[SimplifyCFG] remove bogus test case; NFC

[shawnl]

Summary

Even if one bit is defined, the code is not clear what it is suppose to do.

See 41530

[nikic]

Patch doesn't seem to be against master, here's how the test looks right now: https://github.com/llvm-mirror/llvm/blob/master/test/Transforms/SimplifyCFG/switch-dead-default.ll#L160

In any case, agree that the test doesn't make sense and we should drop it. The test wants to assert that some bits are undef, but that's not what the IR does and I don't think it's even possible to do that in any meaningful way. It was added in D12497, so @reames might want to double check.

[RKSimon]

@reames Do you have any objection to removing this test?

[RKSimon]

@reames Any final comments?

[reames]

In D60859#1526786, @RKSimon wrote:

@reames Any final comments?

None, feel free to kill it.

[RKSimon]

In D60859#1528116, @reames wrote:

In D60859#1526786, @RKSimon wrote:

@reames Any final comments?

None, feel free to kill it.

Thanks - LGTM

[thakis]

Most bots on the waterfall are unhappy after this, e.g. http://lab.llvm.org:8011/builders/clang-atom-d525-fedora-rel/builds/25030/steps/ninja%20check%201/logs/FAIL%3A%20LLVM%3A%3Aswitch-dead-default.ll -- can you fix quickly, or if it takes a while revert?

[nikic]

@thakis Looks like it got fixed in rL362501.

llvm/trunk/test/Transforms/SimplifyCFG/switch-dead-default.ll

false:
   ret void
 also_dead:
   call void @foo(i32 5)
   ret void
 default:
   call void @foo(i32 2)
   ret void
 }
-
-;; All but one bit known undef
-;; Note: This is currently testing an optimization which doesn't trigger. The
-;; case this is protecting against is that a bit could be assumed both zero 
-;; *or* one given we know it's undef.  ValueTracking doesn't do this today,
-;; but it doesn't hurt to confirm.
-define void @test8(i8 %a) {
-; CHECK-LABEL: @test8(
-; CHECK: switch i8
-  %and = and i8 %a, 254
-  %cmp = icmp eq i8 %and, undef
-  call void @llvm.assume(i1 %cmp)
-  switch i8 %a, label %default [i8 255, label %true
-                                i8 254, label %false]
-true:
-  call void @foo(i32 1)
-  ret void
-false:
-  call void @foo(i32 3)
-  ret void
-default:
-  call void @foo(i32 2)
-  ret void
-}
-
-declare void @llvm.assume(i1)