[llvm] r306388 - [globalisel][tablegen] Add support for EXTRACT_SUBREG.

Daniel Sanders via llvm-commits llvm-commits at lists.llvm.org
Tue Jun 27 09:07:49 PDT 2017


Hi David,

Sure, the main thing is that we inspect larger classes first. The order of equal-sized classes shouldn't matter too much.

> On 27 Jun 2017, at 16:48, David Green <David.Green at arm.com> wrote:
> 
> Hello,
> 
> We appear to have a windows-debug build error from what I think is this commit, a crash in tblgen:
> 
>                  0x00007FF9E6CA0806 (0x00007FF735189138 0x00007FF735188DE0 0x000000F300000A52 0xCCCCCCCCCCCCCCCC), ?_Debug_message at std@@YAXPEB_W0I at Z() + 0x46 bytes(s)
>                  0x00007FF7345F58E1 (0x000000F3A0A6CA50 0x000000F3A0A6C898 0x000000F3A5BB8570 0x00007FF735188DE0), std::_Debug_lt_pred<<lambda_83a80e87367d92ad251c7c618cd76f21> & __ptr64,std::pair<llvm::CodeGenRegisterClass * __ptr64,llvm::BitVector> & __ptr64,std::pair<llvm::CodeGenRegisterClass * __ptr64,llvm::BitVector> & __ptr64>() + 0x81 bytes(s), c:\program files (x86)\microsoft visual studio 14.0\vc\include\xutility, line 896 + 0x54 byte(s)
>                  0x00007FF734608251 (0x000000F3A5BB8550 0x000000F3A5BB85F0 0x000000F3A0A6CA50 0xCCCCCCCCCCCCCCCC), std::_Insertion_sort_unchecked<std::pair<llvm::CodeGenRegisterClass * __ptr64,llvm::BitVector> * __ptr64,<lambda_83a80e87367d92ad251c7c618cd76f21> >() + 0x151 bytes(s), c:\program files (x86)\microsoft visual studio 14.0\vc\include\algorithm, line 2642 + 0x34 byte(s)
>                  0x00007FF734611B78 (0x000000F3A5BB8550 0x000000F3A5BB85F0 0x0000000000000005 0x000000F3A0A6CA50), std::_Sort_unchecked1<std::pair<llvm::CodeGenRegisterClass * __ptr64,llvm::BitVector> * __ptr64,__int64,<lambda_83a80e87367d92ad251c7c618cd76f21> >() + 0x198 bytes(s), c:\program files (x86)\microsoft visual studio 14.0\vc\include\algorithm, line 2770
>                  0x00007FF734611E13 (0x000000F3A5BB8550 0x000000F3A5BB85F0 0x000000F3A0A6CA50 0xCCCCCCCC00000ADF), std::_Sort_unchecked<std::pair<llvm::CodeGenRegisterClass * __ptr64,llvm::BitVector> * __ptr64,<lambda_83a80e87367d92ad251c7c618cd76f21> >() + 0x53 bytes(s), c:\program files (x86)\microsoft visual studio 14.0\vc\include\algorithm, line 2777
>                  0x00007FF7346232E2 (0x000000F3A0A6CDF8 0x000000F3A0A6CDD8 0x000000F3A0A6CA64 0xCCCCCCCCCCCCCCCC), std::sort<std::_Vector_iterator<std::_Vector_val<std::_Simple_types<std::pair<llvm::CodeGenRegisterClass * __ptr64,llvm::BitVector> > > >,<lambda_83a80e87367d92ad251c7c618cd76f21> >() + 0x102 bytes(s), c:\program files (x86)\microsoft visual studio 14.0\vc\include\algorithm, line 2785
>                  0x00007FF7345DA928 (0x000000F3A8B9AAF0 0x000000F3A0A6CF58 0x000000F3A0A6E868 0x000000F3A5BB4150), llvm::CodeGenRegisterClass::getMatchingSubClassWithSubRegs() + 0x428 bytes(s), c:\work\trunk\work\src\llvm\utils\tablegen\codegenregisters.cpp, line 964
>                  0x00007FF7348051B8 (0x000000F3A0A6E660 0x000000F3A0A6D848 0x000000F3A0A6D470 0x000000F3A989E3F0), `anonymous namespace'::GlobalISelEmitter::createAndImportInstructionRenderer() + 0x5F8 bytes(s), c:\work\trunk\work\src\llvm\utils\tablegen\globaliselemitter.cpp, line 1674 + 0x2E byte(s)
