[RegisterBankInfo] Add methods to get the possible mapping of an instruction on a register bank.

This will be used by the register bank select pass to assign register banks
for generic virtual registers.

llvm-svn: 265573

include/llvm/CodeGen/GlobalISel/RegisterBankInfo.h

@@ -16,6 +16,7 @@
 #define LLVM_CODEGEN_GLOBALISEL_REGBANKINFO_H
 
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/CodeGen/GlobalISel/RegisterBank.h"
 #include "llvm/CodeGen/GlobalISel/Types.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -123,6 +124,11 @@ public:
     void verify(const MachineInstr &MI) const;
   };
 
+  /// Convenient type to represent the alternatives for mapping an
+  /// instruction.
+  /// \todo When we move to TableGen this should be an array ref.
+  typedef SmallVector<InstructionMapping, 4> InstructionMappings;
+
 protected:
   /// Hold the set of supported register banks.
   std::unique_ptr<RegisterBank[]> RegBanks;
@@ -196,6 +202,69 @@ public:
     return 0;
   }
 
+  /// Identifier used when the related instruction mapping instance
+  /// is generated by target independent code.
+  /// Make sure not to use that identifier to avoid possible collision.
+  static const unsigned DefaultMappingID;
+
+  /// Get the mapping of the different operands of \p MI
+  /// on the register bank.
+  /// This mapping should be the direct translation of \p MI.
+  /// The target independent implementation gives a mapping based on
+  /// the register classes for the target specific opcode.
+  /// It uses the ID RegisterBankInfo::DefaultMappingID for that mapping.
+  /// Make sure you do not use that ID for the alternative mapping
+  /// for MI. See getInstrAlternativeMappings for the alternative
+  /// mappings.
+  ///
+  /// For instance, if \p MI is a vector add, the mapping should
+  /// not be a scalarization of the add.
+  ///
+  /// \post returnedVal.verify(MI).
+  ///
+  /// \note If returnedVal does not verify MI, this would probably mean
+  /// that the target does not support that instruction.
+  virtual InstructionMapping getInstrMapping(const MachineInstr &MI) const;
+
+  /// Get the alternative mappings for \p MI.
+  /// Alternative in the sense different from getInstrMapping.
+  virtual InstructionMappings
+  getInstrAlternativeMappings(const MachineInstr &MI) const {
+    // No alternative for MI.
+    return InstructionMappings();
+  }
+
+  /// Get the possible mapping for \p MI.
+  /// A mapping defines where the different operands may live and at what cost.
+  /// For instance, let us consider:
+  /// v0(16) = G_ADD <2 x i8> v1, v2
+  /// The possible mapping could be:
+  ///
+  /// {/*ID*/VectorAdd, /*Cost*/1, /*v0*/{(0xFFFF, VPR)}, /*v1*/{(0xFFFF, VPR)},
+  ///                              /*v2*/{(0xFFFF, VPR)}}
+  /// {/*ID*/ScalarAddx2, /*Cost*/2, /*v0*/{(0x00FF, GPR),(0xFF00, GPR)},
+  ///                                /*v1*/{(0x00FF, GPR),(0xFF00, GPR)},
+  ///                                /*v2*/{(0x00FF, GPR),(0xFF00, GPR)}}
+  ///
+  /// \note The first alternative of the returned mapping should be the
+  /// direct translation of \p MI current form.
+  ///
+  /// \post !returnedVal.empty().
+  InstructionMappings getInstrPossibleMappings(const MachineInstr &MI) const {
+    InstructionMappings PossibleMappings;
+    // Put the default mapping first.
+    PossibleMappings.push_back(getInstrMapping(MI));
+    // Then the alternative mapping, if any.
+    InstructionMappings AltMappings = getInstrAlternativeMappings(MI);
+    for (InstructionMapping &AltMapping : AltMappings)
+      PossibleMappings.emplace_back(std::move(AltMapping));
+#ifndef NDEBUG
+    for (const InstructionMapping &Mapping : PossibleMappings)
+      Mapping.verify(MI);
+#endif
+    return PossibleMappings;
+  }
+
   void verify(const TargetRegisterInfo &TRI) const;
 };
 

lib/CodeGen/GlobalISel/RegisterBankInfo.cpp

@@ -19,6 +19,7 @@
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetOpcodes.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 
 #include <algorithm> // For std::max.
@@ -27,6 +28,8 @@
 
 using namespace llvm;
 
+const unsigned RegisterBankInfo::DefaultMappingID = UINT_MAX;
+
 RegisterBankInfo::RegisterBankInfo(unsigned NumRegBanks)
     : NumRegBanks(NumRegBanks) {
   RegBanks.reset(new RegisterBank[NumRegBanks]);
@@ -176,6 +179,14 @@ void RegisterBankInfo::addRegBankCoverage(unsigned ID, unsigned RCId,
   } while (!WorkList.empty());
 }
 
+RegisterBankInfo::InstructionMapping
+RegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
+  if (MI.getOpcode() > TargetOpcode::GENERIC_OP_END) {
+    // TODO.
+  }
+  llvm_unreachable("The target must implement this");
+}
+
 //------------------------------------------------------------------------------
 // Helper classes implementation.
 //------------------------------------------------------------------------------