[llvm] r329673 - [x86] Model the direction flag (DF) separately from the rest of EFLAGS.

Hans Wennborg via llvm-commits llvm-commits at lists.llvm.org
Tue Apr 10 08:22:28 PDT 2018


We're hitting an assert in Chromium due to this, see https://crbug.com/831158

I've started looking but have to head out now, so maybe you or Nico
will get to it before I do.

On Tue, Apr 10, 2018 at 8:40 AM, Chandler Carruth via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: chandlerc
> Date: Mon Apr  9 23:40:51 2018
> New Revision: 329673
>
> URL: http://llvm.org/viewvc/llvm-project?rev=329673&view=rev
> Log:
> [x86] Model the direction flag (DF) separately from the rest of EFLAGS.
>
> This cleans up a number of operations that only claimed te use EFLAGS
> due to using DF. But no instructions which we think of us setting EFLAGS
> actually modify DF (other than things like popf) and so this needlessly
> creates uses of EFLAGS that aren't really there.
>
> In fact, DF is so restrictive it is pretty easy to model. Only STD, CLD,
> and the whole-flags writes (WRFLAGS and POPF) need to model this.
>
> I've also somewhat cleaned up some of the flag management instruction
> definitions to be in the correct .td file.
>
> Adding this extra register also uncovered a failure to use the correct
> datatype to hold X86 registers, and I've corrected that as necessary
> here.
>
> Differential Revision: https://reviews.llvm.org/D45154
>
> Modified:
>     llvm/trunk/lib/Target/X86/Disassembler/X86Disassembler.cpp
>     llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
>     llvm/trunk/lib/Target/X86/X86InstrCompiler.td
>     llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
>     llvm/trunk/lib/Target/X86/X86InstrInfo.td
>     llvm/trunk/lib/Target/X86/X86InstrSystem.td
>     llvm/trunk/lib/Target/X86/X86RegisterInfo.td
>     llvm/trunk/test/CodeGen/X86/ipra-reg-usage.ll
>
> Modified: llvm/trunk/lib/Target/X86/Disassembler/X86Disassembler.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/Disassembler/X86Disassembler.cpp?rev=329673&r1=329672&r2=329673&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/Disassembler/X86Disassembler.cpp (original)
> +++ llvm/trunk/lib/Target/X86/Disassembler/X86Disassembler.cpp Mon Apr  9 23:40:51 2018
> @@ -265,13 +265,10 @@ MCDisassembler::DecodeStatus X86GenericD
>  /// @param reg        - The Reg to append.
>  static void translateRegister(MCInst &mcInst, Reg reg) {
>  #define ENTRY(x) X86::x,
> -  uint8_t llvmRegnums[] = {
> -    ALL_REGS
> -    0
> -  };
> +  static constexpr MCPhysReg llvmRegnums[] = {ALL_REGS};
>  #undef ENTRY
>
> -  uint8_t llvmRegnum = llvmRegnums[reg];
> +  MCPhysReg llvmRegnum = llvmRegnums[reg];
>    mcInst.addOperand(MCOperand::createReg(llvmRegnum));
>  }
>
>
> Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=329673&r1=329672&r2=329673&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
> +++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Mon Apr  9 23:40:51 2018
> @@ -28066,11 +28066,16 @@ X86TargetLowering::EmitInstrWithCustomIn
>          MI.getOpcode() == X86::RDFLAGS32 ? X86::PUSHF32 : X86::PUSHF64;
>      unsigned Pop = MI.getOpcode() == X86::RDFLAGS32 ? X86::POP32r : X86::POP64r;
>      MachineInstr *Push = BuildMI(*BB, MI, DL, TII->get(PushF));
> -    // Permit reads of the FLAGS register without it being defined.
> +    // Permit reads of the EFLAGS and DF registers without them being defined.