>                  0x00007FF7348071CA (0x000000F3A0A6E660 0x000000F3A0A6DF40 0x000000F3A9BD09A0 0xCCCCCCCCCCCCCCCC), `anonymous namespace'::GlobalISelEmitter::runOnPattern() + 0xDEA bytes(s), c:\work\trunk\work\src\llvm\utils\tablegen\globaliselemitter.cpp, line 1840
>                  0x00007FF734802866 (0x000000F3A0A6E660 0x000000F3A0A6F290 0xCCCCCCCCCCCCCCCC 0xCCCCCCCCCCCCCCCC), `anonymous namespace'::GlobalISelEmitter::run() + 0x1D6 bytes(s), c:\work\trunk\work\src\llvm\utils\tablegen\globaliselemitter.cpp, line 1934
>                  0x00007FF734807B2D (0x000000F3A0A6EFA8 0x000000F3A0A6F290 0xCCCCCCCCCCCCCCCC 0xCCCCCCCCCCCCCCCC), llvm::EmitGlobalISel() + 0x5D bytes(s), c:\work\trunk\work\src\llvm\utils\tablegen\globaliselemitter.cpp, line 2056 + 0x22 byte(s)
>                  0x00007FF73497AA39 (0x000000F3A0A6F290 0x000000F3A0A6EFA8 0x000000F3A0A6F228 0xCCCCCCCC00000004), `anonymous namespace'::LLVMTableGenMain() + 0x739 bytes(s), c:\work\trunk\work\src\llvm\utils\tablegen\tablegen.cpp, line 192
>                  0x00007FF734B2A155 (0x000000F3A0C9F210 0x00007FF73497A300 0x000000F3A0A6F670 0x0000000000000000), llvm::TableGenMain() + 0x605 bytes(s), c:\work\trunk\work\src\llvm\lib\tablegen\main.cpp, line 109 + 0x1C byte(s)
>                  0x00007FF73497ABFD (0x00007FF70000000B 0x000000F3A0C9F1B0 0x0000000000000000 0x00007FF73516ABD0), main() + 0x10D bytes(s), c:\work\trunk\work\src\llvm\utils\tablegen\tablegen.cpp, line 212 + 0x21 byte(s)
>                  0x00007FF734FC4584 (0x00007FF73516A000 0x00007FF73516A670 0x0000000000000000 0x0000000000000000), invoke_main() + 0x34 bytes(s), f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl, line 65
>                  0x00007FF734FC4447 (0x0000000000000000 0x0000000000000000 0x0000000000000000 0x0000000000000000), __scrt_common_main_seh() + 0x127 bytes(s), f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl, line 253 + 0x5 byte(s)
>                  0x00007FF734FC430E (0x0000000000000000 0x0000000000000000 0x0000000000000000 0x0000000000000000), __scrt_common_main() + 0xE bytes(s), f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl, line 296
>                  0x00007FF734FC45A9 (0x0000000000000000 0x0000000000000000 0x0000000000000000 0x0000000000000000), mainCRTStartup() + 0x9 bytes(s), f:\dd\vctools\crt\vcstartup\src\startup\exe_main.cpp, line 17
>                  0x00007FF9FC9D13D2 (0x00007FF9FC9D13B0 0x0000000000000000 0x0000000000000000 0x0000000000000000), BaseThreadInitThunk() + 0x22 bytes(s)
>                  0x00007FF9FCB254E4 (0x0000000000000000 0x0000000000000000 0x0000000000000000 0x0000000000000000), RtlUserThreadStart() + 0x34 bytes(s)
> 
> Sorry if that is hard to read. It looks like it's complaining about the SizeOrder lambda not being in strict weak ordering. Changing the "return A->getMembers().size() >= B->getMembers().size();" to be a ">" seems to get it build.
> 
> Are you happy to make that a ">"?
