[llvm-commits] [Patch] Make GlobalOpt conservative with TLS vars (PR14309, 3.2-blocker)

[Hans Wennborg]

Hi all,

The attached patch takes a stab at fixing PR14309 which was marked as
a 3.2-blocker.

For global variables which get the same value stored into them
everywhere, GlobalOpt will replace them with a constant. The problem
is that a thread-local GlobalVariable looks like one value, but is
different between threads.

My patch introduces Constant::isThreadDependent() which returns true
for thread-local variables and constants which depend on them (e.g. a
GEP into a thread-local array), and teaches GlobalOpt not to track
such values.

Please take a look!

Also, if anyone thinks there are more passes which assume that
thread-local GlobalVariables have the same value everywhere, please
let me know.

Thanks,
Hans
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