[llvm] Make 'UnrollMaxUpperBound' to be overridable by target. (PR #76029)

[via llvm-commits]

https://github.com/boxu-zhang updated https://github.com/llvm/llvm-project/pull/76029

>From 1a14ca997c52e3c6fb6b4153223c3bf209738686 Mon Sep 17 00:00:00 2001
From: "boxu.zhang" <boxu.zhang at hotmail.com>
Date: Wed, 20 Dec 2023 17:35:25 +0800
Subject: [PATCH] Make 'UnrollMaxUpperBound' to be overridable by target. The
 default value is still 8 and the command line argument
 '--unroll-max-upperbound' takes final effect if provided.

---
 llvm/include/llvm/Analysis/TargetTransformInfo.h | 4 ++++
 llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp    | 9 ++++++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/llvm/include/llvm/Analysis/TargetTransformInfo.h b/llvm/include/llvm/Analysis/TargetTransformInfo.h
index f5114fa40c70ad..735be3680aea0d 100644
--- a/llvm/include/llvm/Analysis/TargetTransformInfo.h
+++ b/llvm/include/llvm/Analysis/TargetTransformInfo.h
@@ -560,6 +560,10 @@ class TargetTransformInfo {
     // (set to UINT_MAX to disable). This does not apply in cases where the
     // loop is being fully unrolled.
     unsigned MaxCount;
+    /// Set the maximum upper bound of trip count. Allowing the MaxUpperBound
+    /// to be overrided by a target gives more flexiblity on certain cases.
+    /// By default, MaxUpperBound uses UnrollMaxUpperBound which value is 8.
+    unsigned MaxUpperBound;
     /// Set the maximum unrolling factor for full unrolling. Like MaxCount, but
     /// applies even if full unrolling is selected. This allows a target to fall
     /// back to Partial unrolling if full unrolling is above FullUnrollMaxCount.
diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index f14541a1a037e6..7cfeb019af9723 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -200,6 +200,7 @@ TargetTransformInfo::UnrollingPreferences llvm::gatherUnrollingPreferences(
   UP.Count = 0;
   UP.DefaultUnrollRuntimeCount = 8;
   UP.MaxCount = std::numeric_limits<unsigned>::max();
+  UP.MaxUpperBound = UnrollMaxUpperBound;
   UP.FullUnrollMaxCount = std::numeric_limits<unsigned>::max();
   UP.BEInsns = 2;
   UP.Partial = false;
@@ -237,6 +238,8 @@ TargetTransformInfo::UnrollingPreferences llvm::gatherUnrollingPreferences(
     UP.MaxPercentThresholdBoost = UnrollMaxPercentThresholdBoost;
   if (UnrollMaxCount.getNumOccurrences() > 0)
     UP.MaxCount = UnrollMaxCount;
+  if (UnrollMaxUpperBound.getNumOccurrences() > 0)
+    UP.MaxUpperBound = UnrollMaxUpperBound;
   if (UnrollFullMaxCount.getNumOccurrences() > 0)
     UP.FullUnrollMaxCount = UnrollFullMaxCount;
   if (UnrollAllowPartial.getNumOccurrences() > 0)
@@ -777,7 +780,7 @@ shouldPragmaUnroll(Loop *L, const PragmaInfo &PInfo,
     return TripCount;
 
   if (PInfo.PragmaEnableUnroll && !TripCount && MaxTripCount &&
-      MaxTripCount <= UnrollMaxUpperBound)
+      MaxTripCount <= UP.MaxUpperBound)
     return MaxTripCount;
 
   // if didn't return until here, should continue to other priorties
@@ -952,7 +955,7 @@ bool llvm::computeUnrollCount(
   // cost of exact full unrolling.  As such, if we have an exact count and
   // found it unprofitable, we'll never chose to bounded unroll.
   if (!TripCount && MaxTripCount && (UP.UpperBound || MaxOrZero) &&
-      MaxTripCount <= UnrollMaxUpperBound) {
+      MaxTripCount <= UP.MaxUpperBound) {
     UP.Count = MaxTripCount;
     if (auto UnrollFactor = shouldFullUnroll(L, TTI, DT, SE, EphValues,
                                              MaxTripCount, UCE, UP)) {
@@ -1026,7 +1029,7 @@ bool llvm::computeUnrollCount(
   }
 
   // Don't unroll a small upper bound loop unless user or TTI asked to do so.
-  if (MaxTripCount && !UP.Force && MaxTripCount < UnrollMaxUpperBound) {
+  if (MaxTripCount && !UP.Force && MaxTripCount < UP.MaxUpperBound) {
     UP.Count = 0;
     return false;
   }