MIPS: Support isLegalICmpImmediate and isLegalAddImmediate (#133400)

Set it to true only if isInt<16>.
By default implemention defines them to true always. For most cases,
MIPS uses 16bit IMM, and for microMIPS, ICMP and ADDiu have 16bit IMM
flavors.

Author: wzssyqa

llvm/lib/Target/Mips/MipsISelLowering.cpp

@@ -4474,6 +4474,14 @@ bool MipsTargetLowering::isFPImmLegal(const APFloat &Imm, EVT VT,
   return Imm.isZero();
 }
 
+bool MipsTargetLowering::isLegalICmpImmediate(int64_t Imm) const {
+  return isInt<16>(Imm);
+}
+
+bool MipsTargetLowering::isLegalAddImmediate(int64_t Imm) const {
+  return isInt<16>(Imm);
+}
+
 unsigned MipsTargetLowering::getJumpTableEncoding() const {
   if (!isPositionIndependent())
     return MachineJumpTableInfo::EK_BlockAddress;

llvm/lib/Target/Mips/MipsISelLowering.h

@@ -706,6 +706,9 @@ class TargetRegisterClass;
     bool isFPImmLegal(const APFloat &Imm, EVT VT,
                       bool ForCodeSize) const override;
 
+    bool isLegalICmpImmediate(int64_t Imm) const override;
+    bool isLegalAddImmediate(int64_t Imm) const override;
+
     unsigned getJumpTableEncoding() const override;
     SDValue getPICJumpTableRelocBase(SDValue Table,
                                      SelectionDAG &DAG) const override;