mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-11-23 03:02:36 +01:00
acbb48020d
The patch modifies HexagonVectorLoopCarriedReuse pass to make it compatible with both Legacy Pass Manager through HexagonVectorLoopCarriedReuseLegacyPass and with New Pass Manager through HexagonVectorLoopCarriedReusePass. Reviewed By: pzheng Differential Revision: https://reviews.llvm.org/D86955
140 lines
4.4 KiB
C++
140 lines
4.4 KiB
C++
//===- HexagonVectorLoopCarriedReuse.h ------------------------------------===//
|
|
//
|
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
|
|
// See https://llvm.org/LICENSE.txt for license information.
|
|
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This pass removes the computation of provably redundant expressions that have
|
|
// been computed earlier in a previous iteration. It relies on the use of PHIs
|
|
// to identify loop carried dependences. This is scalar replacement for vector
|
|
// types.
|
|
//
|
|
//-----------------------------------------------------------------------------
|
|
// Motivation: Consider the case where we have the following loop structure.
|
|
//
|
|
// Loop:
|
|
// t0 = a[i];
|
|
// t1 = f(t0);
|
|
// t2 = g(t1);
|
|
// ...
|
|
// t3 = a[i+1];
|
|
// t4 = f(t3);
|
|
// t5 = g(t4);
|
|
// t6 = op(t2, t5)
|
|
// cond_branch <Loop>
|
|
//
|
|
// This can be converted to
|
|
// t00 = a[0];
|
|
// t10 = f(t00);
|
|
// t20 = g(t10);
|
|
// Loop:
|
|
// t2 = t20;
|
|
// t3 = a[i+1];
|
|
// t4 = f(t3);
|
|
// t5 = g(t4);
|
|
// t6 = op(t2, t5)
|
|
// t20 = t5
|
|
// cond_branch <Loop>
|
|
//
|
|
// SROA does a good job of reusing a[i+1] as a[i] in the next iteration.
|
|
// Such a loop comes to this pass in the following form.
|
|
//
|
|
// LoopPreheader:
|
|
// X0 = a[0];
|
|
// Loop:
|
|
// X2 = PHI<(X0, LoopPreheader), (X1, Loop)>
|
|
// t1 = f(X2) <-- I1
|
|
// t2 = g(t1)
|
|
// ...
|
|
// X1 = a[i+1]
|
|
// t4 = f(X1) <-- I2
|
|
// t5 = g(t4)
|
|
// t6 = op(t2, t5)
|
|
// cond_branch <Loop>
|
|
//
|
|
// In this pass, we look for PHIs such as X2 whose incoming values come only
|
|
// from the Loop Preheader and over the backedge and additionaly, both these
|
|
// values are the results of the same operation in terms of opcode. We call such
|
|
// a PHI node a dependence chain or DepChain. In this case, the dependence of X2
|
|
// over X1 is carried over only one iteration and so the DepChain is only one
|
|
// PHI node long.
|
|
//
|
|
// Then, we traverse the uses of the PHI (X2) and the uses of the value of the
|
|
// PHI coming over the backedge (X1). We stop at the first pair of such users
|
|
// I1 (of X2) and I2 (of X1) that meet the following conditions.
|
|
// 1. I1 and I2 are the same operation, but with different operands.
|
|
// 2. X2 and X1 are used at the same operand number in the two instructions.
|
|
// 3. All other operands Op1 of I1 and Op2 of I2 are also such that there is a
|
|
// a DepChain from Op1 to Op2 of the same length as that between X2 and X1.
|
|
//
|
|
// We then make the following transformation
|
|
// LoopPreheader:
|
|
// X0 = a[0];
|
|
// Y0 = f(X0);
|
|
// Loop:
|
|
// X2 = PHI<(X0, LoopPreheader), (X1, Loop)>
|
|
// Y2 = PHI<(Y0, LoopPreheader), (t4, Loop)>
|
|
// t1 = f(X2) <-- Will be removed by DCE.
|
|
// t2 = g(Y2)
|
|
// ...
|
|
// X1 = a[i+1]
|
|
// t4 = f(X1)
|
|
// t5 = g(t4)
|
|
// t6 = op(t2, t5)
|
|
// cond_branch <Loop>
|
|
//
|
|
// We proceed until we cannot find any more such instructions I1 and I2.
|
|
//
|
|
// --- DepChains & Loop carried dependences ---
|
|
// Consider a single basic block loop such as
|
|
//
|
|
// LoopPreheader:
|
|
// X0 = ...
|
|
// Y0 = ...
|
|
// Loop:
|
|
// X2 = PHI<(X0, LoopPreheader), (X1, Loop)>
|
|
// Y2 = PHI<(Y0, LoopPreheader), (X2, Loop)>
|
|
// ...
|
|
// X1 = ...
|
|
// ...
|
|
// cond_branch <Loop>
|
|
//
|
|
// Then there is a dependence between X2 and X1 that goes back one iteration,
|
|
// i.e. X1 is used as X2 in the very next iteration. We represent this as a
|
|
// DepChain from X2 to X1 (X2->X1).
|
|
// Similarly, there is a dependence between Y2 and X1 that goes back two
|
|
// iterations. X1 is used as Y2 two iterations after it is computed. This is
|
|
// represented by a DepChain as (Y2->X2->X1).
|
|
//
|
|
// A DepChain has the following properties.
|
|
// 1. Num of edges in DepChain = Number of Instructions in DepChain = Number of
|
|
// iterations of carried dependence + 1.
|
|
// 2. All instructions in the DepChain except the last are PHIs.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#ifndef LLVM_LIB_TARGET_HEXAGON_HEXAGONVLCR_H
|
|
#define LLVM_LIB_TARGET_HEXAGON_HEXAGONVLCR_H
|
|
|
|
#include "llvm/Transforms/Scalar/LoopPassManager.h"
|
|
|
|
namespace llvm {
|
|
|
|
class Loop;
|
|
|
|
/// Hexagon Vector Loop Carried Reuse Pass
|
|
struct HexagonVectorLoopCarriedReusePass
|
|
: public PassInfoMixin<HexagonVectorLoopCarriedReusePass> {
|
|
HexagonVectorLoopCarriedReusePass() {}
|
|
|
|
/// Run pass over the Loop.
|
|
PreservedAnalyses run(Loop &L, LoopAnalysisManager &LAM,
|
|
LoopStandardAnalysisResults &AR, LPMUpdater &U);
|
|
};
|
|
|
|
} // end namespace llvm
|
|
|
|
#endif // LLVM_LIB_TARGET_HEXAGON_HEXAGONVLCR_H
|