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[LV] Don't ignore invariant stores when costing #158682

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Merged
merged 1 commit into from
Sep 24, 2025
+18 −18
Merged

[LV] Don't ignore invariant stores when costing #158682

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14 changes: 0 additions & 14 deletions llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6367,19 +6367,8 @@ void LoopVectorizationCostModel::collectValuesToIgnore() {

LoopBlocksDFS DFS(TheLoop);
DFS.perform(LI);
MapVector<Value *, SmallVector<Value *>> DeadInvariantStoreOps;
for (BasicBlock *BB : reverse(make_range(DFS.beginRPO(), DFS.endRPO())))
for (Instruction &I : reverse(*BB)) {
// Find all stores to invariant variables. Since they are going to sink
// outside the loop we do not need calculate cost for them.
StoreInst *SI;
if ((SI = dyn_cast<StoreInst>(&I)) &&
Legal->isInvariantAddressOfReduction(SI->getPointerOperand())) {
ValuesToIgnore.insert(&I);
DeadInvariantStoreOps[SI->getPointerOperand()].push_back(
SI->getValueOperand());
}

if (VecValuesToIgnore.contains(&I) || ValuesToIgnore.contains(&I))
continue;

Expand Down Expand Up @@ -6426,9 +6415,6 @@ void LoopVectorizationCostModel::collectValuesToIgnore() {
append_range(DeadInterleavePointerOps, Op->operands());
}

for (const auto &[_, Ops] : DeadInvariantStoreOps)
llvm::append_range(DeadOps, drop_end(Ops));

// Mark ops that would be trivially dead and are only used by ignored
// instructions as free.
BasicBlock *Header = TheLoop->getHeader();
Expand Down
22 changes: 18 additions & 4 deletions llvm/test/Transforms/LoopVectorize/X86/invariant-store-vectorization.ll
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Expand Up @@ -398,16 +398,30 @@ for.end: ; preds = %for.body
define void @test_store_of_final_reduction_value(i64 %x, ptr %dst) {
; CHECK-LABEL: define void @test_store_of_final_reduction_value(
; CHECK-SAME: i64 [[X:%.*]], ptr [[DST:%.*]]) #[[ATTR0]] {
; CHECK-NEXT: [[ENTRY:.*]]:
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: br i1 false, label %[[SCALAR_PH:.*]], label %[[VECTOR_PH:.*]]
; CHECK: [[VECTOR_PH]]:
; CHECK-NEXT: [[BROADCAST_SPLATINSERT:%.*]] = insertelement <2 x i64> poison, i64 [[X]], i64 0
; CHECK-NEXT: [[BROADCAST_SPLAT:%.*]] = shufflevector <2 x i64> [[BROADCAST_SPLATINSERT]], <2 x i64> poison, <2 x i32> zeroinitializer
; CHECK-NEXT: br label %[[VECTOR_BODY:.*]]
; CHECK: [[VECTOR_BODY]]:
; CHECK-NEXT: [[VEC_PHI:%.*]] = phi <2 x i64> [ <i64 0, i64 1>, %[[VECTOR_PH]] ], [ [[TMP0:%.*]], %[[VECTOR_BODY]] ]
; CHECK-NEXT: [[TMP0]] = mul <2 x i64> [[VEC_PHI]], [[BROADCAST_SPLAT]]
; CHECK-NEXT: br i1 true, label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP32:![0-9]+]]
; CHECK: [[MIDDLE_BLOCK]]:
; CHECK-NEXT: [[TMP1:%.*]] = call i64 @llvm.vector.reduce.mul.v2i64(<2 x i64> [[TMP0]])
; CHECK-NEXT: store i64 [[TMP1]], ptr [[DST]], align 8
; CHECK-NEXT: br label %[[EXIT:.*]]
; CHECK: [[SCALAR_PH]]:
; CHECK-NEXT: br label %[[LOOP:.*]]
; CHECK: [[LOOP]]:
; CHECK-NEXT: [[IV4:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[RED:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[RED_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[IV4:%.*]] = phi i64 [ 0, %[[SCALAR_PH]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[RED:%.*]] = phi i64 [ 0, %[[SCALAR_PH]] ], [ [[RED_NEXT:%.*]], %[[LOOP]] ]
; CHECK-NEXT: [[RED_NEXT]] = mul i64 [[RED]], [[X]]
; CHECK-NEXT: store i64 [[RED_NEXT]], ptr [[DST]], align 8
; CHECK-NEXT: [[IV_NEXT]] = add i64 [[IV4]], 1
; CHECK-NEXT: [[EC:%.*]] = icmp eq i64 [[IV4]], 1
; CHECK-NEXT: br i1 [[EC]], label %[[EXIT:.*]], label %[[LOOP]]
; CHECK-NEXT: br i1 [[EC]], label %[[EXIT]], label %[[LOOP]], !llvm.loop [[LOOP33:![0-9]+]]
; CHECK: [[EXIT]]:
; CHECK-NEXT: ret void
;
Expand Down