> 
> Cheers
> Dave
> 
> From: llvm-commits <llvm-commits-bounces at lists.llvm.org> on behalf of Daniel Sanders via llvm-commits <llvm-commits at lists.llvm.org>
> Sent: 27 June 2017 11:11
> To: llvm-commits at lists.llvm.org
> Subject: [llvm] r306388 - [globalisel][tablegen] Add support for EXTRACT_SUBREG.
>  
> Author: dsanders
> Date: Tue Jun 27 03:11:39 2017
> New Revision: 306388
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=306388&view=rev <http://llvm.org/viewvc/llvm-project?rev=306388&view=rev>
> Log:
> [globalisel][tablegen] Add support for EXTRACT_SUBREG.
> 
> Summary:
> After this patch, we finally have test cases that require multiple
> instruction emission.
> 
> Depends on D33590
> 
> Reviewers: ab, qcolombet, t.p.northover, rovka, kristof.beyls
> 
> Subscribers: javed.absar, llvm-commits, igorb
> 
> Differential Revision: https://reviews.llvm.org/D33596 <https://reviews.llvm.org/D33596>
> 
> Modified:
>     llvm/trunk/lib/Target/AArch64/AArch64InstructionSelector.cpp
>     llvm/trunk/test/CodeGen/AArch64/GlobalISel/select-trunc.mir
>     llvm/trunk/utils/TableGen/CodeGenRegisters.cpp
>     llvm/trunk/utils/TableGen/CodeGenRegisters.h
>     llvm/trunk/utils/TableGen/GlobalISelEmitter.cpp
> 
> Modified: llvm/trunk/lib/Target/AArch64/AArch64InstructionSelector.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AArch64/AArch64InstructionSelector.cpp?rev=306388&r1=306387&r2=306388&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/AArch64/AArch64InstructionSelector.cpp?rev=306388&r1=306387&r2=306388&view=diff>
> ==============================================================================
> --- llvm/trunk/lib/Target/AArch64/AArch64InstructionSelector.cpp (original)
> +++ llvm/trunk/lib/Target/AArch64/AArch64InstructionSelector.cpp Tue Jun 27 03:11:39 2017
> @@ -947,7 +947,7 @@ bool AArch64InstructionSelector::select(
>      const RegisterBank &SrcRB = *RBI.getRegBank(SrcReg, MRI, TRI);
>  
>      if (DstRB.getID() != SrcRB.getID()) {
> -      DEBUG(dbgs() << "G_TRUNC input/output on different banks\n");
> +      DEBUG(dbgs() << "G_TRUNC/G_PTRTOINT input/output on different banks\n");
>        return false;
>      }
>  
> @@ -964,16 +964,21 @@ bool AArch64InstructionSelector::select(
>  
>        if (!RBI.constrainGenericRegister(SrcReg, *SrcRC, MRI) ||
>            !RBI.constrainGenericRegister(DstReg, *DstRC, MRI)) {
> -        DEBUG(dbgs() << "Failed to constrain G_TRUNC\n");
> +        DEBUG(dbgs() << "Failed to constrain G_TRUNC/G_PTRTOINT\n");
>          return false;
>        }
>  
>        if (DstRC == SrcRC) {
>          // Nothing to be done
> +      } else if (Opcode == TargetOpcode::G_TRUNC && DstTy == LLT::scalar(32) &&
> +                 SrcTy == LLT::scalar(64)) {
> +        llvm_unreachable("TableGen can import this case");
> +        return false;
>        } else if (DstRC == &AArch64::GPR32RegClass &&
>                   SrcRC == &AArch64::GPR64RegClass) {
>          I.getOperand(1).setSubReg(AArch64::sub_32);
>        } else {
> +        DEBUG(dbgs() << "Unhandled mismatched classes in G_TRUNC/G_PTRTOINT\n");
>          return false;
>        }
>  
> 
> Modified: llvm/trunk/test/CodeGen/AArch64/GlobalISel/select-trunc.mir
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/GlobalISel/select-trunc.mir?rev=306388&r1=306387&r2=306388&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/GlobalISel/select-trunc.mir?rev=306388&r1=306387&r2=306388&view=diff>
> ==============================================================================
