[RegisterBankInfo] Implement a target independent version of

getInstrMapping.

This implementation requires that the target implemented
getRegBankFromRegClass.
Indeed, the implementation uses the register classes for the encoding
constraints for the instructions to deduce the mapping of a value.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@265624 91177308-0d34-0410-b5e6-96231b3b80d8

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/TargetInstrInfo.h"
 #include "llvm/Target/TargetOpcodes.h"
 #include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
@@ -214,7 +215,45 @@ void RegisterBankInfo::addRegBankCoverage(unsigned ID, unsigned RCId,
 RegisterBankInfo::InstructionMapping
 RegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
   if (MI.getOpcode() > TargetOpcode::GENERIC_OP_END) {
-    // TODO.
+    // This is a target specific opcode:
+    // The mapping of the registers is already available via the
+    // register class.
+    // Just map the register class to a register bank.
+    RegisterBankInfo::InstructionMapping Mapping(DefaultMappingID, /*Cost*/ 1,
+                                                 MI.getNumOperands());
+    const TargetSubtargetInfo &STI =
+        MI.getParent()->getParent()->getSubtarget();
+    const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
+    const TargetInstrInfo &TII = *STI.getInstrInfo();
+
+    for (unsigned OpIdx = 0, End = MI.getNumOperands(); OpIdx != End; ++OpIdx) {
+      const MachineOperand &MO = MI.getOperand(OpIdx);
+      if (!MO.getReg())
+        continue;
+      // Since this is a target instruction, the operand must have a register
+      // class constraint.
+      const TargetRegisterClass *RC =
+          MI.getRegClassConstraint(OpIdx, &TII, &TRI);
+      // Note: This cannot be a "dynamic" constraint like inline asm,
+      //       since inlineasm opcode is a generic opcode.
+      assert(RC && "Invalid encoding constraints for target instruction?");
+
+      // Build the value mapping.
+      const RegisterBank &RegBank = getRegBankFromRegClass(*RC);
+      unsigned RegSize = getSizeInBits(MI, OpIdx);
+      assert(RegSize <= RegBank.getSize() && "Register bank too small");
+      // Assume the value is mapped in one register that lives in the
+      // register bank that covers RC.
+      APInt Mask(RegSize, 0);
+      // The value is represented by all the bits.
+      Mask.flipAllBits();
+
+      // Create the mapping object.
+      ValueMapping ValMapping;
+      ValMapping.BreakDown.push_back(PartialMapping(Mask, RegBank));
+      Mapping.setOperandMapping(OpIdx, ValMapping);
+    }
+    return Mapping;
   }
   llvm_unreachable("The target must implement this");
 }