>      // This intrinsic exists to read external processor state in flags, such as
>      // the trap flag, interrupt flag, and direction flag, none of which are
>      // modeled by the backend.
> +    assert(Push->getOperand(2).getReg() == X86::EFLAGS &&
> +           "Unexpected register in operand!");
>      Push->getOperand(2).setIsUndef();
> +    assert(Push->getOperand(3).getReg() == X86::DF &&
> +           "Unexpected register in operand!");
> +    Push->getOperand(3).setIsUndef();
>      BuildMI(*BB, MI, DL, TII->get(Pop), MI.getOperand(0).getReg());
>
>      MI.eraseFromParent(); // The pseudo is gone now.
>
> Modified: llvm/trunk/lib/Target/X86/X86InstrCompiler.td
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrCompiler.td?rev=329673&r1=329672&r2=329673&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86InstrCompiler.td (original)
> +++ llvm/trunk/lib/Target/X86/X86InstrCompiler.td Mon Apr  9 23:40:51 2018
> @@ -473,7 +473,7 @@ let Defs = [EAX, ECX, EDX, FP0, FP1, FP2
>              ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
>              MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
>              XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7,
> -            XMM8, XMM9, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, EFLAGS],
> +            XMM8, XMM9, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, EFLAGS, DF],
>      usesCustomInserter = 1, Uses = [ESP, SSP] in {
>  def TLS_addr32 : I<0, Pseudo, (outs), (ins i32mem:$sym),
>                    "# TLS_addr32",
> @@ -493,7 +493,7 @@ let Defs = [RAX, RCX, RDX, RSI, RDI, R8,
>              ST0, ST1, ST2, ST3, ST4, ST5, ST6, ST7,
>              MM0, MM1, MM2, MM3, MM4, MM5, MM6, MM7,
>              XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6, XMM7,
> -            XMM8, XMM9, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, EFLAGS],
> +            XMM8, XMM9, XMM10, XMM11, XMM12, XMM13, XMM14, XMM15, EFLAGS, DF],
>      usesCustomInserter = 1, Uses = [RSP, SSP] in {
>  def TLS_addr64 : I<0, Pseudo, (outs), (ins i64mem:$sym),
>                     "# TLS_addr64",
> @@ -509,7 +509,7 @@ def TLS_base_addr64 : I<0, Pseudo, (outs
>  // For i386, the address of the thunk is passed on the stack, on return the
>  // address of the variable is in %eax.  %ecx is trashed during the function
>  // call.  All other registers are preserved.
> -let Defs = [EAX, ECX, EFLAGS],
> +let Defs = [EAX, ECX, EFLAGS, DF],
>      Uses = [ESP, SSP],
>      usesCustomInserter = 1 in
>  def TLSCall_32 : I<0, Pseudo, (outs), (ins i32mem:$sym),
> @@ -522,7 +522,7 @@ def TLSCall_32 : I<0, Pseudo, (outs), (i
>  // %rdi. The lowering will do the right thing with RDI.
>  // On return the address of the variable is in %rax.  All other
>  // registers are preserved.
> -let Defs = [RAX, EFLAGS],
> +let Defs = [RAX, EFLAGS, DF],
>      Uses = [RSP, SSP],
>      usesCustomInserter = 1 in
>  def TLSCall_64 : I<0, Pseudo, (outs), (ins i64mem:$sym),
>
> Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.cpp?rev=329673&r1=329672&r2=329673&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86InstrInfo.cpp (original)
> +++ llvm/trunk/lib/Target/X86/X86InstrInfo.cpp Mon Apr  9 23:40:51 2018
> @@ -9481,8 +9481,9 @@ bool X86InstrInfo::
>  isSafeToMoveRegClassDefs(const TargetRegisterClass *RC) const {
>    // FIXME: Return false for x87 stack register classes for now. We can't
>    // allow any loads of these registers before FpGet_ST0_80.