> --- llvm/trunk/test/CodeGen/AArch64/GlobalISel/select-trunc.mir (original)
> +++ llvm/trunk/test/CodeGen/AArch64/GlobalISel/select-trunc.mir Tue Jun 27 03:11:39 2017
> @@ -15,8 +15,8 @@ legalized:       true
>  regBankSelected: true
>  
>  # CHECK:      registers:
> -# CHECK-NEXT:  - { id: 0, class: gpr64, preferred-register: '' }
> -# CHECK-NEXT:  - { id: 1, class: gpr32, preferred-register: '' }
> +# CHECK-NEXT:  - { id: 0, class: gpr64sp, preferred-register: '' }
> +# CHECK-NEXT:  - { id: 1, class: gpr32sp, preferred-register: '' }
>  registers:
>    - { id: 0, class: gpr }
>    - { id: 1, class: gpr }
> 
> Modified: llvm/trunk/utils/TableGen/CodeGenRegisters.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/CodeGenRegisters.cpp?rev=306388&r1=306387&r2=306388&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/CodeGenRegisters.cpp?rev=306388&r1=306387&r2=306388&view=diff>
> ==============================================================================
> --- llvm/trunk/utils/TableGen/CodeGenRegisters.cpp (original)
> +++ llvm/trunk/utils/TableGen/CodeGenRegisters.cpp Tue Jun 27 03:11:39 2017
> @@ -915,6 +915,84 @@ void CodeGenRegisterClass::computeSubCla
>        RC.inheritProperties(RegBank);
>  }
>  
> +Optional<std::pair<CodeGenRegisterClass *, CodeGenRegisterClass *>>
> +CodeGenRegisterClass::getMatchingSubClassWithSubRegs(
> +    CodeGenRegBank &RegBank, const CodeGenSubRegIndex *SubIdx) const {
> +  auto SizeOrder = [](const CodeGenRegisterClass *A,
> +                      const CodeGenRegisterClass *B) {
> +    return A->getMembers().size() >= B->getMembers().size();
> +  };
> +
> +  auto &RegClasses = RegBank.getRegClasses();
> +
> +  // Find all the subclasses of this one that fully support the sub-register
> +  // index and order them by size. BiggestSuperRC should always be first.
> +  CodeGenRegisterClass *BiggestSuperRegRC = getSubClassWithSubReg(SubIdx);
> +  if (!BiggestSuperRegRC)
> +    return None;
> +  BitVector SuperRegRCsBV = BiggestSuperRegRC->getSubClasses();
> +  std::vector<CodeGenRegisterClass *> SuperRegRCs;
> +  for (auto &RC : RegClasses)
> +    if (SuperRegRCsBV[RC.EnumValue])
> +      SuperRegRCs.emplace_back(&RC);
> +  std::sort(SuperRegRCs.begin(), SuperRegRCs.end(), SizeOrder);
> +  assert(SuperRegRCs.front() == BiggestSuperRegRC && "Biggest class wasn't first");
> +
> +  // Find all the subreg classes and order them by size too.
> +  std::vector<std::pair<CodeGenRegisterClass *, BitVector>> SuperRegClasses;
> +  for (auto &RC: RegClasses) {
> +    BitVector SuperRegClassesBV(RegClasses.size());
> +    RC.getSuperRegClasses(SubIdx, SuperRegClassesBV);
> +    if (SuperRegClassesBV.any())
> +      SuperRegClasses.push_back(std::make_pair(&RC, SuperRegClassesBV));
> +  }
> +  std::sort(SuperRegClasses.begin(), SuperRegClasses.end(),
> +            [&](const std::pair<CodeGenRegisterClass *, BitVector> &A,
> +                const std::pair<CodeGenRegisterClass *, BitVector> &B) {
> +              return SizeOrder(A.first, B.first);
> +            });
> +
> +  // Find the biggest subclass and subreg class such that R:subidx is in the
> +  // subreg class for all R in subclass.
> +  //
> +  // For example:
> +  // All registers in X86's GR64 have a sub_32bit subregister but no class
> +  // exists that contains all the 32-bit subregisters because GR64 contains RIP
> +  // but GR32 does not contain EIP. Instead, we constrain SuperRegRC to
> +  // GR32_with_sub_8bit (which is identical to GR32_with_sub_32bit) and then,
> +  // having excluded RIP, we are able to find a SubRegRC (GR32).
