[FastISel][AArch64] Fold offset into the memory operation.

Fold simple offsets into the memory operation:
  add x0, x0, #8
  ldr x0, [x0]
-->
  ldr x0, [x0, #8]

Fixes <rdar://problem/17887945>.

llvm-svn: 214545

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64FastISel.cpp b/llvm/lib/Target/AArch64/AArch64FastISel.cpp
index f748185bc95..8cfdab24651 100644
--- a/llvm/lib/Target/AArch64/AArch64FastISel.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FastISel.cpp
@@ -419,6 +419,13 @@ bool AArch64FastISel::ComputeAddress(const Value *Obj, Address &Addr) {
     }
     break;
   }
+  case Instruction::Add:
+    // Adds of constants are common and easy enough.
+    if (const ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1))) {
+      Addr.setOffset(Addr.getOffset() + (uint64_t)CI->getSExtValue());
+      return ComputeAddress(U->getOperand(0), Addr);
+    }
+    break;
   }
 
   // Try to get this in a register if nothing else has worked.