> -  return !(RC == &X86::CCRRegClass || RC == &X86::RFP32RegClass ||
> -           RC == &X86::RFP64RegClass || RC == &X86::RFP80RegClass);
> +  return !(RC == &X86::CCRRegClass || RC == &X86::DFCCRRegClass ||
> +           RC == &X86::RFP32RegClass || RC == &X86::RFP64RegClass ||
> +           RC == &X86::RFP80RegClass);
>  }
>
>  /// Return a virtual register initialized with the
>
> Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.td
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.td?rev=329673&r1=329672&r2=329673&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86InstrInfo.td (original)
> +++ llvm/trunk/lib/Target/X86/X86InstrInfo.td Mon Apr  9 23:40:51 2018
> @@ -1235,18 +1235,18 @@ let mayLoad = 1, mayStore = 1, usesCusto
>
>  let mayLoad = 1, mayStore = 1, usesCustomInserter = 1,
>      SchedRW = [WriteRMW] in {
> -  let Defs = [ESP, EFLAGS], Uses = [ESP] in
> +  let Defs = [ESP, EFLAGS, DF], Uses = [ESP] in
>    def WRFLAGS32 : PseudoI<(outs), (ins GR32:$src),
>                     [(int_x86_flags_write_u32 GR32:$src)]>,
>                  Requires<[Not64BitMode]>;
>
> -  let Defs = [RSP, EFLAGS], Uses = [RSP] in
> +  let Defs = [RSP, EFLAGS, DF], Uses = [RSP] in
>    def WRFLAGS64 : PseudoI<(outs), (ins GR64:$src),
>                     [(int_x86_flags_write_u64 GR64:$src)]>,
>                  Requires<[In64BitMode]>;
>  }
>
> -let Defs = [ESP, EFLAGS], Uses = [ESP], mayLoad = 1, hasSideEffects=0,
> +let Defs = [ESP, EFLAGS, DF], Uses = [ESP], mayLoad = 1, hasSideEffects=0,
>      SchedRW = [WriteLoad] in {
>  def POPF16   : I<0x9D, RawFrm, (outs), (ins), "popf{w}", [], IIC_POP_F>,
>                  OpSize16;
> @@ -1254,7 +1254,7 @@ def POPF32   : I<0x9D, RawFrm, (outs), (
>                  OpSize32, Requires<[Not64BitMode]>;
>  }
>
> -let Defs = [ESP], Uses = [ESP, EFLAGS], mayStore = 1, hasSideEffects=0,
> +let Defs = [ESP], Uses = [ESP, EFLAGS, DF], mayStore = 1, hasSideEffects=0,
>      SchedRW = [WriteStore] in {
>  def PUSHF16  : I<0x9C, RawFrm, (outs), (ins), "pushf{w}", [], IIC_PUSH_F>,
>                   OpSize16;
> @@ -1294,10 +1294,10 @@ def PUSH64i32  : Ii32S<0x68, RawFrm, (ou
>                      Requires<[In64BitMode]>;
>  }
>
> -let Defs = [RSP, EFLAGS], Uses = [RSP], mayLoad = 1, hasSideEffects=0 in
> +let Defs = [RSP, EFLAGS, DF], Uses = [RSP], mayLoad = 1, hasSideEffects=0 in
>  def POPF64   : I<0x9D, RawFrm, (outs), (ins), "popfq", [], IIC_POP_FD>,
>                 OpSize32, Requires<[In64BitMode]>, Sched<[WriteLoad]>;
> -let Defs = [RSP], Uses = [RSP, EFLAGS], mayStore = 1, hasSideEffects=0 in
