[Constant Hoisting][ARM64] Enable constant hoisting for ARM64.

This implements the target-hooks for ARM64 to enable constant hoisting.

This fixes <rdar://problem/14774662> and <rdar://problem/16381500>.

llvm-svn: 205791
diff --git a/llvm/test/CodeGen/ARM64/const-addr.ll b/llvm/test/CodeGen/ARM64/const-addr.ll
new file mode 100644
index 0000000..c77a6db
--- /dev/null
+++ b/llvm/test/CodeGen/ARM64/const-addr.ll
@@ -0,0 +1,23 @@
+; RUN: llc -mtriple=arm64-darwin-unknown < %s | FileCheck %s
+
+%T = type { i32, i32, i32, i32 }
+
+; Test if the constant base address gets only materialized once.
+define i32 @test1() nounwind {
+; CHECK-LABEL:  test1
+; CHECK:        movz  x8, #1039, lsl #16
+; CHECK-NEXT:   movk  x8, #49152
+; CHECK-NEXT:   ldp w9, w10, [x8, #4]
+; CHECK:        ldr w8, [x8, #12]
+  %at = inttoptr i64 68141056 to %T*
+  %o1 = getelementptr %T* %at, i32 0, i32 1
+  %t1 = load i32* %o1
+  %o2 = getelementptr %T* %at, i32 0, i32 2
+  %t2 = load i32* %o2
+  %a1 = add i32 %t1, %t2
+  %o3 = getelementptr %T* %at, i32 0, i32 3
+  %t3 = load i32* %o3
+  %a2 = add i32 %a1, %t3
+  ret i32 %a2
+}
+