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0e35152dbe
Like several other loop passes (the vectorizer, etc) this pass doesn't really fit the model of a loop pass. The critical distinction is that it isn't intended to be pipelined together with other loop passes. I plan to add some documentation to the loop pass manager to make this more clear on that side. LoopSink is also different because it doesn't really need a lot of the infrastructure of our loop passes. For example, if there aren't loop invariant instructions causing a preheader to exist, there is no need to form a preheader. It also doesn't need LCSSA because this pass is only involved in sinking invariant instructions from a preheader into the loop, not reasoning about live-outs. This allows some nice simplifications to the pass in the new PM where we can directly walk the loops once without restructuring them. Differential Revision: https://reviews.llvm.org/D28921 llvm-svn: 292589
41 lines
1.5 KiB
C++
41 lines
1.5 KiB
C++
//===- LoopSink.h - Loop Sink Pass ------------------------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file provides the interface for the Loop Sink pass.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_SCALAR_LOOPSINK_H
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#define LLVM_TRANSFORMS_SCALAR_LOOPSINK_H
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/IR/PassManager.h"
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#include "llvm/Transforms/Scalar/LoopPassManager.h"
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namespace llvm {
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/// A pass that does profile-guided sinking of instructions into loops.
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///
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/// This is a function pass as it shouldn't be composed into any kind of
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/// unified loop pass pipeline. The goal of it is to sink code into loops that
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/// is loop invariant but only required within the loop body when doing so
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/// reduces the global expected dynamic frequency with which it executes.
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/// A classic example is an extremely cold branch within a loop body.
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///
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/// We do this as a separate pass so that during normal optimization all
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/// invariant operations can be held outside the loop body to simplify
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/// fundamental analyses and transforms of the loop.
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class LoopSinkPass : public PassInfoMixin<LoopSinkPass> {
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public:
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PreservedAnalyses run(Function &F, FunctionAnalysisManager &FAM);
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};
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}
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#endif // LLVM_TRANSFORMS_SCALAR_LOOPSINK_H
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