes.h [1] is pretty simple,

      /// UNDEF - An undefined node.

The name make me think of C undefined behavior, which is ... scary. But I
also see there are
APIs like isBuildVectorAllOnes, isBuildVectorAllZeros, ... etc, seems UNDEF
just can be any
value and we don't care about what it is. The most case I see UNDEF is in
VECTOR_SHUFFLE, ... etc. I would like to know usually how we deal with
those UNDEF nodes?


[1] http://llvm.org/doxygen/ISDOpcodes_8h_source.html


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