[llvm-commits] [Review request] Have Correlated Value Propagation handle instruction operands.

[Frits van Bommel]

This patch teaches -correlated-propagation to check whether LVI knows
instruction operands to be constant, and if so to replace them. It
also adds a call to SimplifyInstruction afterwards so that the special
handling of some instructions (select, load, store) is no longer
needed.

This fixes the -correlated-propagation problem mentioned in comment 1
of PR 9004[1] and is an alternative implementation of "A small pass to
constant fold branch conditions in destination blocks"[2] which
integrates with the existing pass as Duncan suggested.
Since it leverages LVI, this also handles the 'if (x == 0) use(x)'
case mentioned in that post as well as the 'x > 10' followed by 'x >
5' case I mentioned in a follow-up (and doesn't need a domtree).

It passes 'make check-all'.


[1]: http://llvm.org/bugs/show_bug.cgi?id=9004
[2]: http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-February/037884.html
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