[PATCH] D28460: getLoopEstimatedTripCount should really be called getLoopEstimatedBackedgeTakeCount.

[Xin Tong via Phabricator via llvm-commits]

trentxintong created this revision.
trentxintong added reviewers: mkuper, danielcdh, davidxl.
trentxintong added a subscriber: llvm-commits.
Herald added a subscriber: mzolotukhin.

getLoopEstimatedTripCount should really be called getLoopEstimatedBackedgeTakeCount.


https://reviews.llvm.org/D28460

Files:
  include/llvm/Transforms/Utils/LoopUtils.h
  lib/Transforms/Scalar/LoopUnrollPass.cpp
  lib/Transforms/Utils/LoopUnrollPeel.cpp
  lib/Transforms/Utils/LoopUtils.cpp


Index: lib/Transforms/Utils/LoopUtils.cpp
===================================================================
--- lib/Transforms/Utils/LoopUtils.cpp
+++ lib/Transforms/Utils/LoopUtils.cpp
@@ -1068,7 +1068,7 @@
   return true;
 }
 
-Optional<unsigned> llvm::getLoopEstimatedTripCount(Loop *L) {
+Optional<unsigned> llvm::getLoopEstimatedBackedgeTakenCount(Loop *L) {
   // Only support loops with a unique exiting block, and a latch.
   if (!L->getExitingBlock())
     return None;
Index: lib/Transforms/Utils/LoopUnrollPeel.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnrollPeel.cpp
+++ lib/Transforms/Utils/LoopUnrollPeel.cpp
@@ -84,7 +84,9 @@
   // We only do this in the presence of profile information, since otherwise
   // our estimates of the trip count are not reliable enough.
   if (UP.AllowPeeling && L->getHeader()->getParent()->getEntryCount()) {
-    Optional<unsigned> PeelCount = getLoopEstimatedTripCount(L);
+    // We only peel backedge taken count # of times as the original loop
+    // body will become the last iteration.
+    Optional<unsigned> PeelCount = getLoopEstimatedBackedgeTakenCount(L);
     if (!PeelCount)
       return;
 
Index: lib/Transforms/Scalar/LoopUnrollPass.cpp
===================================================================
--- lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -850,8 +850,10 @@
   
   // Check if the runtime trip count is too small when profile is available.
   if (L->getHeader()->getParent()->getEntryCount()) {
-    if (auto ProfileTripCount = getLoopEstimatedTripCount(L)) {
-      if (*ProfileTripCount < FlatLoopTripCountThreshold)
+    auto ProfileBETakenCount = getLoopEstimatedBackedgeTakenCount(L);
+    if (ProfileBETakenCount) {
+      // Trip count == BE taken count + 1.
+      if (*ProfileBETakenCount + 1  < FlatLoopTripCountThreshold)
         return false;
       else
         UP.AllowExpensiveTripCount = true;
Index: include/llvm/Transforms/Utils/LoopUtils.h
===================================================================
--- include/llvm/Transforms/Utils/LoopUtils.h
+++ include/llvm/Transforms/Utils/LoopUtils.h
@@ -461,10 +461,10 @@
 void addStringMetadataToLoop(Loop *TheLoop, const char *MDString,
                              unsigned V = 0);
 
-/// \brief Get a loop's estimated trip count based on branch weight metadata.
-/// Returns 0 when the count is estimated to be 0, or None when a meaningful
-/// estimate can not be made.
-Optional<unsigned> getLoopEstimatedTripCount(Loop *L);
+/// \brief Get a loop's estimated BE taken count based on branch weight
+/// metadata. Returns 0 when the count is estimated to be 0, or None when a
+/// meaningful estimate can not be made.
+Optional<unsigned> getLoopEstimatedBackedgeTakenCount(Loop *L);
 
 /// Helper to consistently add the set of standard passes to a loop pass's \c
 /// AnalysisUsage.


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