[llvm] 1678489 - [LV] FoldTail w/o Primary Induction
Ayal Zaks via llvm-commits
llvm-commits at lists.llvm.org
Thu Apr 9 07:51:40 PDT 2020
Author: Ayal Zaks
Date: 2020-04-09T17:45:23+03:00
New Revision: 16784892347b213da1d53bc05f59984d66dd014d
URL: https://github.com/llvm/llvm-project/commit/16784892347b213da1d53bc05f59984d66dd014d
DIFF: https://github.com/llvm/llvm-project/commit/16784892347b213da1d53bc05f59984d66dd014d.diff
LOG: [LV] FoldTail w/o Primary Induction
Introduce a new VPWidenCanonicalIVRecipe to generate a canonical vector
induction for use in fold-tail-with-masking, if a primary induction is absent.
The canonical scalar IV having start = 0 and step = VF*UF, created during code
-gen to control the vector loop, is widened into a canonical vector IV having
start = {<Part*VF, Part*VF+1, ..., Part*VF+VF-1> for 0 <= Part < UF} and
step = <VF*UF, VF*UF, ..., VF*UF>.
Differential Revision: https://reviews.llvm.org/D77635
Added:
Modified:
llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
llvm/lib/Transforms/Vectorize/VPlan.cpp
llvm/lib/Transforms/Vectorize/VPlan.h
llvm/test/Transforms/LoopVectorize/X86/small-size.ll
llvm/test/Transforms/LoopVectorize/tail-folding-counting-down.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
index 30182ce08abc..0eefa78915b3 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorizationLegality.cpp
@@ -1233,15 +1233,6 @@ bool LoopVectorizationLegality::prepareToFoldTailByMasking() {
LLVM_DEBUG(dbgs() << "LV: checking if tail can be folded by masking.\n");
- if (!PrimaryInduction) {
- reportVectorizationFailure(
- "No primary induction, cannot fold tail by masking",
- "Missing a primary induction variable in the loop, which is "
- "needed in order to fold tail by masking as required.",
- "NoPrimaryInduction", ORE, TheLoop);
- return false;
- }
-
SmallPtrSet<const Value *, 8> ReductionLiveOuts;
for (auto &Reduction : getReductionVars())
diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index d41e9c37bc01..49968ee0adcf 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -6585,6 +6585,7 @@ void LoopVectorizationPlanner::executePlan(InnerLoopVectorizer &ILV,
&ILV, CallbackILV};
State.CFG.PrevBB = ILV.createVectorizedLoopSkeleton();
State.TripCount = ILV.getOrCreateTripCount(nullptr);
+ State.CanonicalIV = ILV.Induction;
//===------------------------------------------------===//
//
@@ -6771,7 +6772,15 @@ VPValue *VPRecipeBuilder::createBlockInMask(BasicBlock *BB, VPlanPtr &Plan) {
// Introduce the early-exit compare IV <= BTC to form header block mask.
// This is used instead of IV < TC because TC may wrap, unlike BTC.
- VPValue *IV = Plan->getVPValue(Legal->getPrimaryInduction());
+ // Start by constructing the desired canonical IV.
+ VPValue *IV = nullptr;
+ if (Legal->getPrimaryInduction())
+ IV = Plan->getVPValue(Legal->getPrimaryInduction());
+ else {
+ auto IVRecipe = new VPWidenCanonicalIVRecipe();
+ Builder.getInsertBlock()->appendRecipe(IVRecipe);
+ IV = IVRecipe->getVPValue();
+ }
VPValue *BTC = Plan->getOrCreateBackedgeTakenCount();
BlockMask = Builder.createNaryOp(VPInstruction::ICmpULE, {IV, BTC});
return BlockMaskCache[BB] = BlockMask;
@@ -7130,12 +7139,13 @@ void LoopVectorizationPlanner::buildVPlansWithVPRecipes(unsigned MinVF,
NeedDef.insert(Branch->getCondition());
}
- // If the tail is to be folded by masking, the primary induction variable
- // needs to be represented in VPlan for it to model early-exit masking.
+ // If the tail is to be folded by masking, the primary induction variable, if
+ // exists needs to be represented in VPlan for it to model early-exit masking.
// Also, both the Phi and the live-out instruction of each reduction are
// required in order to introduce a select between them in VPlan.
if (CM.foldTailByMasking()) {
- NeedDef.insert(Legal->getPrimaryInduction());
+ if (Legal->getPrimaryInduction())
+ NeedDef.insert(Legal->getPrimaryInduction());
for (auto &Reduction : Legal->getReductionVars()) {
NeedDef.insert(Reduction.first);
NeedDef.insert(Reduction.second.getLoopExitInstr());
@@ -7572,9 +7582,8 @@ static ScalarEpilogueLowering getScalarEpilogueLowering(
!PreferPredicateOverEpilog;
// 2) Next, if disabling predication is requested on the command line, honour
- // this and request a scalar epilogue. Also do this if we don't have a
- // primary induction variable, which is required for predication.
