[llvm] LV: reuse getSmallBestKnownTC in a TC estimation (NFC) (PR #105834)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/105834

>From 95d6bc043d1406de599f2bee353954f0d437dadd Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Fri, 23 Aug 2024 14:52:53 +0100
Subject: [PATCH 1/3] LV: reuse getSmallBestKnownTC in RT-check TC estimation

GeneratedRTChecks::getCost duplicates getSmallBestKnownTC partially,
when attempting to get the best trip-count estimate. Since the intent of
this code is to get the best trip-count estimate, and
getSmallBestKnownTC is written for exactly this purpose, replace the
partial code-duplication with a call to this function.
---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 0566d80c1cc001..687faa45f1d2c5 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -1961,14 +1961,9 @@ class GeneratedRTChecks {
           // count. Assume that the outer loop executes at least twice.
           unsigned BestTripCount = 2;
 
-          // If exact trip count is known use that.
-          if (unsigned SmallTC = SE->getSmallConstantTripCount(OuterLoop))
-            BestTripCount = SmallTC;
-          else if (LoopVectorizeWithBlockFrequency) {
-            // Else use profile data if available.
-            if (auto EstimatedTC = getLoopEstimatedTripCount(OuterLoop))
-              BestTripCount = *EstimatedTC;
-          }
+          // Get the best known TC estimate.
+          if (auto EstimatedTC = getSmallBestKnownTC(*SE, OuterLoop))
+            BestTripCount = *EstimatedTC;
 
           BestTripCount = std::max(BestTripCount, 1U);
           InstructionCost NewMemCheckCost = MemCheckCost / BestTripCount;

>From 9836b5b2270d7ee5b9b9843167442667ab051385 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Wed, 25 Sep 2024 13:05:17 +0100
Subject: [PATCH 2/3] LV: address review

---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 687faa45f1d2c5..1729e62e23406e 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -408,10 +408,11 @@ static bool hasIrregularType(Type *Ty, const DataLayout &DL) {
 /// 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.
+///   3) Returns upper bound estimate if known, and if CanUseConstantMax.
 ///   4) Returns std::nullopt if all of the above failed.
-static std::optional<unsigned> getSmallBestKnownTC(ScalarEvolution &SE,
-                                                   Loop *L) {
+static std::optional<unsigned>
+getSmallBestKnownTC(ScalarEvolution &SE, Loop *L,
+                    bool CanUseConstantMax = true) {
   // Check if exact trip count is known.
   if (unsigned ExpectedTC = SE.getSmallConstantTripCount(L))
     return ExpectedTC;
@@ -421,6 +422,9 @@ static std::optional<unsigned> getSmallBestKnownTC(ScalarEvolution &SE,
     if (auto EstimatedTC = getLoopEstimatedTripCount(L))
       return *EstimatedTC;
 
+  if (!CanUseConstantMax)
+    return std::nullopt;
+
   // Check if upper bound estimate is known.
   if (unsigned ExpectedTC = SE.getSmallConstantMaxTripCount(L))
     return ExpectedTC;
@@ -1962,7 +1966,8 @@ class GeneratedRTChecks {
           unsigned BestTripCount = 2;
 
           // Get the best known TC estimate.
-          if (auto EstimatedTC = getSmallBestKnownTC(*SE, OuterLoop))
+          if (auto EstimatedTC = getSmallBestKnownTC(
+                  *SE, OuterLoop, /* CanUseConstantMax = */ false))
             BestTripCount = *EstimatedTC;
 
           BestTripCount = std::max(BestTripCount, 1U);

>From 549452cc3ed81367e34948576e28c54c58452edf Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Mon, 30 Sep 2024 10:44:40 +0100
Subject: [PATCH 3/3] LV: fix nit

---
 llvm/lib/Transforms/Vectorize/LoopVectorize.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index 1729e62e23406e..61f3cc3500d02a 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -408,7 +408,7 @@ static bool hasIrregularType(Type *Ty, const DataLayout &DL) {
 /// 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 known, and if CanUseConstantMax.
+///   3) Returns upper bound estimate if known, and if \p CanUseConstantMax.
 ///   4) Returns std::nullopt if all of the above failed.
 static std::optional<unsigned>
 getSmallBestKnownTC(ScalarEvolution &SE, Loop *L,