http://llvm.org/bugs/show_bug.cgi?id=4920
Summary: Document undef semantics
Product: Documentation
Version: trunk
Platform: PC
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P2
Component: General docs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
LangRef should document undef better, some thoughts from a discussion on IRC:
x = undef
a = xor x, x
What is the value of x?
x = undef
i1 a = icmp x, 4
i2 b = icmp x,5
Both a and b can be true here
select undef,a,b -> either a or b
br undef, L1, L2 -> choose either br L1 or br L2, not unreachable
undef is a value in the range of the type, but it can change its value during
its lifetime.
Does using an 'undef' value destroy SSA properties of the program when you RAUW
a value with undef? (previously it was a single value, and optimizers could
rely on this, after the replace it can become different values at different
points).
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