> +  CodeGenRegisterClass *ChosenSuperRegClass = nullptr;
> +  CodeGenRegisterClass *SubRegRC = nullptr;
> +  for (auto *SuperRegRC : SuperRegRCs) {
> +    for (const auto &SuperRegClassPair : SuperRegClasses) {
> +      const BitVector &SuperRegClassBV = SuperRegClassPair.second;
> +      if (SuperRegClassBV[SuperRegRC->EnumValue]) {
> +        SubRegRC = SuperRegClassPair.first;
> +        ChosenSuperRegClass = SuperRegRC;
> +
> +        // If SubRegRC is bigger than SuperRegRC then there are members of
> +        // SubRegRC that don't have super registers via SubIdx. Keep looking to
> +        // find a better fit and fall back on this one if there isn't one.
> +        //
> +        // This is intended to prevent X86 from making odd choices such as
> +        // picking LOW32_ADDR_ACCESS_RBP instead of GR32 in the example above.
> +        // LOW32_ADDR_ACCESS_RBP is a valid choice but contains registers that
> +        // aren't subregisters of SuperRegRC whereas GR32 has a direct 1:1
> +        // mapping.
> +        if (SuperRegRC->getMembers().size() >= SubRegRC->getMembers().size())
> +          return std::make_pair(ChosenSuperRegClass, SubRegRC);
> +      }
> +    }
> +
> +    // If we found a fit but it wasn't quite ideal because SubRegRC had excess
> +    // registers, then we're done.
> +    if (ChosenSuperRegClass)
> +      return std::make_pair(ChosenSuperRegClass, SubRegRC);
> +  }
> +
> +  return None;
> +}
> +
>  void CodeGenRegisterClass::getSuperRegClasses(const CodeGenSubRegIndex *SubIdx,
>                                                BitVector &Out) const {
>    auto FindI = SuperRegClasses.find(SubIdx);
> 
> Modified: llvm/trunk/utils/TableGen/CodeGenRegisters.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/CodeGenRegisters.h?rev=306388&r1=306387&r2=306388&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/CodeGenRegisters.h?rev=306388&r1=306387&r2=306388&view=diff>
> ==============================================================================
> --- llvm/trunk/utils/TableGen/CodeGenRegisters.h (original)
> +++ llvm/trunk/utils/TableGen/CodeGenRegisters.h Tue Jun 27 03:11:39 2017
> @@ -329,6 +329,9 @@ namespace llvm {
>      const std::string &getName() const { return Name; }
>      std::string getQualifiedName() const;
>      ArrayRef<MVT::SimpleValueType> getValueTypes() const {return VTs;}
> +    bool hasValueType(MVT::SimpleValueType VT) const {
> +      return std::find(VTs.begin(), VTs.end(), VT) != VTs.end();
> +    }
>      unsigned getNumValueTypes() const { return VTs.size(); }
>  
>      MVT::SimpleValueType getValueTypeNum(unsigned VTNum) const {
> @@ -360,6 +363,18 @@ namespace llvm {
>        return SubClassWithSubReg.lookup(SubIdx);
>      }
>  
> +    /// Find largest subclass where all registers have SubIdx subregisters in
> +    /// SubRegClass and the largest subregister class that contains those
> +    /// subregisters without (as far as possible) also containing additional registers.
> +    ///
> +    /// This can be used to find a suitable pair of classes for subregister copies.
> +    /// \return std::pair<SubClass, SubRegClass> where SubClass is a SubClass is
> +    /// a class where every register has SubIdx and SubRegClass is a class where
> +    /// every register is covered by the SubIdx subregister of SubClass.
> +    Optional<std::pair<CodeGenRegisterClass *, CodeGenRegisterClass *>>
> +    getMatchingSubClassWithSubRegs(CodeGenRegBank &RegBank,
> +                                   const CodeGenSubRegIndex *SubIdx) const;
> +
>      void setSubClassWithSubReg(const CodeGenSubRegIndex *SubIdx,
>                                 CodeGenRegisterClass *SubRC) {
>        SubClassWithSubReg[SubIdx] = SubRC;
> @@ -370,7 +385,7 @@ namespace llvm {
>      void getSuperRegClasses(const CodeGenSubRegIndex *SubIdx,
>                              BitVector &Out) const;
>  
> -    // addSuperRegClass - Add a class containing only SudIdx super-registers.
