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Use VGPR_32 register class instead. These two register classes were identical and having separate classes was causing SIInstrInfo::isLegalOperands() to be overly conservative in some cases. This change is necessary to prevent future paches from missing a folding opportunity in fneg-fabs.ll. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225382 91177308-0d34-0410-b5e6-96231b3b80d8
337 lines
12 KiB
C++
337 lines
12 KiB
C++
//===-- SIFixSGPRCopies.cpp - Remove potential VGPR => SGPR copies --------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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/// \file
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/// Copies from VGPR to SGPR registers are illegal and the register coalescer
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/// will sometimes generate these illegal copies in situations like this:
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///
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/// Register Class <vsrc> is the union of <vgpr> and <sgpr>
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///
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/// BB0:
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/// %vreg0 <sgpr> = SCALAR_INST
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/// %vreg1 <vsrc> = COPY %vreg0 <sgpr>
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/// ...
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/// BRANCH %cond BB1, BB2
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/// BB1:
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/// %vreg2 <vgpr> = VECTOR_INST
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/// %vreg3 <vsrc> = COPY %vreg2 <vgpr>
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/// BB2:
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/// %vreg4 <vsrc> = PHI %vreg1 <vsrc>, <BB#0>, %vreg3 <vrsc>, <BB#1>
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/// %vreg5 <vgpr> = VECTOR_INST %vreg4 <vsrc>
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///
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///
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/// The coalescer will begin at BB0 and eliminate its copy, then the resulting
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/// code will look like this:
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///
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/// BB0:
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/// %vreg0 <sgpr> = SCALAR_INST
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/// ...
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/// BRANCH %cond BB1, BB2
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/// BB1:
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/// %vreg2 <vgpr> = VECTOR_INST
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/// %vreg3 <vsrc> = COPY %vreg2 <vgpr>
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/// BB2:
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/// %vreg4 <sgpr> = PHI %vreg0 <sgpr>, <BB#0>, %vreg3 <vsrc>, <BB#1>
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/// %vreg5 <vgpr> = VECTOR_INST %vreg4 <sgpr>
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///
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/// Now that the result of the PHI instruction is an SGPR, the register
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/// allocator is now forced to constrain the register class of %vreg3 to
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/// <sgpr> so we end up with final code like this:
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///
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/// BB0:
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/// %vreg0 <sgpr> = SCALAR_INST
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/// ...
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/// BRANCH %cond BB1, BB2
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/// BB1:
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/// %vreg2 <vgpr> = VECTOR_INST
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/// %vreg3 <sgpr> = COPY %vreg2 <vgpr>
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/// BB2:
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/// %vreg4 <sgpr> = PHI %vreg0 <sgpr>, <BB#0>, %vreg3 <sgpr>, <BB#1>
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/// %vreg5 <vgpr> = VECTOR_INST %vreg4 <sgpr>
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///
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/// Now this code contains an illegal copy from a VGPR to an SGPR.
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///
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/// In order to avoid this problem, this pass searches for PHI instructions
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/// which define a <vsrc> register and constrains its definition class to
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/// <vgpr> if the user of the PHI's definition register is a vector instruction.
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/// If the PHI's definition class is constrained to <vgpr> then the coalescer
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/// will be unable to perform the COPY removal from the above example which
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/// ultimately led to the creation of an illegal COPY.
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//===----------------------------------------------------------------------===//
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#include "AMDGPU.h"
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#include "AMDGPUSubtarget.h"
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#include "SIInstrInfo.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/MachineRegisterInfo.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetMachine.h"
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using namespace llvm;
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#define DEBUG_TYPE "sgpr-copies"
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namespace {
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class SIFixSGPRCopies : public MachineFunctionPass {
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private:
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static char ID;
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const TargetRegisterClass *inferRegClassFromUses(const SIRegisterInfo *TRI,
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const MachineRegisterInfo &MRI,
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unsigned Reg,
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unsigned SubReg) const;
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const TargetRegisterClass *inferRegClassFromDef(const SIRegisterInfo *TRI,
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const MachineRegisterInfo &MRI,
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unsigned Reg,
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unsigned SubReg) const;
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bool isVGPRToSGPRCopy(const MachineInstr &Copy, const SIRegisterInfo *TRI,
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const MachineRegisterInfo &MRI) const;
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public:
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SIFixSGPRCopies(TargetMachine &tm) : MachineFunctionPass(ID) { }
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bool runOnMachineFunction(MachineFunction &MF) override;
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const char *getPassName() const override {
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return "SI Fix SGPR copies";
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}
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};
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} // End anonymous namespace
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char SIFixSGPRCopies::ID = 0;
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FunctionPass *llvm::createSIFixSGPRCopiesPass(TargetMachine &tm) {
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return new SIFixSGPRCopies(tm);
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}
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static bool hasVGPROperands(const MachineInstr &MI, const SIRegisterInfo *TRI) {
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const MachineRegisterInfo &MRI = MI.getParent()->getParent()->getRegInfo();
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for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
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if (!MI.getOperand(i).isReg() ||
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!TargetRegisterInfo::isVirtualRegister(MI.getOperand(i).getReg()))
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continue;
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if (TRI->hasVGPRs(MRI.getRegClass(MI.getOperand(i).getReg())))
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return true;
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}
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return false;
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}
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/// This functions walks the use list of Reg until it finds an Instruction
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/// that isn't a COPY returns the register class of that instruction.