> +let Defs = [RSP], Uses = [RSP, EFLAGS, DF], mayStore = 1, hasSideEffects=0 in
>  def PUSHF64    : I<0x9C, RawFrm, (outs), (ins), "pushfq", [], IIC_PUSH_F>,
>                   OpSize32, Requires<[In64BitMode]>, Sched<[WriteStore]>;
>
> @@ -1382,8 +1382,7 @@ def BSR64rm  : RI<0xBD, MRMSrcMem, (outs
>  } // Defs = [EFLAGS]
>
>  let SchedRW = [WriteMicrocoded] in {
> -// These uses the DF flag in the EFLAGS register to inc or dec EDI and ESI
> -let Defs = [EDI,ESI], Uses = [EDI,ESI,EFLAGS] in {
> +let Defs = [EDI,ESI], Uses = [EDI,ESI,DF] in {
>  def MOVSB : I<0xA4, RawFrmDstSrc, (outs), (ins dstidx8:$dst, srcidx8:$src),
>                "movsb\t{$src, $dst|$dst, $src}", [], IIC_MOVS>;
>  def MOVSW : I<0xA5, RawFrmDstSrc, (outs), (ins dstidx16:$dst, srcidx16:$src),
> @@ -1395,38 +1394,35 @@ def MOVSQ : RI<0xA5, RawFrmDstSrc, (outs
>                 Requires<[In64BitMode]>;
>  }
>
> -// These uses the DF flag in the EFLAGS register to inc or dec EDI and ESI
> -let Defs = [EDI], Uses = [AL,EDI,EFLAGS] in
> +let Defs = [EDI], Uses = [AL,EDI,DF] in
>  def STOSB : I<0xAA, RawFrmDst, (outs), (ins dstidx8:$dst),
>                "stosb\t{%al, $dst|$dst, al}", [], IIC_STOS>;
> -let Defs = [EDI], Uses = [AX,EDI,EFLAGS] in
> +let Defs = [EDI], Uses = [AX,EDI,DF] in
>  def STOSW : I<0xAB, RawFrmDst, (outs), (ins dstidx16:$dst),
>                "stosw\t{%ax, $dst|$dst, ax}", [], IIC_STOS>, OpSize16;
> -let Defs = [EDI], Uses = [EAX,EDI,EFLAGS] in
> +let Defs = [EDI], Uses = [EAX,EDI,DF] in
>  def STOSL : I<0xAB, RawFrmDst, (outs), (ins dstidx32:$dst),
>                "stos{l|d}\t{%eax, $dst|$dst, eax}", [], IIC_STOS>, OpSize32;
> -let Defs = [RDI], Uses = [RAX,RDI,EFLAGS] in
> +let Defs = [RDI], Uses = [RAX,RDI,DF] in
>  def STOSQ : RI<0xAB, RawFrmDst, (outs), (ins dstidx64:$dst),
>                 "stosq\t{%rax, $dst|$dst, rax}", [], IIC_STOS>,
>                 Requires<[In64BitMode]>;
>
> -// These uses the DF flag in the EFLAGS register to inc or dec EDI and ESI
> -let Defs = [EDI,EFLAGS], Uses = [AL,EDI,EFLAGS] in
> +let Defs = [EDI,EFLAGS], Uses = [AL,EDI,DF] in
>  def SCASB : I<0xAE, RawFrmDst, (outs), (ins dstidx8:$dst),
>                "scasb\t{$dst, %al|al, $dst}", [], IIC_SCAS>;
> -let Defs = [EDI,EFLAGS], Uses = [AX,EDI,EFLAGS] in
> +let Defs = [EDI,EFLAGS], Uses = [AX,EDI,DF] in
>  def SCASW : I<0xAF, RawFrmDst, (outs), (ins dstidx16:$dst),
>                "scasw\t{$dst, %ax|ax, $dst}", [], IIC_SCAS>, OpSize16;
> -let Defs = [EDI,EFLAGS], Uses = [EAX,EDI,EFLAGS] in
> +let Defs = [EDI,EFLAGS], Uses = [EAX,EDI,DF] in
>  def SCASL : I<0xAF, RawFrmDst, (outs), (ins dstidx32:$dst),
