[PATCH] Partial fix for bug 22589

[Sanjoy Das]

================
Comment at: lib/Transforms/Utils/LoopUnrollRuntime.cpp:124
@@ -118,1 +123,3 @@
+    new ICmpInst(InsertPt, ICmpInst::ICMP_ULT, BECount,
+                 ConstantInt::get(BECount->getType(), Count - 1));
   BasicBlock *Exit = L->getUniqueExitBlock();
----------------
majnemer wrote:
> If `Count` is `1`, then we are going to have `BECount u< 0`.  Is this possible? If not, we should assert.
I think that case is fine since if `Count` is `1` then we *should* unconditionally branch to the original loop.  The invariant (AFAICT!) is that we branch to the original loop when the number of iterations that remain is a multiple of `Count`.  That is always true for `Count == 1`.

I could add an assert but I'm not sure if there are edge cases where this code is called with `Count == 1`.

================
Comment at: lib/Transforms/Utils/LoopUnrollRuntime.cpp:322
@@ +321,3 @@
+  // BEWidth`.
+  if (static_cast<unsigned long long>(Count) > (1ULL << BEWidth))
+    return false;
----------------
majnemer wrote:
> Using `uint64_t` instead of `unsigned long long` might be a little more concise.
Will do.

http://reviews.llvm.org/D7715

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