[LoopUnroll] Use LoopSize+1 as threshold, to allow unrolling loops matching LoopSize.

We use `< UP.Threshold` later on, so we should use LoopSize + 1, to
allow unrolling if the result won't exceed to loop size.

Fixes PR43305.

Reviewers: efriedma, dmgreen, paquette

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D67594

llvm-svn: 372084

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index d52ce9e815b..244c7d15192 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -1032,10 +1032,10 @@ static LoopUnrollResult tryToUnrollLoop(
     return LoopUnrollResult::Unmodified;
   }
 
-  // When optimizing for size, use LoopSize as threshold, to (fully) unroll
-  // loops, if it does not increase code size.
+  // When optimizing for size, use LoopSize + 1 as threshold (we use < Threshold
+  // later), to (fully) unroll loops, if it does not increase code size.
   if (OptForSize)
-    UP.Threshold = std::max(UP.Threshold, LoopSize);
+    UP.Threshold = std::max(UP.Threshold, LoopSize + 1);
 
   if (NumInlineCandidates != 0) {
     LLVM_DEBUG(dbgs() << "  Not unrolling loop with inlinable calls.\n");