[LIR] Set attributes on memset_pattern16.

"inferattrs" will deduce the attribute, but it will be too late for
many optimizations. Set it ourselves when creating the call.

Differential Revision: http://reviews.llvm.org/D17598

llvm-svn: 267762
diff --git a/llvm/test/Transforms/LoopIdiom/basic.ll b/llvm/test/Transforms/LoopIdiom/basic.ll
index e4a4722..4d584de 100644
--- a/llvm/test/Transforms/LoopIdiom/basic.ll
+++ b/llvm/test/Transforms/LoopIdiom/basic.ll
@@ -564,3 +564,7 @@
 ; CHECK-NEXT: call void @llvm.memset.p0i8.i64(i8* %X, i8 0, i64 10000, i32 1, i1 false)
 ; CHECK: ret void
 }
+
+; Validate that "memset_pattern" has the proper attributes.
+; CHECK: declare void @memset_pattern16(i8* nocapture, i8* nocapture readonly, i64) [[ATTRS:#[0-9]+]]
+; CHECK: [[ATTRS]] = { argmemonly }