[LLVMdev] Question: Motivation of the semantics of the undefined value?

Chung-Kil Hur gil.hur at sf.snu.ac.kr
Mon Mar 16 08:49:19 PDT 2015

Dear LLVMdev,

We have a question regarding the semantics of the undefined value in LLVM

As far as we understand, in order to give a semantics to the undefined
value, the semantics of LLVM IR is generalized to a rather unusual
set-based semantics. More specifically, the notion of value in LLVM IR is
generalized to a set of values, rather than a single value. Then the
undefined value is simply defined as the set of all values.

Our question is simply why LLVM does not use the notion of trap
representation of C11 standard to represent the undefined value, rather
than using the set-based semantics.

We'd like to understand the motivation of the set-based semantics over the
trap representation.

Chung-Kil Hur, Steve Zdancewic & Viktor Vafeiadis.
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