>                "scas{l|d}\t{$dst, %eax|eax, $dst}", [], IIC_SCAS>, OpSize32;
> -let Defs = [EDI,EFLAGS], Uses = [RAX,EDI,EFLAGS] in
> +let Defs = [EDI,EFLAGS], Uses = [RAX,EDI,DF] in
>  def SCASQ : RI<0xAF, RawFrmDst, (outs), (ins dstidx64:$dst),
>                 "scasq\t{$dst, %rax|rax, $dst}", [], IIC_SCAS>,
>                 Requires<[In64BitMode]>;
>
> -// These uses the DF flag in the EFLAGS register to inc or dec EDI and ESI
> -let Defs = [EDI,ESI,EFLAGS], Uses = [EDI,ESI,EFLAGS] in {
> +let Defs = [EDI,ESI,EFLAGS], Uses = [EDI,ESI,DF] in {
>  def CMPSB : I<0xA6, RawFrmDstSrc, (outs), (ins dstidx8:$dst, srcidx8:$src),
>                "cmpsb\t{$dst, $src|$src, $dst}", [], IIC_CMPS>;
>  def CMPSW : I<0xA7, RawFrmDstSrc, (outs), (ins dstidx16:$dst, srcidx16:$src),
> @@ -2069,8 +2065,7 @@ def DATA32_PREFIX : I<0x66, RawFrm, (out
>  } // SchedRW
>
>  // Repeat string operation instruction prefixes
> -// These use the DF flag in the EFLAGS register to inc or dec ECX
> -let Defs = [ECX], Uses = [ECX,EFLAGS], SchedRW = [WriteMicrocoded] in {
> +let Defs = [ECX], Uses = [ECX,DF], SchedRW = [WriteMicrocoded] in {
>  // Repeat (used with INS, OUTS, MOVS, LODS and STOS)
>  def REP_PREFIX : I<0xF3, RawFrm, (outs),  (ins), "rep", []>;
>  // Repeat while not equal (used with CMPS and SCAS)
> @@ -2079,25 +2074,23 @@ def REPNE_PREFIX : I<0xF2, RawFrm, (outs
>
>  // String manipulation instructions
>  let SchedRW = [WriteMicrocoded] in {
> -// These uses the DF flag in the EFLAGS register to inc or dec EDI and ESI
> -let Defs = [AL,ESI], Uses = [ESI,EFLAGS] in
> +let Defs = [AL,ESI], Uses = [ESI,DF] in
>  def LODSB : I<0xAC, RawFrmSrc, (outs), (ins srcidx8:$src),
>                "lodsb\t{$src, %al|al, $src}", [], IIC_LODS>;
> -let Defs = [AX,ESI], Uses = [ESI,EFLAGS] in
> +let Defs = [AX,ESI], Uses = [ESI,DF] in
>  def LODSW : I<0xAD, RawFrmSrc, (outs), (ins srcidx16:$src),
>                "lodsw\t{$src, %ax|ax, $src}", [], IIC_LODS>, OpSize16;
> -let Defs = [EAX,ESI], Uses = [ESI,EFLAGS] in
> +let Defs = [EAX,ESI], Uses = [ESI,DF] in
>  def LODSL : I<0xAD, RawFrmSrc, (outs), (ins srcidx32:$src),
>                "lods{l|d}\t{$src, %eax|eax, $src}", [], IIC_LODS>, OpSize32;
> -let Defs = [RAX,ESI], Uses = [ESI,EFLAGS] in
> +let Defs = [RAX,ESI], Uses = [ESI,DF] in
>  def LODSQ : RI<0xAD, RawFrmSrc, (outs), (ins srcidx64:$src),
>                 "lodsq\t{$src, %rax|rax, $src}", [], IIC_LODS>,
>                 Requires<[In64BitMode]>;
>  }
>
>  let SchedRW = [WriteSystem] in {
> -// These uses the DF flag in the EFLAGS register to inc or dec EDI and ESI
