[PATCH] CodeGenPrepare: Avoid and/or i1 in select conditions.

[Matthias Braun]

The commit message for this:

DAGCombine: Canonicalize select(and/or,x,y) depending on target.

This is based on the following equivalences:
select(C0 & C1, X, Y) <=> select(C0, select(C1, X, Y), Y)
select(C0 | C1, X, Y) <=> select(C0, X, select(C1, X, Y))

Many target cannot perform and/or on the CPU flags and therefore the
right side should be choosen to avoid materializign the i1 flags in an
integer register. If the target can perform this operation efficiently
we normalize to the left form.

Canonicalizing to nested selects has the problem that the and/or in the
conditions is only implcit afterwards, so this patch factors our bigger
parts of the and/or DAGCombiners so they can be applied to nested
selects as well.


REPOSITORY
  rL LLVM

http://reviews.llvm.org/D7622

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