[PATCH] [CodeGenPrepare.cpp] Feedback on changing logic when to convert select to branch

[Gerolf Hoflehner]

Hi grosbach, chandlerc, jmolloy,

The current logic in OptimizeSelectInst() converts a
select to a branch when the select is expensive (determined by a (sub-)target
specific flag) or the branch is cheaper (by some heuristic). The proposed change
enables the heuristic check to kick in even when the target specific flag
suggest any select is cheap and therefore should not be converted. Eventually we want good
heuristics when to prefer a branch over a select. Changing the condition when to
enable them is the first step doing so. At least on cyclone treating all selects
as 'cheap' results in regressions. I'm still evaluating the peformance impact of this change,
and look for feedback on the general direction.

http://reviews.llvm.org/D5998

Files:
  lib/CodeGen/CodeGenPrepare.cpp
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