> -let Defs = [ESI], Uses = [DX,ESI,EFLAGS] in {
> +let Defs = [ESI], Uses = [DX,ESI,DF] in {
>  def OUTSB : I<0x6E, RawFrmSrc, (outs), (ins srcidx8:$src),
>               "outsb\t{$src, %dx|dx, $src}", [], IIC_OUTS>;
>  def OUTSW : I<0x6F, RawFrmSrc, (outs), (ins srcidx16:$src),
> @@ -2106,8 +2099,7 @@ def OUTSL : I<0x6F, RawFrmSrc, (outs), (
>                "outs{l|d}\t{$src, %dx|dx, $src}", [], IIC_OUTS>, OpSize32;
>  }
>
> -// These uses the DF flag in the EFLAGS register to inc or dec EDI and ESI
> -let Defs = [EDI], Uses = [DX,EDI,EFLAGS] in {
> +let Defs = [EDI], Uses = [DX,EDI,DF] in {
>  def INSB : I<0x6C, RawFrmDst, (outs), (ins dstidx8:$dst),
>               "insb\t{%dx, $dst|$dst, dx}", [], IIC_INS>;
>  def INSW : I<0x6D, RawFrmDst, (outs), (ins dstidx16:$dst),
> @@ -2117,19 +2109,22 @@ def INSL : I<0x6D, RawFrmDst, (outs), (i
>  }
>  }
>
> -// Flag instructions
> -let SchedRW = [WriteALU] in {
> +// EFLAGS management instructions.
> +let SchedRW = [WriteALU], Defs = [EFLAGS], Uses = [EFLAGS] in {
>  def CLC : I<0xF8, RawFrm, (outs), (ins), "clc", [], IIC_CLC_CMC_STC>;
>  def STC : I<0xF9, RawFrm, (outs), (ins), "stc", [], IIC_CLC_CMC_STC>;
> -def CLI : I<0xFA, RawFrm, (outs), (ins), "cli", [], IIC_CLI>;
> -def STI : I<0xFB, RawFrm, (outs), (ins), "sti", [], IIC_STI>;
> -def CLD : I<0xFC, RawFrm, (outs), (ins), "cld", [], IIC_CLD>;
> -def STD : I<0xFD, RawFrm, (outs), (ins), "std", [], IIC_STD>;
>  def CMC : I<0xF5, RawFrm, (outs), (ins), "cmc", [], IIC_CLC_CMC_STC>;
> +}
>
> -def CLTS : I<0x06, RawFrm, (outs), (ins), "clts", [], IIC_CLTS>, TB;
> +// DF management instructions.
> +// FIXME: These are a bit more expensive than CLC and STC. We should consider
> +// adjusting their schedule bucket.
> +let SchedRW = [WriteALU], Defs = [DF] in {
> +def CLD : I<0xFC, RawFrm, (outs), (ins), "cld", [], IIC_CLD>;
> +def STD : I<0xFD, RawFrm, (outs), (ins), "std", [], IIC_STD>;
>  }
>
> +
>  // Table lookup instructions
>  let Uses = [AL,EBX], Defs = [AL], hasSideEffects = 0, mayLoad = 1 in
>  def XLAT : I<0xD7, RawFrm, (outs), (ins), "xlatb", [], IIC_XLAT>,
>
> Modified: llvm/trunk/lib/Target/X86/X86InstrSystem.td
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrSystem.td?rev=329673&r1=329672&r2=329673&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86InstrSystem.td (original)
> +++ llvm/trunk/lib/Target/X86/X86InstrSystem.td Mon Apr  9 23:40:51 2018
> @@ -700,6 +700,19 @@ let Uses = [RAX, RBX, RCX, RDX], Defs =
>  } // SchedRW
>
>  //===----------------------------------------------------------------------===//
> +// TS flag control instruction.
