[SimpleLoopUnswitch] Allow threshold to be specified zero or more times

[aeubanks]

What's the motivation behind this?
In general I don't think we support this sort of -mllvm behavior.

[ctetreau]

In D110594#3026096, @aeubanks wrote:

What's the motivation behind this?
In general I don't think we support this sort of -mllvm behavior.

Internally, we have clang set this to override the default. Then, if the user tries to set it, they will get an error.

[ctetreau]

@aeubanks Sorry, I accidentally pushed this commit. Personally, I think it's fine and obvious (meeting the standards of merging without review), but if you still object let me know and I can revert it.

[aeubanks]

I still think it's kinda iffy, but not really a huge deal

llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp

 
 static cl::opt<bool> EnableNonTrivialUnswitch(
     "enable-nontrivial-unswitch", cl::init(false), cl::Hidden,
     cl::desc("Forcibly enables non-trivial loop unswitching rather than "
              "following the configuration passed into the pass."));
 
 static cl::opt<int>
     UnswitchThreshold("unswitch-threshold", cl::init(50), cl::Hidden,
+                      cl::ZeroOrMore,
                       cl::desc("The cost threshold for unswitching a loop."));
 
 static cl::opt<bool> EnableUnswitchCostMultiplier(
     "enable-unswitch-cost-multiplier", cl::init(true), cl::Hidden,
     cl::desc("Enable unswitch cost multiplier that prohibits exponential "
              "explosion in nontrivial unswitch."));
 static cl::opt<int> UnswitchSiblingsToplevelDiv(
     "unswitch-siblings-toplevel-div", cl::init(2), cl::Hidden,