lib/Target/PowerPC/PPCQPXLoadSplat.cpp

   1 //===----- PPCQPXLoadSplat.cpp - QPX Load Splat Simplification ------------===//
   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 // The QPX vector registers overlay the scalar floating-point registers, and
  10 // any scalar floating-point loads splat their value across all vector lanes.
  11 // Thus, if we have a scalar load followed by a splat, we can remove the splat
  12 // (i.e. replace the load with a load-and-splat pseudo instruction).
  13 //
  14 // This pass must run after anything that might do store-to-load forwarding.
  15 //
  16 //===----------------------------------------------------------------------===//
  17
  18 #include "PPC.h"
  19 #include "PPCInstrBuilder.h"
  20 #include "PPCInstrInfo.h"
  21 #include "llvm/ADT/SmallVector.h"
  22 #include "llvm/ADT/Statistic.h"
  23 #include "llvm/CodeGen/MachineFunctionPass.h"
  24 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  25 #include "llvm/Support/MathExtras.h"
  26 #include "llvm/Target/TargetMachine.h"
  27 using namespace llvm;
  28
  29 #define DEBUG_TYPE "ppc-qpx-load-splat"
  30
  31 STATISTIC(NumSimplified, "Number of QPX load splats simplified");
  32
  33 namespace {
  34   struct PPCQPXLoadSplat : public MachineFunctionPass {
  35     static char ID;
  36     PPCQPXLoadSplat() : MachineFunctionPass(ID) {
  37       initializePPCQPXLoadSplatPass(*PassRegistry::getPassRegistry());
  38     }
  39
  40     bool runOnMachineFunction(MachineFunction &Fn) override;
  41
  42     StringRef getPassName() const override {
  43       return "PowerPC QPX Load Splat Simplification";
  44     }
  45   };
  46   char PPCQPXLoadSplat::ID = 0;
  47 }
  48
  49 INITIALIZE_PASS(PPCQPXLoadSplat, "ppc-qpx-load-splat",
  50                 "PowerPC QPX Load Splat Simplification",
  51                 false, false)
  52
  53 FunctionPass *llvm::createPPCQPXLoadSplatPass() {
  54   return new PPCQPXLoadSplat();
  55 }
  56
  57 bool PPCQPXLoadSplat::runOnMachineFunction(MachineFunction &MF) {
  58   if (skipFunction(MF.getFunction()))
  59     return false;
  60
  61   bool MadeChange = false;
  62   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
  63
  64   for (auto MFI = MF.begin(), MFIE = MF.end(); MFI != MFIE; ++MFI) {
  65     MachineBasicBlock *MBB = &*MFI;
  66     SmallVector<MachineInstr *, 4> Splats;
  67
  68     for (auto MBBI = MBB->rbegin(); MBBI != MBB->rend(); ++MBBI) {
  69       MachineInstr *MI = &*MBBI;
  70
  71       if (MI->hasUnmodeledSideEffects() || MI->isCall()) {
  72         Splats.clear();
  73         continue;
  74       }
  75
  76       // We're looking for a sequence like this:
  77       // %f0 = LFD 0, killed %x3, implicit-def %qf0; mem:LD8[%a](tbaa=!2)
  78       // %qf1 = QVESPLATI killed %qf0, 0, implicit %rm
  79
  80       for (auto SI = Splats.begin(); SI != Splats.end();) {
  81         MachineInstr *SMI = *SI;
  82         unsigned SplatReg = SMI->getOperand(0).getReg();
  83         unsigned SrcReg = SMI->getOperand(1).getReg();
  84
  85         if (MI->modifiesRegister(SrcReg, TRI)) {
  86           switch (MI->getOpcode()) {
  87           default:
  88             SI = Splats.erase(SI);
  89             continue;
  90           case PPC::LFS:
  91           case PPC::LFD:
  92           case PPC::LFSU:
  93           case PPC::LFDU:
  94           case PPC::LFSUX:
  95           case PPC::LFDUX:
  96           case PPC::LFSX:
  97           case PPC::LFDX:
  98           case PPC::LFIWAX:
  99           case PPC::LFIWZX:
 100             if (SplatReg != SrcReg) {
 101               // We need to change the load to define the scalar subregister of
 102               // the QPX splat source register.
 103               unsigned SubRegIndex =
 104                 TRI->getSubRegIndex(SrcReg, MI->getOperand(0).getReg());
 105               unsigned SplatSubReg = TRI->getSubReg(SplatReg, SubRegIndex);
 106
 107               // Substitute both the explicit defined register, and also the
 108               // implicit def of the containing QPX register.
 109               MI->getOperand(0).setReg(SplatSubReg);
 110               MI->substituteRegister(SrcReg, SplatReg, 0, *TRI);
 111             }
 112
 113             SI = Splats.erase(SI);
 114
 115             // If SMI is directly after MI, then MBBI's base iterator is
 116             // pointing at SMI.  Adjust MBBI around the call to erase SMI to
 117             // avoid invalidating MBBI.
 118             ++MBBI;
 119             SMI->eraseFromParent();
 120             --MBBI;
 121
 122             ++NumSimplified;
 123             MadeChange = true;
 124             continue;
 125           }
 126         }
 127
 128         // If this instruction defines the splat register, then we cannot move
 129         // the previous definition above it. If it reads from the splat
 130         // register, then it must already be alive from some previous
 131         // definition, and if the splat register is different from the source
 132         // register, then this definition must not be the load for which we're
 133         // searching.
 134         if (MI->modifiesRegister(SplatReg, TRI) ||
 135             (SrcReg != SplatReg &&
 136              MI->readsRegister(SplatReg, TRI))) {
 137           SI = Splats.erase(SI);
 138           continue;
 139         }
 140
 141         ++SI;
 142       }
 143
 144       if (MI->getOpcode() != PPC::QVESPLATI &&
 145           MI->getOpcode() != PPC::QVESPLATIs &&
 146           MI->getOpcode() != PPC::QVESPLATIb)
 147         continue;
 148       if (MI->getOperand(2).getImm() != 0)
 149         continue;
 150
 151       // If there are other uses of the scalar value after this, replacing
 152       // those uses might be non-trivial.
 153       if (!MI->getOperand(1).isKill())
 154         continue;
 155
 156       Splats.push_back(MI);
 157     }
 158   }
 159
 160   return MadeChange;
 161 }