> +let SchedRW = [WriteSystem] in {
> +def CLTS : I<0x06, RawFrm, (outs), (ins), "clts", [], IIC_CLTS>, TB;
> +}
> +
> +//===----------------------------------------------------------------------===//
> +// IF (inside EFLAGS) management instructions.
> +let SchedRW = [WriteSystem], Uses = [EFLAGS], Defs = [EFLAGS] in {
> +def CLI : I<0xFA, RawFrm, (outs), (ins), "cli", [], IIC_CLI>;
> +def STI : I<0xFB, RawFrm, (outs), (ins), "sti", [], IIC_STI>;
> +}
> +
> +//===----------------------------------------------------------------------===//
>  // RDPID Instruction
>  let SchedRW = [WriteSystem] in {
>  def RDPID32 : I<0xC7, MRM7r, (outs GR32:$dst), (ins),
>
> Modified: llvm/trunk/lib/Target/X86/X86RegisterInfo.td
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86RegisterInfo.td?rev=329673&r1=329672&r2=329673&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86RegisterInfo.td (original)
> +++ llvm/trunk/lib/Target/X86/X86RegisterInfo.td Mon Apr  9 23:40:51 2018
> @@ -265,9 +265,19 @@ def ST7 : X86Reg<"st(7)", 7>, DwarfRegNu
>  // Floating-point status word
>  def FPSW : X86Reg<"fpsw", 0>;
>
> -// Status flags register
> +// Status flags register.
> +//
> +// Note that some flags that are commonly thought of as part of the status
> +// flags register are modeled separately. Typically this is due to instructions
> +// reading and updating those flags independently of all the others. We don't
> +// want to create false dependencies between these instructions and so we use
> +// a separate register to model them.
>  def EFLAGS : X86Reg<"flags", 0>;
>
> +// The direction flag.
> +def DF : X86Reg<"DF", 0>;
> +
> +
>  // Segment registers
>  def CS : X86Reg<"cs", 1>;
>  def DS : X86Reg<"ds", 3>;
> @@ -510,6 +520,10 @@ def FPCCR : RegisterClass<"X86", [i16],
>    let CopyCost = -1;  // Don't allow copying of status registers.
>    let isAllocatable = 0;
>  }
> +def DFCCR : RegisterClass<"X86", [i32], 32, (add DF)> {
> +  let CopyCost = -1;  // Don't allow copying of status registers.
> +  let isAllocatable = 0;
> +}
>
>  // AVX-512 vector/mask registers.
>  def VR512 : RegisterClass<"X86", [v16f32, v8f64, v64i8, v32i16, v16i32, v8i64],
>
> Modified: llvm/trunk/test/CodeGen/X86/ipra-reg-usage.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/ipra-reg-usage.ll?rev=329673&r1=329672&r2=329673&view=diff
> ==============================================================================
