[llvm-branch-commits] [llvm] 0c2d239 - [SystemZTTIImpl] Allow some non-prefetched accesses in getMinPrefetchStride().

[Jonas Paulsson via llvm-branch-commits]

Author: Jonas Paulsson
Date: 2020-12-11T18:06:07-06:00
New Revision: 0c2d23933f06ed048191f84ecde889e9da93609c

URL: https://github.com/llvm/llvm-project/commit/0c2d23933f06ed048191f84ecde889e9da93609c
DIFF: https://github.com/llvm/llvm-project/commit/0c2d23933f06ed048191f84ecde889e9da93609c.diff

LOG: [SystemZTTIImpl] Allow some non-prefetched accesses in getMinPrefetchStride().

The performance improvement on LBM previously achieved with improved software
prefetching (36d4421) have gone lost recently with e00f189. There now is one
memory access in the loop that LoopDataPrefetch cannot handle (while before
there was none) which the heuristic rejects.

This patch adds a small margin by allowing 1 non-prefetched memory access for
every 32 prefetched ones, so that the heuristic doesn't bail in this type of
case.

Review: Ulrich Weigand

Differential Revision: https://reviews.llvm.org/D92985

Added: 
    

Modified: 
    llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp b/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
index 2c6659b79cc3..e7ac2391512f 100644
--- a/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZTargetTransformInfo.cpp
@@ -341,8 +341,8 @@ unsigned SystemZTTIImpl::getMinPrefetchStride(unsigned NumMemAccesses,
 
   // Emit prefetch instructions for smaller strides in cases where we think
   // the hardware prefetcher might not be able to keep up.
-  if (NumStridedMemAccesses > 32 &&
-      NumStridedMemAccesses == NumMemAccesses && !HasCall)
+  if (NumStridedMemAccesses > 32 && !HasCall &&
+      (NumMemAccesses - NumStridedMemAccesses) * 32 <= NumStridedMemAccesses)
     return 1;
 
   return ST->hasMiscellaneousExtensions3() ? 8192 : 2048;