> +    // addSuperRegClass - Add a class containing only SubIdx super-registers.
>      void addSuperRegClass(CodeGenSubRegIndex *SubIdx,
>                            CodeGenRegisterClass *SuperRC) {
>        SuperRegClasses[SubIdx].insert(SuperRC);
> 
> Modified: llvm/trunk/utils/TableGen/GlobalISelEmitter.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/GlobalISelEmitter.cpp?rev=306388&r1=306387&r2=306388&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/GlobalISelEmitter.cpp?rev=306388&r1=306387&r2=306388&view=diff>
> ==============================================================================
> --- llvm/trunk/utils/TableGen/GlobalISelEmitter.cpp (original)
> +++ llvm/trunk/utils/TableGen/GlobalISelEmitter.cpp Tue Jun 27 03:11:39 2017
> @@ -832,7 +832,13 @@ public:
>  //===- Actions ------------------------------------------------------------===//
>  class OperandRenderer {
>  public:
> -  enum RendererKind { OR_Copy, OR_Imm, OR_Register, OR_ComplexPattern };
> +  enum RendererKind {
> +    OR_Copy,
> +    OR_CopySubReg,
> +    OR_Imm,
> +    OR_Register,
> +    OR_ComplexPattern
> +  };
>  
>  protected:
>    RendererKind Kind;
> @@ -877,6 +883,42 @@ public:
>    }
>  };
>  
> +/// A CopySubRegRenderer emits code to copy a single register operand from an
> +/// existing instruction to the one being built and indicate that only a
> +/// subregister should be copied.
> +class CopySubRegRenderer : public OperandRenderer {
> +protected:
> +  /// The matcher for the instruction that this operand is copied from.
> +  /// This provides the facility for looking up an a operand by it's name so
> +  /// that it can be used as a source for the instruction being built.
> +  const InstructionMatcher &Matched;
> +  /// The name of the operand.
> +  const StringRef SymbolicName;
> +  /// The subregister to extract.
> +  const CodeGenSubRegIndex *SubReg;
> +
> +public:
> +  CopySubRegRenderer(const InstructionMatcher &Matched, StringRef SymbolicName,
> +                     const CodeGenSubRegIndex *SubReg)
> +      : OperandRenderer(OR_CopySubReg), Matched(Matched),
> +        SymbolicName(SymbolicName), SubReg(SubReg) {}
> +
> +  static bool classof(const OperandRenderer *R) {
> +    return R->getKind() == OR_CopySubReg;
> +  }
> +
> +  const StringRef getSymbolicName() const { return SymbolicName; }
> +
> +  void emitCxxRenderStmts(raw_ostream &OS, RuleMatcher &Rule) const override {
> +    const OperandMatcher &Operand = Matched.getOperand(SymbolicName);
> +    StringRef InsnVarName =
> +        Rule.getInsnVarName(Operand.getInstructionMatcher());
> +    std::string OperandExpr = Operand.getOperandExpr(InsnVarName);
> +    OS << "    MIB.addReg(" << OperandExpr << ".getReg() /*" << SymbolicName
> +       << "*/, 0, " << SubReg->EnumValue << ");\n";
> +  }
> +};
> +
>  /// Adds a specific physical register to the instruction being built.
>  /// This is typically useful for WZR/XZR on AArch64.
>  class AddRegisterRenderer : public OperandRenderer {
> @@ -1292,6 +1334,7 @@ private:
>    const RecordKeeper &RK;
>    const CodeGenDAGPatterns CGP;
>    const CodeGenTarget &Target;
> +  CodeGenRegBank CGRegs;
>  
>    /// Keep track of the equivalence between SDNodes and Instruction.
>    /// This is defined using 'GINodeEquiv' in the target description.