- if (PredicateOptDisabled || !LVL.getPrimaryInduction())
+ // this and request a scalar epilogue.
+ if (PredicateOptDisabled)
return CM_ScalarEpilogueAllowed;
// 3) and 4) look if enabling predication is requested on the command line,
diff --git a/llvm/lib/Transforms/Vectorize/VPlan.cpp b/llvm/lib/Transforms/Vectorize/VPlan.cpp
index 17b4a3da6a06..dab4cbbd2423 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlan.cpp
@@ -802,6 +802,29 @@ void VPWidenMemoryInstructionRecipe::print(raw_ostream &O, const Twine &Indent,
O << "\\l\"";
}
+void VPWidenCanonicalIVRecipe::execute(VPTransformState &State) {
+ Value *CanonicalIV = State.CanonicalIV;
+ Type *STy = CanonicalIV->getType();
+ IRBuilder<> Builder(State.CFG.PrevBB->getTerminator());
+ Value *VStart = Builder.CreateVectorSplat(State.VF, CanonicalIV, "broadcast");
+ for (unsigned Part = 0, UF = State.UF; Part < UF; ++Part) {
+ SmallVector<Constant *, 8> Indices;
+ for (unsigned Lane = 0, VF = State.VF; Lane < VF; ++Lane)
+ Indices.push_back(ConstantInt::get(STy, Part * VF + Lane));
+ Constant *VStep = ConstantVector::get(Indices);
+ // Add the consecutive indices to the vector value.
+ Value *CanonicalVectorIV = Builder.CreateAdd(VStart, VStep, "vec.iv");
+ State.set(getVPValue(), CanonicalVectorIV, Part);
+ }
+}
+
+void VPWidenCanonicalIVRecipe::print(raw_ostream &O, const Twine &Indent,
+ VPSlotTracker &SlotTracker) const {
+ O << " +\n" << Indent << "\"EMIT ";
+ getVPValue()->printAsOperand(O, SlotTracker);
+ O << " = WIDEN-CANONICAL-INDUCTION \\l\"";
+}
+
template void DomTreeBuilder::Calculate<VPDominatorTree>(VPDominatorTree &DT);
void VPValue::replaceAllUsesWith(VPValue *New) {
@@ -901,6 +924,8 @@ void VPSlotTracker::assignSlots(const VPBasicBlock *VPBB) {
for (const VPRecipeBase &Recipe : *VPBB) {
if (const auto *VPI = dyn_cast<VPInstruction>(&Recipe))
assignSlot(VPI);
+ else if (const auto *VPIV = dyn_cast<VPWidenCanonicalIVRecipe>(&Recipe))
+ assignSlot(VPIV->getVPValue());
}
}
diff --git a/llvm/lib/Transforms/Vectorize/VPlan.h b/llvm/lib/Transforms/Vectorize/VPlan.h
index ed59f6e61b67..55c0754b9f95 100644
--- a/llvm/lib/Transforms/Vectorize/VPlan.h
+++ b/llvm/lib/Transforms/Vectorize/VPlan.h
@@ -329,6 +329,9 @@ struct VPTransformState {
/// Values they correspond to.
VPValue2ValueTy VPValue2Value;
+ /// Hold the canonical scalar IV of the vector loop (start=0, step=VF*UF).
+ Value *CanonicalIV = nullptr;
+
/// Hold the trip count of the scalar loop.
Value *TripCount = nullptr;
@@ -610,6 +613,7 @@ class VPRecipeBase : public ilist_node_with_parent<VPRecipeBase, VPBasicBlock> {
VPPredInstPHISC,
VPReplicateSC,
VPWidenCallSC,
+ VPWidenCanonicalIVSC,
VPWidenGEPSC,
VPWidenIntOrFpInductionSC,
VPWidenMemoryInstructionSC,
@@ -1144,6 +1148,36 @@ class VPWidenMemoryInstructionRecipe : public VPRecipeBase {
VPSlotTracker &SlotTracker) const override;
};
+/// A Recipe for widening the canonical induction variable of the vector loop.
+class VPWidenCanonicalIVRecipe : public VPRecipeBase {
+private:
+ /// A VPValue representing the canonical vector IV.
+ VPValue Val;
+
+public:
+ VPWidenCanonicalIVRecipe() : VPRecipeBase(VPWidenCanonicalIVSC) {}
+ ~VPWidenCanonicalIVRecipe() override = default;
+
+ /// Return the VPValue representing the canonical vector induction variable of
+ /// the vector loop.
+ const VPValue *getVPValue() const { return &Val; }
+ VPValue *getVPValue() { return &Val; }
+
+ /// Method to support type inquiry through isa, cast, and dyn_cast.
