[PATCH] D67690: [LV][NFC] Factor out calculation of "best" estimated trip count.

[Florian Hahn via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGa3ca7acb4fa2: [LV][NFC] Factor out calculation of "best" estimated trip count. (authored by fhahn).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D67690/new/

https://reviews.llvm.org/D67690

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp


Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -355,6 +355,29 @@
                            : ConstantFP::get(Ty, C);
 }
 
+/// Returns "best known" trip count for the specified loop \p L as defined by
+/// the following procedure:
+///   1) Returns exact trip count if it is known.
+///   2) Returns expected trip count according to profile data if any.
+///   3) Returns upper bound estimate if it is known.
+///   4) Returns None if all of the above failed.
+static Optional<unsigned> getSmallBestKnownTC(ScalarEvolution &SE, Loop *L) {
+  // Check if exact trip count is known.
+  if (unsigned ExpectedTC = SE.getSmallConstantTripCount(L))
+    return ExpectedTC;
+
+  // Check if there is an expected trip count available from profile data.
+  if (LoopVectorizeWithBlockFrequency)
+    if (auto EstimatedTC = getLoopEstimatedTripCount(L))
+      return EstimatedTC;
+
+  // Check if upper bound estimate is known.
+  if (unsigned ExpectedTC = SE.getSmallConstantMaxTripCount(L))
+    return ExpectedTC;
+
+  return None;
+}
+
 namespace llvm {
 
 /// InnerLoopVectorizer vectorizes loops which contain only one basic
@@ -7483,36 +7506,11 @@
                                         ORE, BFI, PSI, Hints);
 
   assert(L->empty() && "Inner loop expected.");
+
   // Check the loop for a trip count threshold: vectorize loops with a tiny trip
   // count by optimizing for size, to minimize overheads.
-  // Prefer constant trip counts over profile data, over upper bound estimate.
-  unsigned ExpectedTC = 0;
-  bool HasExpectedTC = false;
-  if (const SCEVConstant *ConstExits =
-      dyn_cast<SCEVConstant>(SE->getBackedgeTakenCount(L))) {
-    const APInt &ExitsCount = ConstExits->getAPInt();
-    // We are interested in small values for ExpectedTC. Skip over those that
-    // can't fit an unsigned.
-    if (ExitsCount.ult(std::numeric_limits<unsigned>::max())) {
-      ExpectedTC = static_cast<unsigned>(ExitsCount.getZExtValue()) + 1;
-      HasExpectedTC = true;
-    }
-  }
-  // ExpectedTC may be large because it's bound by a variable. Check
-  // profiling information to validate we should vectorize.
-  if (!HasExpectedTC && LoopVectorizeWithBlockFrequency) {
-    auto EstimatedTC = getLoopEstimatedTripCount(L);
-    if (EstimatedTC) {
-      ExpectedTC = *EstimatedTC;
-      HasExpectedTC = true;
-    }
-  }
-  if (!HasExpectedTC) {
-    ExpectedTC = SE->getSmallConstantMaxTripCount(L);
-    HasExpectedTC = (ExpectedTC > 0);
-  }
-
-  if (HasExpectedTC && ExpectedTC < TinyTripCountVectorThreshold) {
+  auto ExpectedTC = getSmallBestKnownTC(*SE, L);
+  if (ExpectedTC && *ExpectedTC < TinyTripCountVectorThreshold) {
     LLVM_DEBUG(dbgs() << "LV: Found a loop with a very small trip count. "
                       << "This loop is worth vectorizing only if no scalar "
                       << "iteration overheads are incurred.");


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