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Summary: This extends the PeelingModuloScheduleExpander to generate prolog and epilog code, and correctly stitch uses through the prolog, kernel, epilog DAG. The key concept in this patch is to ensure that all transforms are *local*; only a function of a block and its immediate predecessor and successor. By defining the problem in this way we can inductively rewrite the entire DAG using only local knowledge that is easy to reason about. For example, we assume that all prologs and epilogs are near-perfect clones of the steady-state kernel. This means that if a block has an instruction that is predicated out, we can redirect all users of that instruction to that equivalent instruction in our immediate predecessor. As all blocks are clones, every instruction must have an equivalent in every other block. Similarly we can make the assumption by construction that if a value defined in a block is used outside that block, the only possible user is its immediate successors. We maintain this even for values that are used outside the loop by creating a limited form of LCSSA. This code isn't small, but it isn't complex. Enabled a bunch of testing from Hexagon. There are a couple of tests not enabled yet; I'm about 80% sure there isn't buggy codegen but the tests are checking for patterns that we don't produce. Those still need a bit more investigation. In the meantime we (Google) are happy with the code produced by this on our downstream SMS implementation, and believe it generates correct code. Subscribers: mgorny, hiraditya, jsji, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D68205 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373462 91177308-0d34-0410-b5e6-96231b3b80d8
42 lines
1.5 KiB
C++
42 lines
1.5 KiB
C++
//=- MachineLoopUtils.h - Helper functions for manipulating loops -*- 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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#ifndef LLVM_LIB_CODEGEN_MACHINELOOPUTILS_H
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#define LLVM_LIB_CODEGEN_MACHINELOOPUTILS_H
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namespace llvm {
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class MachineBasicBlock;
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class MachineRegisterInfo;
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class TargetInstrInfo;
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enum LoopPeelDirection {
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LPD_Front, ///< Peel the first iteration of the loop.
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LPD_Back ///< Peel the last iteration of the loop.
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};
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/// Peels a single block loop. Loop must have two successors, one of which
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/// must be itself. Similarly it must have two predecessors, one of which must
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/// be itself.
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///
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/// The loop block is copied and inserted into the CFG such that two copies of
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/// the loop follow on from each other. The copy is inserted either before or
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/// after the loop based on Direction.
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///
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/// Phis are updated and an unconditional branch inserted at the end of the
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/// clone so as to execute a single iteration.
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///
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/// The trip count of Loop is not updated.
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MachineBasicBlock *PeelSingleBlockLoop(LoopPeelDirection Direction,
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MachineBasicBlock *Loop,
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MachineRegisterInfo &MRI,
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const TargetInstrInfo *TII);
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} // namespace llvm
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#endif // LLVM_LIB_CODEGEN_MACHINELOOPUTILS_H
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