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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 MachineFunction *MF = MI->getParent()->getParent();
     48       const ARMBaseInstrInfo &TII = *static_cast<const ARMBaseInstrInfo *>(
     49                                         MF->getSubtarget().getInstrInfo());
     50 
     51       // Skip over one non-VFP / NEON instruction.
     52       if (!LastMI->isBarrier() &&
     53           // On A9, AGU and NEON/FPU are muxed.
     54           !(TII.getSubtarget().isLikeA9() && LastMI->mayLoadOrStore()) &&
     55           (LastMCID.TSFlags & ARMII::DomainMask) == ARMII::DomainGeneral) {
     56         MachineBasicBlock::iterator I = LastMI;
     57         if (I != LastMI->getParent()->begin()) {
     58           I = std::prev(I);
     59           DefMI = &*I;
     60         }
     61       }
     62 
     63       if (TII.isFpMLxInstruction(DefMI->getOpcode()) &&
     64           (TII.canCauseFpMLxStall(MI->getOpcode()) ||
     65            hasRAWHazard(DefMI, MI, TII.getRegisterInfo()))) {
     66         // Try to schedule another instruction for the next 4 cycles.
     67         if (FpMLxStalls == 0)
     68           FpMLxStalls = 4;
     69         return Hazard;
     70       }
     71     }
     72   }
     73 
     74   return ScoreboardHazardRecognizer::getHazardType(SU, Stalls);
     75 }
     76 
     77 void ARMHazardRecognizer::Reset() {
     78   LastMI = nullptr;
     79   FpMLxStalls = 0;
     80   ScoreboardHazardRecognizer::Reset();
     81 }
     82 
     83 void ARMHazardRecognizer::EmitInstruction(SUnit *SU) {
     84   MachineInstr *MI = SU->getInstr();
     85   if (!MI->isDebugValue()) {
     86     LastMI = MI;
     87     FpMLxStalls = 0;
     88   }
     89 
     90   ScoreboardHazardRecognizer::EmitInstruction(SU);
     91 }
     92 
     93 void ARMHazardRecognizer::AdvanceCycle() {
     94   if (FpMLxStalls && --FpMLxStalls == 0)
     95     // Stalled for 4 cycles but still can't schedule any other instructions.
     96     LastMI = nullptr;
     97   ScoreboardHazardRecognizer::AdvanceCycle();
     98 }
     99 
    100 void ARMHazardRecognizer::RecedeCycle() {
    101   llvm_unreachable("reverse ARM hazard checking unsupported");
    102 }
    103