63 lines
2.8 KiB
C
63 lines
2.8 KiB
C
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//===- LICM.h - Loop Invariant Code Motion Pass -------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass performs loop invariant code motion, attempting to remove as much
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// code from the body of a loop as possible. It does this by either hoisting
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// code into the preheader block, or by sinking code to the exit blocks if it is
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// safe. This pass also promotes must-aliased memory locations in the loop to
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// live in registers, thus hoisting and sinking "invariant" loads and stores.
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//
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// This pass uses alias analysis for two purposes:
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//
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// 1. Moving loop invariant loads and calls out of loops. If we can determine
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// that a load or call inside of a loop never aliases anything stored to,
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// we can hoist it or sink it like any other instruction.
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// 2. Scalar Promotion of Memory - If there is a store instruction inside of
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// the loop, we try to move the store to happen AFTER the loop instead of
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// inside of the loop. This can only happen if a few conditions are true:
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// A. The pointer stored through is loop invariant
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// B. There are no stores or loads in the loop which _may_ alias the
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// pointer. There are no calls in the loop which mod/ref the pointer.
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// If these conditions are true, we can promote the loads and stores in the
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// loop of the pointer to use a temporary alloca'd variable. We then use
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// the SSAUpdater to construct the appropriate SSA form for the value.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_SCALAR_LICM_H
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#define LLVM_TRANSFORMS_SCALAR_LICM_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/Support/CommandLine.h"
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#include "llvm/Transforms/Scalar/LoopPassManager.h"
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namespace llvm {
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extern cl::opt<unsigned> SetLicmMssaOptCap;
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extern cl::opt<unsigned> SetLicmMssaNoAccForPromotionCap;
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/// Performs Loop Invariant Code Motion Pass.
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class LICMPass : public PassInfoMixin<LICMPass> {
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unsigned LicmMssaOptCap;
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unsigned LicmMssaNoAccForPromotionCap;
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public:
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LICMPass()
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: LicmMssaOptCap(SetLicmMssaOptCap),
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LicmMssaNoAccForPromotionCap(SetLicmMssaNoAccForPromotionCap) {}
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LICMPass(unsigned LicmMssaOptCap, unsigned LicmMssaNoAccForPromotionCap)
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: LicmMssaOptCap(LicmMssaOptCap),
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LicmMssaNoAccForPromotionCap(LicmMssaNoAccForPromotionCap) {}
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PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
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LoopStandardAnalysisResults &AR, LPMUpdater &U);
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};
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} // end namespace llvm
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#endif // LLVM_TRANSFORMS_SCALAR_LICM_H
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