cmov self-refrencing.
Pointed out by Amjad Aboud in code review, test case minorly simplified
from the one he posted.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311267 91177308-0d34-0410-b5e6-96231b3b80d8
The primary thing that this accomplishes is to allow future re-use of
these routines in more contexts and clarify the behavior w.r.t. loops.
For example, if handling outer loops is desirable, doing so in
a inside-out order becomes straight forward because it walks the loop
nest itself (rather than walking the function's basic blocks) and
de-couples the CMOV rewriting from the loop structure as there isn't
actually anything loop-specific about this transformation.
This patch should be essentially a no-op. It potentially changes the
order in which we visit the inner loops, but otherwise should merely set
the stage for subsequent changes.
Differential Revision: https://reviews.llvm.org/D36783
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Resolved PR33954.
This patch contains two more constraints that aim to reduce the noise cases where we convert CMOV into branch for small gain, and end up spending more cycles due to overhead.
Differential Revision: https://reviews.llvm.org/D36081
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310352 91177308-0d34-0410-b5e6-96231b3b80d8
LLVM compiler recognizes opportunities to transform a branch into IR select instruction(s) - later it will be lowered into X86::CMOV instruction, assuming no other optimization eliminated the SelectInst.
However, it is not always profitable to emit X86::CMOV instruction. For example, branch is preferable over an X86::CMOV instruction when:
1. Branch is well predicted
2. Condition operand is expensive, compared to True-value and the False-value operands
In CodeGenPrepare pass there is a shallow optimization that tries to convert SelectInst into branch, but it is not enough.
This commit, implements machine optimization pass that converts X86::CMOV instruction(s) into branch, based on a conservative heuristic.
Differential Revision: https://reviews.llvm.org/D34769
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@308142 91177308-0d34-0410-b5e6-96231b3b80d8
Chandler Carruth