AArch64: Allow negative immediate offset for memory access

This commit rewrites the instruction "ldrimmw" (12-bit unsigned offset) to "ldur" (9-bit signed offset) when a negative value is used as the offset. Signed-off-by: KONNO Kazuhiro <konno@jp.ibm.com>
eclipse-omr · Dec 3, 2019 · d436fa9 · d436fa9
1 parent 8093d43
commit d436fa9
Showing 1 changed file with 18 additions and 2 deletions.
diff --git a/compiler/aarch64/codegen/OMRMemoryReference.cpp b/compiler/aarch64/codegen/OMRMemoryReference.cpp
@@ -824,7 +824,16 @@ uint8_t *OMR::ARM64::MemoryReference::generateBinaryEncoding(TR::Instruction *cu
                   }
                else
                   {
-                  TR_ASSERT(false, "Offset is too large for specified instruction.");
+                  if (op.getMnemonic() == TR::InstOpCode::ldrimmw && displacement < 0 && constantIsImm9(displacement))
+                     {
+                     *wcursor &= 0xFEFFFFFF; /* rewrite the instruction ldrimmw -> ldurw */
+                     *wcursor |= (displacement & 0x1ff) << 12; /* imm9 */
+                     cursor += ARM64_INSTRUCTION_LENGTH;
+                     }
+                  else
+                     {
+                     TR_ASSERT(false, "Offset is too large for specified instruction.");
+                     }
                   }
                }
             else if (isExclusiveMemAccessInstruction(op.getMnemonic()))
@@ -910,7 +919,14 @@ uint32_t OMR::ARM64::MemoryReference::estimateBinaryLength(TR::InstOpCode op)
                   }
                else
                   {
-                  TR_ASSERT(false, "Offset is too large for specified instruction.");
+                  if (op.getMnemonic() == TR::InstOpCode::ldrimmw && displacement < 0 && constantIsImm9(displacement))
+                     {
+                     return ARM64_INSTRUCTION_LENGTH;
+                     }
+                  else
+                     {
+                     TR_ASSERT(false, "Offset is too large for specified instruction.");
+                     }
                   }
                }
             else if (isExclusiveMemAccessInstruction(op.getMnemonic()))