Enable disabled loopidiom test. Apparently we handle it now

[trentxintong]

Summary

Enable disabled loopidiom test. Apparently we handle it now.
Maybe due to improvements to AA.

[trentxintong]

Friendly ping.

[atrick]

Thanks Xin!

test/Transforms/LoopIdiom/basic.ll

 
 for.end:                                          ; preds = %entry
   ret void
 ; CHECK-LABEL: @test3(
 ; CHECK-NOT: memset
 ; CHECK: ret void
 }
 
-
-;; TODO: We should be able to promote this memset.  Not yet though.
+; Make sure the first store in the loop is turned into a memset.
 define void @test4(i8* %Base) nounwind ssp {
 bb.nph:                                           ; preds = %entry
   %Base100 = getelementptr i8, i8* %Base, i64 1000
   br label %for.body
 
 for.body:                                         ; preds = %bb.nph, %for.body
   %indvar = phi i64 [ 0, %bb.nph ], [ %indvar.next, %for.body ]
   %I.0.014 = getelementptr i8, i8* %Base, i64 %indvar
   store i8 0, i8* %I.0.014, align 1
   
   ;; Store beyond the range memset, should be safe to promote.
   store i8 42, i8* %Base100
   
   %indvar.next = add i64 %indvar, 1
   %exitcond = icmp eq i64 %indvar.next, 100
   br i1 %exitcond, label %for.end, label %for.body
 
 for.end:                                          ; preds = %for.body, %entry
   ret void
-; CHECK-TODO-LABEL: @test4(
-; CHECK-TODO: call void @llvm.memset.p0i8.i64(i8* %Base, i8 0, i64 100, i32 1, i1 false)
-; CHECK-TODO-NOT: store
+; CHECK-LABEL: @test4(
+; CHECK: call void @llvm.memset.p0i8.i64(i8* %Base, i8 0, i64 100, i32 1, i1 false)
 }
 
 ; This can't be promoted: the memset is a store of a loop variant value.
 define void @test5(i8* %Base, i64 %Size) nounwind ssp {
 bb.nph:                                           ; preds = %entry
   br label %for.body
 
 for.body:                                         ; preds = %bb.nph, %for.body