> @@ -1315,9 +1358,9 @@ private:
>    Error importChildMatcher(InstructionMatcher &InsnMatcher,
>                             const TreePatternNode *SrcChild, unsigned OpIdx,
>                             unsigned &TempOpIdx) const;
> -  Expected<BuildMIAction &> createAndImportInstructionRenderer(
> -      RuleMatcher &M, const TreePatternNode *Dst,
> -      const InstructionMatcher &InsnMatcher) const;
> +  Expected<BuildMIAction &>
> +  createAndImportInstructionRenderer(RuleMatcher &M, const TreePatternNode *Dst,
> +                                     const InstructionMatcher &InsnMatcher);
>    Error importExplicitUseRenderer(BuildMIAction &DstMIBuilder,
>                                    TreePatternNode *DstChild,
>                                    const InstructionMatcher &InsnMatcher) const;
> @@ -1354,7 +1397,7 @@ const CodeGenInstruction *GlobalISelEmit
>  }
>  
>  GlobalISelEmitter::GlobalISelEmitter(RecordKeeper &RK)
> -    : RK(RK), CGP(RK), Target(CGP.getTargetInfo()) {}
> +    : RK(RK), CGP(RK), Target(CGP.getTargetInfo()), CGRegs(RK) {}
>  
>  //===- Emitter ------------------------------------------------------------===//
>  
> @@ -1585,7 +1628,7 @@ Error GlobalISelEmitter::importExplicitU
>  
>  Expected<BuildMIAction &> GlobalISelEmitter::createAndImportInstructionRenderer(
>      RuleMatcher &M, const TreePatternNode *Dst,
> -    const InstructionMatcher &InsnMatcher) const {
> +    const InstructionMatcher &InsnMatcher) {
>    Record *DstOp = Dst->getOperator();
>    if (!DstOp->isSubClassOf("Instruction")) {
>      if (DstOp->isSubClassOf("ValueType"))
> @@ -1597,13 +1640,17 @@ Expected<BuildMIAction &> GlobalISelEmit
>  
>    unsigned DstINumUses = DstI->Operands.size() - DstI->Operands.NumDefs;
>    unsigned ExpectedDstINumUses = Dst->getNumChildren();
> +  bool IsExtractSubReg = false;
>  
>    // COPY_TO_REGCLASS is just a copy with a ConstrainOperandToRegClassAction
> -  // attached.
> +  // attached. Similarly for EXTRACT_SUBREG except that's a subregister copy.
>    if (DstI->TheDef->getName() == "COPY_TO_REGCLASS") {
>      DstI = &Target.getInstruction(RK.getDef("COPY"));
>      DstINumUses--; // Ignore the class constraint.
>      ExpectedDstINumUses--;
> +  } else if (DstI->TheDef->getName() == "EXTRACT_SUBREG") {
> +    DstI = &Target.getInstruction(RK.getDef("COPY"));
> +    IsExtractSubReg = true;
>    }
>  
>    auto &DstMIBuilder = M.addAction<BuildMIAction>("NewI", DstI, InsnMatcher);
> @@ -1614,6 +1661,32 @@ Expected<BuildMIAction &> GlobalISelEmit
>      DstMIBuilder.addRenderer<CopyRenderer>(InsnMatcher, DstIOperand.Name);
>    }
>  
> +  // EXTRACT_SUBREG needs to use a subregister COPY.
> +  if (IsExtractSubReg) {
> +    if (!Dst->getChild(0)->isLeaf())
> +      return failedImport("EXTRACT_SUBREG child #1 is not a leaf");
> +
> +    if (DefInit *SubRegInit = dyn_cast<DefInit>(Dst->getChild(1)->getLeafValue())) {
> +      CodeGenRegisterClass *RC = CGRegs.getRegClass(
> +          getInitValueAsRegClass(Dst->getChild(0)->getLeafValue()));
> +      CodeGenSubRegIndex *SubIdx = CGRegs.getSubRegIdx(SubRegInit->getDef());
> +
> +      const auto &SrcRCDstRCPair =
> +          RC->getMatchingSubClassWithSubRegs(CGRegs, SubIdx);
> +      if (SrcRCDstRCPair.hasValue()) {
> +        assert(SrcRCDstRCPair->second && "Couldn't find a matching subclass");
> +        if (SrcRCDstRCPair->first != RC)
> +          return failedImport("EXTRACT_SUBREG requires an additional COPY");
> +      }
> +
> +      DstMIBuilder.addRenderer<CopySubRegRenderer>(
> +          InsnMatcher, Dst->getChild(0)->getName(), SubIdx);
> +      return DstMIBuilder;
> +    }
> +
> +    return failedImport("EXTRACT_SUBREG child #1 is not a subreg index");
> +  }
> +
>    // Render the explicit uses.