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/// \return The register defined by the first non-COPY instruction.
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const TargetRegisterClass *SIFixSGPRCopies::inferRegClassFromUses(
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const SIRegisterInfo *TRI,
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const MachineRegisterInfo &MRI,
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unsigned Reg,
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unsigned SubReg) const {
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const TargetRegisterClass *RC
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= TargetRegisterInfo::isVirtualRegister(Reg) ?
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MRI.getRegClass(Reg) :
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TRI->getRegClass(Reg);
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RC = TRI->getSubRegClass(RC, SubReg);
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for (MachineRegisterInfo::use_instr_iterator
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I = MRI.use_instr_begin(Reg), E = MRI.use_instr_end(); I != E; ++I) {
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switch (I->getOpcode()) {
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case AMDGPU::COPY:
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RC = TRI->getCommonSubClass(RC, inferRegClassFromUses(TRI, MRI,
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I->getOperand(0).getReg(),
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I->getOperand(0).getSubReg()));
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break;
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}
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}
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return RC;
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}
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const TargetRegisterClass *SIFixSGPRCopies::inferRegClassFromDef(
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const SIRegisterInfo *TRI,
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const MachineRegisterInfo &MRI,
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unsigned Reg,
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unsigned SubReg) const {
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if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
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const TargetRegisterClass *RC = TRI->getPhysRegClass(Reg);
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return TRI->getSubRegClass(RC, SubReg);
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}
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MachineInstr *Def = MRI.getVRegDef(Reg);
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if (Def->getOpcode() != AMDGPU::COPY) {
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return TRI->getSubRegClass(MRI.getRegClass(Reg), SubReg);
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}
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return inferRegClassFromDef(TRI, MRI, Def->getOperand(1).getReg(),
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Def->getOperand(1).getSubReg());
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}
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bool SIFixSGPRCopies::isVGPRToSGPRCopy(const MachineInstr &Copy,
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const SIRegisterInfo *TRI,
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const MachineRegisterInfo &MRI) const {
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unsigned DstReg = Copy.getOperand(0).getReg();
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unsigned SrcReg = Copy.getOperand(1).getReg();
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unsigned SrcSubReg = Copy.getOperand(1).getSubReg();
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const TargetRegisterClass *DstRC
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= TargetRegisterInfo::isVirtualRegister(DstReg) ?
