LLVM  10.0.0svn
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1 //===- LICM.h - Loop Invariant Code Motion Pass -------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This pass performs loop invariant code motion, attempting to remove as much
10 // code from the body of a loop as possible. It does this by either hoisting
11 // code into the preheader block, or by sinking code to the exit blocks if it is
12 // safe. This pass also promotes must-aliased memory locations in the loop to
13 // live in registers, thus hoisting and sinking "invariant" loads and stores.
14 //
15 // This pass uses alias analysis for two purposes:
16 //
17 // 1. Moving loop invariant loads and calls out of loops. If we can determine
18 // that a load or call inside of a loop never aliases anything stored to,
19 // we can hoist it or sink it like any other instruction.
20 // 2. Scalar Promotion of Memory - If there is a store instruction inside of
21 // the loop, we try to move the store to happen AFTER the loop instead of
22 // inside of the loop. This can only happen if a few conditions are true:
23 // A. The pointer stored through is loop invariant
24 // B. There are no stores or loads in the loop which _may_ alias the
25 // pointer. There are no calls in the loop which mod/ref the pointer.
26 // If these conditions are true, we can promote the loads and stores in the
27 // loop of the pointer to use a temporary alloca'd variable. We then use
28 // the SSAUpdater to construct the appropriate SSA form for the value.
29 //
30 //===----------------------------------------------------------------------===//
35 #include "llvm/Analysis/LoopInfo.h"
36 #include "llvm/IR/PassManager.h"
39 namespace llvm {
41 extern cl::opt<unsigned> SetLicmMssaOptCap;
42 extern cl::opt<unsigned> SetLicmMssaNoAccForPromotionCap;
44 /// Performs Loop Invariant Code Motion Pass.
45 class LICMPass : public PassInfoMixin<LICMPass> {
46  unsigned LicmMssaOptCap;
47  unsigned LicmMssaNoAccForPromotionCap;
49 public:
51  : LicmMssaOptCap(SetLicmMssaOptCap),
52  LicmMssaNoAccForPromotionCap(SetLicmMssaNoAccForPromotionCap) {}
53  LICMPass(unsigned LicmMssaOptCap, unsigned LicmMssaNoAccForPromotionCap)
54  : LicmMssaOptCap(LicmMssaOptCap),
55  LicmMssaNoAccForPromotionCap(LicmMssaNoAccForPromotionCap) {}
58 };
59 } // end namespace llvm
This class represents lattice values for constants.
Definition: AllocatorList.h:23
Definition: LICM.h:50
This header provides classes for managing a pipeline of passes over loops in LLVM IR...
The adaptor from a function pass to a loop pass computes these analyses and makes them available to t...
Performs Loop Invariant Code Motion Pass.
Definition: LICM.h:45
A CRTP mix-in to automatically provide informational APIs needed for passes.
Definition: PassManager.h:373
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:154
cl::opt< unsigned > SetLicmMssaOptCap
PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM, LoopStandardAnalysisResults &AR, LPMUpdater &U)
Definition: LICM.cpp:277
This class provides an interface for updating the loop pass manager based on mutations to the loop ne...
cl::opt< unsigned > SetLicmMssaNoAccForPromotionCap
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:509
A container for analyses that lazily runs them and caches their results.
This header defines various interfaces for pass management in LLVM.
LICMPass(unsigned LicmMssaOptCap, unsigned LicmMssaNoAccForPromotionCap)
Definition: LICM.h:53