Enable partial and runtime loop unrolling for NVPTX.

Enable partial and runtime loop unrolling for NVPTX backend via
TTI::UnrollingPreferences with a small threshold. This partially unrolls
small loops which are often unrolled by the PTX to SASS compiler
and unrolling earlier can be beneficial.

llvm-svn: 242049

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp b/llvm/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp
index 241b145f719..e7250cdba5a 100644
--- a/llvm/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp
+++ b/llvm/lib/Target/NVPTX/NVPTXTargetTransformInfo.cpp
@@ -117,3 +117,15 @@ unsigned NVPTXTTIImpl::getArithmeticInstrCost(
                                          Opd1PropInfo, Opd2PropInfo);
   }
 }
+
+void NVPTXTTIImpl::getUnrollingPreferences(Loop *L,
+                                           TTI::UnrollingPreferences &UP) {
+  BaseT::getUnrollingPreferences(L, UP);
+
+  // Enable partial unrolling and runtime unrolling, but reduce the
+  // threshold.  This partially unrolls small loops which are often
+  // unrolled by the PTX to SASS compiler and unrolling earlier can be
+  // beneficial.
+  UP.Partial = UP.Runtime = true;
+  UP.PartialThreshold = UP.Threshold / 4;
+}