AArch64: Implement large offset path for loadaddrEvaluator()

This commit implements the path in AArch64 OMRMemoryReference for
handling offsets wider than 12 bits.
It is used by loadaddrEvaluator().

Signed-off-by: KONNO Kazuhiro <konno@jp.ibm.com>

compiler/aarch64/codegen/OMRMemoryReference.cpp

@@ -850,20 +850,34 @@ uint8_t *OMR::ARM64::MemoryReference::generateBinaryEncoding(TR::Instruction *cu
          }
       else
          {
-         // loadaddrEvaluator() uses addimmx in generateTrgMemInstruction
+         // loadaddrEvaluator() uses addimmx in generateTrg1MemInstruction
          TR_ASSERT(index == NULL, "MemoryReference with unexpected indexed form");
 
-         base->setRegisterFieldRN(wcursor);
-
          if (constantIsUnsignedImm12(displacement))
             {
             *wcursor |= (displacement & 0xfff) << 10; /* imm12 */
             cursor += ARM64_INSTRUCTION_LENGTH;
             }
          else
             {
-            TR_ASSERT_FATAL(false, "Offset is too large for specified instruction.");
+            TR_ASSERT(currentInstruction->getKind() == OMR::Instruction::IsTrg1Mem, "unexpected instruction kind");
+            TR::RealRegister *treg = toRealRegister(((TR::ARM64Trg1MemInstruction *)currentInstruction)->getTargetRegister());
+            // movzw treg, low16bit
+            // movkw treg, high16bit, LSL #16
+            // addx treg, basereg, treg, SXTW
+            *wcursor = TR::InstOpCode::getOpCodeBinaryEncoding(TR::InstOpCode::movzw) | ((displacement & 0xFFFF) << 5);
+            treg->setRegisterFieldRD(wcursor);
+            wcursor++;
+            *wcursor = TR::InstOpCode::getOpCodeBinaryEncoding(TR::InstOpCode::movkw) | ((((displacement >> 16) & 0xFFFF) | TR::MOV_LSL16) << 5);
+            treg->setRegisterFieldRD(wcursor);
+            wcursor++;
+            *wcursor = TR::InstOpCode::getOpCodeBinaryEncoding(TR::InstOpCode::addx) | (TR::EXT_SXTW << 13);
+            treg->setRegisterFieldRD(wcursor);
+            treg->setRegisterFieldRM(wcursor);
+            cursor += ARM64_INSTRUCTION_LENGTH * 3;
             }
+
+         base->setRegisterFieldRN(wcursor);
          }
       }
 
@@ -953,7 +967,7 @@ uint32_t OMR::ARM64::MemoryReference::estimateBinaryLength(TR::InstOpCode op)
             }
          else
             {
-            TR_ASSERT_FATAL(false, "Offset is too large for specified instruction.");
+            return ARM64_INSTRUCTION_LENGTH*3;
             }
          }
       }