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      1 //===-- ARMHazardRecognizer.cpp - ARM postra hazard recognizer ------------===//
      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 #include "ARMHazardRecognizer.h"
     11 #include "ARMBaseInstrInfo.h"
     12 #include "ARMBaseRegisterInfo.h"
     13 #include "ARMSubtarget.h"
     14 #include "llvm/CodeGen/MachineInstr.h"
     15 #include "llvm/CodeGen/ScheduleDAG.h"
     16 #include "llvm/Target/TargetRegisterInfo.h"
     17 using namespace llvm;
     18 
     19 static bool hasRAWHazard(MachineInstr *DefMI, MachineInstr *MI,
     20                          const TargetRegisterInfo &TRI) {
     21   // FIXME: Detect integer instructions properly.
     22   const MCInstrDesc &MCID = MI->getDesc();
     23   unsigned Domain = MCID.TSFlags & ARMII::DomainMask;
     24   if (MI->mayStore())
     25     return false;
     26   unsigned Opcode = MCID.getOpcode();
     27   if (Opcode == ARM::VMOVRS || Opcode == ARM::VMOVRRD)
     28     return false;
     29   if ((Domain & ARMII::DomainVFP) || (Domain & ARMII::DomainNEON))
     30     return MI->readsRegister(DefMI->getOperand(0).getReg(), &TRI);
     31   return false;
     32 }
     33 
     34 ScheduleHazardRecognizer::HazardType
     35 ARMHazardRecognizer::getHazardType(SUnit *SU, int Stalls) {
     36   assert(Stalls == 0 && "ARM hazards don't support scoreboard lookahead");
     37 
     38   MachineInstr *MI = SU->getInstr();
     39 
     40   if (!MI->isDebugValue()) {
     41     // Look for special VMLA / VMLS hazards. A VMUL / VADD / VSUB following
     42     // a VMLA / VMLS will cause 4 cycle stall.
     43     const MCInstrDesc &MCID = MI->getDesc();
     44     if (LastMI && (MCID.TSFlags & ARMII::DomainMask) != ARMII::DomainGeneral) {
     45       MachineInstr *DefMI = LastMI;
     46       const MCInstrDesc &LastMCID = LastMI->getDesc();
     47       const TargetMachine &TM =
     48         MI->getParent()->getParent()->getTarget();
     49       const ARMBaseInstrInfo &TII =
     50         *static_cast<const ARMBaseInstrInfo*>(TM.getInstrInfo());
     51 
     52       // Skip over one non-VFP / NEON instruction.
     53       if (!LastMI->isBarrier() &&
     54           // On A9, AGU and NEON/FPU are muxed.
     55           !(TII.getSubtarget().isLikeA9() &&
     56             (LastMI->mayLoad() || LastMI->mayStore())) &&
     57           (LastMCID.TSFlags & ARMII::DomainMask) == ARMII::DomainGeneral) {
     58         MachineBasicBlock::iterator I = LastMI;
     59         if (I != LastMI->getParent()->begin()) {
     60           I = llvm::prior(I);
     61           DefMI = &*I;
     62         }
     63       }
     64 
     65       if (TII.isFpMLxInstruction(DefMI->getOpcode()) &&
     66           (TII.canCauseFpMLxStall(MI->getOpcode()) ||
     67            hasRAWHazard(DefMI, MI, TII.getRegisterInfo()))) {
     68         // Try to schedule another instruction for the next 4 cycles.
     69         if (FpMLxStalls == 0)
     70           FpMLxStalls = 4;
     71         return Hazard;
     72       }
     73     }
     74   }
     75 
     76   return ScoreboardHazardRecognizer::getHazardType(SU, Stalls);
     77 }
     78 
     79 void ARMHazardRecognizer::Reset() {
     80   LastMI = 0;
     81   FpMLxStalls = 0;
     82   ScoreboardHazardRecognizer::Reset();
     83 }
     84 
     85 void ARMHazardRecognizer::EmitInstruction(SUnit *SU) {
     86   MachineInstr *MI = SU->getInstr();
     87   if (!MI->isDebugValue()) {
     88     LastMI = MI;
     89     FpMLxStalls = 0;
     90   }
     91 
     92   ScoreboardHazardRecognizer::EmitInstruction(SU);
     93 }
     94 
     95 void ARMHazardRecognizer::AdvanceCycle() {
     96   if (FpMLxStalls && --FpMLxStalls == 0)
     97     // Stalled for 4 cycles but still can't schedule any other instructions.
     98     LastMI = 0;
     99   ScoreboardHazardRecognizer::AdvanceCycle();
    100 }
    101 
    102 void ARMHazardRecognizer::RecedeCycle() {
    103   llvm_unreachable("reverse ARM hazard checking unsupported");
    104 }
    105