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MRI.getRegClass(DstReg) :
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TRI->getRegClass(DstReg);
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const TargetRegisterClass *SrcRC;
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if (!TargetRegisterInfo::isVirtualRegister(SrcReg) ||
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DstRC == &AMDGPU::M0RegRegClass ||
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MRI.getRegClass(SrcReg) == &AMDGPU::VReg_1RegClass)
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return false;
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SrcRC = TRI->getSubRegClass(MRI.getRegClass(SrcReg), SrcSubReg);
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return TRI->isSGPRClass(DstRC) && TRI->hasVGPRs(SrcRC);
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}
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bool SIFixSGPRCopies::runOnMachineFunction(MachineFunction &MF) {
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MachineRegisterInfo &MRI = MF.getRegInfo();
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const SIRegisterInfo *TRI =
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static_cast<const SIRegisterInfo *>(MF.getSubtarget().getRegisterInfo());
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const SIInstrInfo *TII =
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static_cast<const SIInstrInfo *>(MF.getSubtarget().getInstrInfo());
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for (MachineFunction::iterator BI = MF.begin(), BE = MF.end();
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BI != BE; ++BI) {
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MachineBasicBlock &MBB = *BI;
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for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end();
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I != E; ++I) {
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MachineInstr &MI = *I;
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if (MI.getOpcode() == AMDGPU::COPY && isVGPRToSGPRCopy(MI, TRI, MRI)) {
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DEBUG(dbgs() << "Fixing VGPR -> SGPR copy:\n");
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DEBUG(MI.print(dbgs()));
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TII->moveToVALU(MI);
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}
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switch (MI.getOpcode()) {
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default: continue;
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case AMDGPU::PHI: {
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DEBUG(dbgs() << "Fixing PHI: " << MI);
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for (unsigned i = 1; i < MI.getNumOperands(); i += 2) {
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const MachineOperand &Op = MI.getOperand(i);
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unsigned Reg = Op.getReg();
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const TargetRegisterClass *RC
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= inferRegClassFromDef(TRI, MRI, Reg, Op.getSubReg());
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MRI.constrainRegClass(Op.getReg(), RC);
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}
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unsigned Reg = MI.getOperand(0).getReg();
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const TargetRegisterClass *RC = inferRegClassFromUses(TRI, MRI, Reg,
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MI.getOperand(0).getSubReg());
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if (TRI->getCommonSubClass(RC, &AMDGPU::VGPR_32RegClass)) {
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MRI.constrainRegClass(Reg, &AMDGPU::VGPR_32RegClass);
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}
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if (!TRI->isSGPRClass(MRI.getRegClass(Reg)))
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break;
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// If a PHI node defines an SGPR and any of its operands are VGPRs,
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// then we need to move it to the VALU.
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//
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// Also, if a PHI node defines an SGPR and has all SGPR operands
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// we must move it to the VALU, because the SGPR operands will
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// all end up being assigned the same register, which means
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// there is a potential for a conflict if different threads take
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// different control flow paths.
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//
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// For Example:
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//
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// sgpr0 = def;
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// ...
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// sgpr1 = def;
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// ...
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// sgpr2 = PHI sgpr0, sgpr1
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// use sgpr2;
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//
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// Will Become:
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//
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// sgpr2 = def;
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// ...
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// sgpr2 = def;
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// ...
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// use sgpr2
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//
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// FIXME: This is OK if the branching decision is made based on an
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// SGPR value.
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bool SGPRBranch = false;
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// The one exception to this rule is when one of the operands
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// is defined by a SI_BREAK, SI_IF_BREAK, or SI_ELSE_BREAK
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// instruction. In this case, there we know the program will
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// never enter the second block (the loop) without entering
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// the first block (where the condition is computed), so there
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// is no chance for values to be over-written.
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bool HasBreakDef = false;
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for (unsigned i = 1; i < MI.getNumOperands(); i+=2) {
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unsigned Reg = MI.getOperand(i).getReg();
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if (TRI->hasVGPRs(MRI.getRegClass(Reg))) {
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TII->moveToVALU(MI);
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break;
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}
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MachineInstr *DefInstr = MRI.getUniqueVRegDef(Reg);
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assert(DefInstr);
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switch(DefInstr->getOpcode()) {
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case AMDGPU::SI_BREAK:
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case AMDGPU::SI_IF_BREAK:
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case AMDGPU::SI_ELSE_BREAK:
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// If we see a PHI instruction that defines an SGPR, then that PHI
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// instruction has already been considered and should have
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// a *_BREAK as an operand.
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case AMDGPU::PHI:
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HasBreakDef = true;
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break;
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}
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}
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if (!SGPRBranch && !HasBreakDef)
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TII->moveToVALU(MI);
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break;
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}
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case AMDGPU::REG_SEQUENCE: {
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if (TRI->hasVGPRs(TII->getOpRegClass(MI, 0)) ||
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!hasVGPROperands(MI, TRI))
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continue;
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DEBUG(dbgs() << "Fixing REG_SEQUENCE: " << MI);
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TII->moveToVALU(MI);
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break;
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}
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case AMDGPU::INSERT_SUBREG: {
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const TargetRegisterClass *DstRC, *Src0RC, *Src1RC;
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DstRC = MRI.getRegClass(MI.getOperand(0).getReg());
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Src0RC = MRI.getRegClass(MI.getOperand(1).getReg());
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Src1RC = MRI.getRegClass(MI.getOperand(2).getReg());
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if (TRI->isSGPRClass(DstRC) &&
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(TRI->hasVGPRs(Src0RC) || TRI->hasVGPRs(Src1RC))) {
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DEBUG(dbgs() << " Fixing INSERT_SUBREG: " << MI);
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TII->moveToVALU(MI);
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}
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break;
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}
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}
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}
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}
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return true;
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}
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