>    unsigned Child = 0;
>    unsigned NumDefaultOps = 0;
> @@ -1740,6 +1813,16 @@ Expected<RuleMatcher> GlobalISelEmitter:
>        if (DstIOpRec == nullptr)
>          return failedImport(
>              "COPY_TO_REGCLASS operand #1 isn't a register class");
> +    } else if (DstI.TheDef->getName() == "EXTRACT_SUBREG") {
> +      if (!Dst->getChild(0)->isLeaf())
> +        return failedImport("EXTRACT_SUBREG operand #0 isn't a leaf");
> +
> +      // We can assume that a subregister is in the same bank as it's super register.
> +      DstIOpRec = getInitValueAsRegClass(Dst->getChild(0)->getLeafValue());
> +
> +      if (DstIOpRec == nullptr)
> +        return failedImport(
> +            "EXTRACT_SUBREG operand #0 isn't a register class");
>      } else if (DstIOpRec->isSubClassOf("RegisterOperand"))
>        DstIOpRec = DstIOpRec->getValueAsDef("RegClass");
>      else if (!DstIOpRec->isSubClassOf("RegisterClass"))
> @@ -1776,8 +1859,58 @@ Expected<RuleMatcher> GlobalISelEmitter:
>  
>      M.addAction<ConstrainOperandToRegClassAction>(
>          "NewI", 0, Target.getRegisterClass(DstIOpRec));
> -  } else
> -    M.addAction<ConstrainOperandsToDefinitionAction>("NewI");
> +
> +    // We're done with this pattern!  It's eligible for GISel emission; return
> +    // it.
> +    ++NumPatternImported;
> +    return std::move(M);
> +  }
> +
> +  if (DstI.TheDef->getName() == "EXTRACT_SUBREG") {
> +    // EXTRACT_SUBREG selects into a subregister COPY but unlike most
> +    // instructions, the result register class is controlled by the
> +    // subregisters of the operand. As a result, we must constrain the result
> +    // class rather than check that it's already the right one.
> +    if (!Dst->getChild(0)->isLeaf())
> +      return failedImport("EXTRACT_SUBREG child #1 is not a leaf");
> +
> +    if (DefInit *SubRegInit =
> +            dyn_cast<DefInit>(Dst->getChild(1)->getLeafValue())) {
> +      // Constrain the result to the same register bank as the operand.
> +      Record *DstIOpRec =
> +          getInitValueAsRegClass(Dst->getChild(0)->getLeafValue());
> +
> +      if (DstIOpRec == nullptr)
> +        return failedImport("EXTRACT_SUBREG operand #1 isn't a register class");
> +
> +      CodeGenSubRegIndex *SubIdx = CGRegs.getSubRegIdx(SubRegInit->getDef());
> +      CodeGenRegisterClass *SrcRC = CGRegs.getRegClass(
> +          getInitValueAsRegClass(Dst->getChild(0)->getLeafValue()));
> +
> +      // It would be nice to leave this constraint implicit but we're required
> +      // to pick a register class so constrain the result to a register class
> +      // that can hold the correct MVT.
> +      //
> +      // FIXME: This may introduce an extra copy if the chosen class doesn't
> +      //        actually contain the subregisters.
> +      assert(Src->getExtTypes().size() == 1);
> +
> +      const auto &SrcRCDstRCPair =
> +          SrcRC->getMatchingSubClassWithSubRegs(CGRegs, SubIdx);
> +      assert(SrcRCDstRCPair->second && "Couldn't find a matching subclass");
> +      M.addAction<ConstrainOperandToRegClassAction>("NewI", 0, *SrcRCDstRCPair->second);
> +      M.addAction<ConstrainOperandToRegClassAction>("NewI", 1, *SrcRCDstRCPair->first);
> +
> +      // We're done with this pattern!  It's eligible for GISel emission; return
> +      // it.
> +      ++NumPatternImported;
> +      return std::move(M);
> +    }
> +
> +    return failedImport("EXTRACT_SUBREG child #1 is not a subreg index");
> +  }
> +
> +  M.addAction<ConstrainOperandsToDefinitionAction>("NewI");
>  
>    // We're done with this pattern!  It's eligible for GISel emission; return it.
>    ++NumPatternImported;
> 
> 
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