> --- llvm/trunk/test/CodeGen/X86/ipra-reg-usage.ll (original)
> +++ llvm/trunk/test/CodeGen/X86/ipra-reg-usage.ll Mon Apr  9 23:40:51 2018
> @@ -3,7 +3,7 @@
>  target triple = "x86_64-unknown-unknown"
>  declare void @bar1()
>  define preserve_allcc void @foo()#0 {
> -; CHECK: foo Clobbered Registers: $cs $ds $eflags $eip $eiz $es $fpsw $fs $gs $hip $ip $rip $riz $ss $ssp $bnd0 $bnd1 $bnd2 $bnd3 $cr0 $cr1 $cr2 $cr3 $cr4 $cr5 $cr6 $cr7 $cr8 $cr9 $cr10 $cr11 $cr12 $cr13 $cr14 $cr15 $dr0 $dr1 $dr2 $dr3 $dr4 $dr5 $dr6 $dr7 $dr8 $dr9 $dr10 $dr11 $dr12 $dr13 $dr14 $dr15 $fp0 $fp1 $fp2 $fp3 $fp4 $fp5 $fp6 $fp7 $k0 $k1 $k2 $k3 $k4 $k5 $k6 $k7 $mm0 $mm1 $mm2 $mm3 $mm4 $mm5 $mm6 $mm7 $r11 $st0 $st1 $st2 $st3 $st4 $st5 $st6 $st7 $xmm16 $xmm17 $xmm18 $xmm19 $xmm20 $xmm21 $xmm22 $xmm23 $xmm24 $xmm25 $xmm26 $xmm27 $xmm28 $xmm29 $xmm30 $xmm31 $ymm0 $ymm1 $ymm2 $ymm3 $ymm4 $ymm5 $ymm6 $ymm7 $ymm8 $ymm9 $ymm10 $ymm11 $ymm12 $ymm13 $ymm14 $ymm15 $ymm16 $ymm17 $ymm18 $ymm19 $ymm20 $ymm21 $ymm22 $ymm23 $ymm24 $ymm25 $ymm26 $ymm27 $ymm28 $ymm29 $ymm30 $ymm31 $zmm0 $zmm1 $zmm2 $zmm3 $zmm4 $zmm5 $zmm6 $zmm7 $zmm8 $zmm9 $zmm10 $zmm11 $zmm12 $zmm13 $zmm14 $zmm15 $zmm16 $zmm17 $zmm18 $zmm19 $zmm20 $zmm21 $zmm22 $zmm23 $zmm24 $zmm25 $zmm26 $zmm27 $zmm28 $zmm29 $zmm30 $zmm31 $r11b $r11d $r11w
> +; CHECK: foo Clobbered Registers: $cs $df $ds $eflags $eip $eiz $es $fpsw $fs $gs $hip $ip $rip $riz $ss $ssp $bnd0 $bnd1 $bnd2 $bnd3 $cr0 $cr1 $cr2 $cr3 $cr4 $cr5 $cr6 $cr7 $cr8 $cr9 $cr10 $cr11 $cr12 $cr13 $cr14 $cr15 $dr0 $dr1 $dr2 $dr3 $dr4 $dr5 $dr6 $dr7 $dr8 $dr9 $dr10 $dr11 $dr12 $dr13 $dr14 $dr15 $fp0 $fp1 $fp2 $fp3 $fp4 $fp5 $fp6 $fp7 $k0 $k1 $k2 $k3 $k4 $k5 $k6 $k7 $mm0 $mm1 $mm2 $mm3 $mm4 $mm5 $mm6 $mm7 $r11 $st0 $st1 $st2 $st3 $st4 $st5 $st6 $st7 $xmm16 $xmm17 $xmm18 $xmm19 $xmm20 $xmm21 $xmm22 $xmm23 $xmm24 $xmm25 $xmm26 $xmm27 $xmm28 $xmm29 $xmm30 $xmm31 $ymm0 $ymm1 $ymm2 $ymm3 $ymm4 $ymm5 $ymm6 $ymm7 $ymm8 $ymm9 $ymm10 $ymm11 $ymm12 $ymm13 $ymm14 $ymm15 $ymm16 $ymm17 $ymm18 $ymm19 $ymm20 $ymm21 $ymm22 $ymm23 $ymm24 $ymm25 $ymm26 $ymm27 $ymm28 $ymm29 $ymm30 $ymm31 $zmm0 $zmm1 $zmm2 $zmm3 $zmm4 $zmm5 $zmm6 $zmm7 $zmm8 $zmm9 $zmm10 $zmm11 $zmm12 $zmm13 $zmm14 $zmm15 $zmm16 $zmm17 $zmm18 $zmm19 $zmm20 $zmm21 $zmm22 $zmm23 $zmm24 $zmm25 $zmm26 $zmm27 $zmm28 $zmm29 $zmm30 $zmm31 $r11b $r11d $r11w
>    call void @bar1()
>    call void @bar2()
>    ret void
>
>
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