lib/Target/PowerPC/PPCQPXLoadSplat.cpp

   1 //===----- PPCQPXLoadSplat.cpp - QPX Load Splat Simplification ------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // The QPX vector registers overlay the scalar floating-point registers, and
  11 // any scalar floating-point loads splat their value across all vector lanes.
  12 // Thus, if we have a scalar load followed by a splat, we can remove the splat
  13 // (i.e. replace the load with a load-and-splat pseudo instruction).
  14 //
  15 // This pass must run after anything that might do store-to-load forwarding.
  16 //
  17 //===----------------------------------------------------------------------===//
  18
  19 #include "PPC.h"
  20 #include "PPCInstrBuilder.h"
  21 #include "PPCInstrInfo.h"
  22 #include "llvm/ADT/SmallVector.h"
  23 #include "llvm/ADT/Statistic.h"
  24 #include "llvm/CodeGen/MachineFunctionPass.h"
  25 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  26 #include "llvm/Support/MathExtras.h"
  27 #include "llvm/Target/TargetMachine.h"
  28 using namespace llvm;
  29
  30 #define DEBUG_TYPE "ppc-qpx-load-splat"
  31
  32 STATISTIC(NumSimplified, "Number of QPX load splats simplified");
  33
  34 namespace llvm {
  35   void initializePPCQPXLoadSplatPass(PassRegistry&);
  36 }
  37
  38 namespace {
  39   struct PPCQPXLoadSplat : public MachineFunctionPass {
  40     static char ID;
  41     PPCQPXLoadSplat() : MachineFunctionPass(ID) {
  42       initializePPCQPXLoadSplatPass(*PassRegistry::getPassRegistry());
  43     }
  44
  45     bool runOnMachineFunction(MachineFunction &Fn) override;
  46
  47     StringRef getPassName() const override {
  48       return "PowerPC QPX Load Splat Simplification";
  49     }
  50   };
  51   char PPCQPXLoadSplat::ID = 0;
  52 }
  53
  54 INITIALIZE_PASS(PPCQPXLoadSplat, "ppc-qpx-load-splat",
  55                 "PowerPC QPX Load Splat Simplification",
  56                 false, false)
  57
  58 FunctionPass *llvm::createPPCQPXLoadSplatPass() {
  59   return new PPCQPXLoadSplat();
  60 }
  61
  62 bool PPCQPXLoadSplat::runOnMachineFunction(MachineFunction &MF) {
  63   if (skipFunction(MF.getFunction()))
  64     return false;
  65
  66   bool MadeChange = false;
  67   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
  68
  69   for (auto MFI = MF.begin(), MFIE = MF.end(); MFI != MFIE; ++MFI) {
  70     MachineBasicBlock *MBB = &*MFI;
  71     SmallVector<MachineInstr *, 4> Splats;
  72
  73     for (auto MBBI = MBB->rbegin(); MBBI != MBB->rend(); ++MBBI) {
  74       MachineInstr *MI = &*MBBI;
  75
  76       if (MI->hasUnmodeledSideEffects() || MI->isCall()) {
  77         Splats.clear();
  78         continue;
  79       }
  80
  81       // We're looking for a sequence like this:
  82       // %f0 = LFD 0, killed %x3, implicit-def %qf0; mem:LD8[%a](tbaa=!2)
  83       // %qf1 = QVESPLATI killed %qf0, 0, implicit %rm
  84
  85       for (auto SI = Splats.begin(); SI != Splats.end();) {
  86         MachineInstr *SMI = *SI;
  87         unsigned SplatReg = SMI->getOperand(0).getReg();
  88         unsigned SrcReg = SMI->getOperand(1).getReg();
  89
  90         if (MI->modifiesRegister(SrcReg, TRI)) {
  91           switch (MI->getOpcode()) {
  92           default:
  93             SI = Splats.erase(SI);
  94             continue;
  95           case PPC::LFS:
  96           case PPC::LFD:
  97           case PPC::LFSU:
  98           case PPC::LFDU:
  99           case PPC::LFSUX:
 100           case PPC::LFDUX:
 101           case PPC::LFSX:
 102           case PPC::LFDX:
 103           case PPC::LFIWAX:
 104           case PPC::LFIWZX:
 105             if (SplatReg != SrcReg) {
 106               // We need to change the load to define the scalar subregister of
 107               // the QPX splat source register.
 108               unsigned SubRegIndex =
 109                 TRI->getSubRegIndex(SrcReg, MI->getOperand(0).getReg());
 110               unsigned SplatSubReg = TRI->getSubReg(SplatReg, SubRegIndex);
 111
 112               // Substitute both the explicit defined register, and also the
 113               // implicit def of the containing QPX register.
 114               MI->getOperand(0).setReg(SplatSubReg);
 115               MI->substituteRegister(SrcReg, SplatReg, 0, *TRI);
 116             }
 117
 118             SI = Splats.erase(SI);
 119
 120             // If SMI is directly after MI, then MBBI's base iterator is
 121             // pointing at SMI.  Adjust MBBI around the call to erase SMI to
 122             // avoid invalidating MBBI.
 123             ++MBBI;
 124             SMI->eraseFromParent();
 125             --MBBI;
 126
 127             ++NumSimplified;
 128             MadeChange = true;
 129             continue;
 130           }
 131         }
 132
 133         // If this instruction defines the splat register, then we cannot move
 134         // the previous definition above it. If it reads from the splat
 135         // register, then it must already be alive from some previous
 136         // definition, and if the splat register is different from the source
 137         // register, then this definition must not be the load for which we're
 138         // searching.
 139         if (MI->modifiesRegister(SplatReg, TRI) ||
 140             (SrcReg != SplatReg &&
 141              MI->readsRegister(SplatReg, TRI))) {
 142           SI = Splats.erase(SI);
 143           continue;
 144         }
 145
 146         ++SI;
 147       }
 148
 149       if (MI->getOpcode() != PPC::QVESPLATI &&
 150           MI->getOpcode() != PPC::QVESPLATIs &&
 151           MI->getOpcode() != PPC::QVESPLATIb)
 152         continue;
 153       if (MI->getOperand(2).getImm() != 0)
 154         continue;
 155
 156       // If there are other uses of the scalar value after this, replacing
 157       // those uses might be non-trivial.
 158       if (!MI->getOperand(1).isKill())
 159         continue;
 160
 161       Splats.push_back(MI);
 162     }
 163   }
 164
 165   return MadeChange;
 166 }