[LV] Remove unused configuration option (#82955)

Recent set of changes (PR #67725) in loop interleaving algorithm caused removal of the loop trip count threshold for allowing interleaving. Therefore configuration option interleave-small-loop-scalar-reduction is no longer needed.

Author: nilanjana87

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -315,12 +315,6 @@ static cl::opt<bool> EnableLoadStoreRuntimeInterleave(
     cl::desc(
         "Enable runtime interleaving until load/store ports are saturated"));
 
-/// Interleave small loops with scalar reductions.
-static cl::opt<bool> InterleaveSmallLoopScalarReduction(
-    "interleave-small-loop-scalar-reduction", cl::init(false), cl::Hidden,
-    cl::desc("Enable interleaving for loops with small iteration counts that "
-             "contain scalar reductions to expose ILP."));
-
 /// The number of stores in a loop that are allowed to need predication.
 static cl::opt<unsigned> NumberOfStoresToPredicate(
     "vectorize-num-stores-pred", cl::init(1), cl::Hidden,
@@ -5495,8 +5489,7 @@ LoopVectorizationCostModel::selectInterleaveCount(ElementCount VF,
 
     // If there are scalar reductions and TTI has enabled aggressive
     // interleaving for reductions, we will interleave to expose ILP.
-    if (InterleaveSmallLoopScalarReduction && VF.isScalar() &&
-        AggressivelyInterleaveReductions) {
+    if (VF.isScalar() && AggressivelyInterleaveReductions) {
       LLVM_DEBUG(dbgs() << "LV: Interleaving to expose ILP.\n");
       // Interleave no less than SmallIC but not as aggressive as the normal IC
       // to satisfy the rare situation when resources are too limited.

llvm/test/Transforms/LoopVectorize/PowerPC/interleave_IC.ll

@@ -1,5 +1,5 @@
-; RUN: opt < %s -passes=loop-vectorize -S -mcpu=pwr9 -interleave-small-loop-scalar-reduction=true 2>&1 | FileCheck %s
-; RUN: opt < %s -passes='loop-vectorize' -S -mcpu=pwr9 -interleave-small-loop-scalar-reduction=true 2>&1 | FileCheck %s
+; RUN: opt < %s -passes=loop-vectorize -S -mcpu=pwr9 2>&1 | FileCheck %s
+; RUN: opt < %s -passes='loop-vectorize' -S -mcpu=pwr9 2>&1 | FileCheck %s
 
 ; CHECK-LABEL: vector.body
 ; CHECK: load double, ptr