Enable runtime unrolling with unroll pragma metadata

Enable runtime unrolling for loops with unroll count metadata ("#pragma unroll N")
and a runtime trip count. Also, do not unroll loops with unroll full metadata if the
loop has a runtime loop count. Previously, such loops would be unrolled with a
very large threshold (pragma-unroll-threshold) if runtime unrolled happened to be
enabled resulting in a very large (and likely unwise) unroll factor.

llvm-svn: 242047

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index 9e7558d9c45..d78db6c369b 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -840,8 +840,10 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
 
   // Reduce count based on the type of unrolling and the threshold values.
   unsigned OriginalCount = Count;
-  bool AllowRuntime = UserRuntime ? CurrentRuntime : UP.Runtime;
-  if (HasRuntimeUnrollDisablePragma(L)) {
+  bool AllowRuntime =
+      (PragmaCount > 0) || (UserRuntime ? CurrentRuntime : UP.Runtime);
+  // Don't unroll a runtime trip count loop with unroll full pragma.
+  if (HasRuntimeUnrollDisablePragma(L) || PragmaFullUnroll) {
     AllowRuntime = false;
   }
   if (Unrolling == Partial) {