+ static inline bool classof(const VPRecipeBase *V) {
+ return V->getVPRecipeID() == VPRecipeBase::VPWidenCanonicalIVSC;
+ }
+
+ /// Generate a canonical vector induction variable of the vector loop, with
+ /// start = {<Part*VF, Part*VF+1, ..., Part*VF+VF-1> for 0 <= Part < UF}, and
+ /// step = <VF*UF, VF*UF, ..., VF*UF>.
+ void execute(VPTransformState &State) override;
+
+ /// Print the recipe.
+ void print(raw_ostream &O, const Twine &Indent,
+ VPSlotTracker &SlotTracker) const override;
+};
+
/// VPBasicBlock serves as the leaf of the Hierarchical Control-Flow Graph. It
/// holds a sequence of zero or more VPRecipe's each representing a sequence of
/// output IR instructions.
diff --git a/llvm/test/Transforms/LoopVectorize/X86/small-size.ll b/llvm/test/Transforms/LoopVectorize/X86/small-size.ll
index d54956edff33..c87b5dfc14db 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/small-size.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/small-size.ll
@@ -168,9 +168,17 @@ define void @example2(i32 %n, i32 %x) optsize {
ret void
}
-; N is unknown, we need a tail. Can't vectorize because loop has no primary
-; induction.
+; Loop has no primary induction as its integer IV has step -1 starting at
+; unknown N, but can still be vectorized.
;CHECK-LABEL: @example3(
+; CHECK: vector.ph:
+; CHECK: [[BROADCAST_SPLAT2:%.*]] = shufflevector <4 x i64> {{.*}}, <4 x i64> undef, <4 x i32> zeroinitializer
+; CHECK: vector.body:
+; CHECK-NEXT: [[INDEX:%.*]] = phi i64 [ 0,
+; CHECK-NEXT: [[BROADCAST_SPLATINSERT:%.*]] = insertelement <4 x i64> undef, i64 [[INDEX]], i32 0
+; CHECK-NEXT: [[BROADCAST_SPLAT:%.*]] = shufflevector <4 x i64> [[BROADCAST_SPLATINSERT]], <4 x i64> undef, <4 x i32> zeroinitializer
+; CHECK-NEXT: [[VPIV:%.*]] = or <4 x i64> [[BROADCAST_SPLAT]], <i64 0, i64 1, i64 2, i64 3>
+; CHECK: {{.*}} = icmp ule <4 x i64> [[VPIV]], [[BROADCAST_SPLAT2]]
;CHECK-NOT: <4 x i32>
;CHECK: ret void
define void @example3(i32 %n, i32* noalias nocapture %p, i32* noalias nocapture %q) optsize {
@@ -237,12 +245,12 @@ define void @example23b(i16* noalias nocapture %src, i32* noalias nocapture %dst
; CHECK-NEXT: store <4 x i32> [[TMP3]], <4 x i32>* [[TMP4]], align 4
; CHECK-NEXT: [[INDEX_NEXT]] = add i64 [[INDEX]], 4
; CHECK-NEXT: [[TMP5:%.*]] = icmp eq i64 [[INDEX_NEXT]], 256
-; CHECK-NEXT: br i1 [[TMP5]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop !6
+; CHECK-NEXT: br i1 [[TMP5]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop !10
; CHECK: middle.block:
; CHECK-NEXT: br i1 true, label [[TMP7:%.*]], label [[SCALAR_PH]]
; CHECK: scalar.ph:
; CHECK-NEXT: br label [[TMP6:%.*]]
-; CHECK: br i1 undef, label [[TMP7]], label [[TMP6]], !llvm.loop !7
+; CHECK: br i1 undef, label [[TMP7]], label [[TMP6]], !llvm.loop !11
; CHECK: ret void
;
br label %1
@@ -353,12 +361,12 @@ define void @example23c(i16* noalias nocapture %src, i32* noalias nocapture %dst
; CHECK: pred.store.continue22:
; CHECK-NEXT: [[INDEX_NEXT]] = add i64 [[INDEX]], 4
; CHECK-NEXT: [[TMP32:%.*]] = icmp eq i64 [[INDEX_NEXT]], 260
-; CHECK-NEXT: br i1 [[TMP32]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop !8
+; CHECK-NEXT: br i1 [[TMP32]], label [[MIDDLE_BLOCK:%.*]], label [[VECTOR_BODY]], !llvm.loop !12
; CHECK: middle.block:
; CHECK-NEXT: br i1 true, label [[TMP34:%.*]], label [[SCALAR_PH]]
; CHECK: scalar.ph:
; CHECK-NEXT: br label [[TMP33:%.*]]
-; CHECK: br i1 undef, label [[TMP34]], label [[TMP33]], !llvm.loop !9
+; CHECK: br i1 undef, label [[TMP34]], label [[TMP33]], !llvm.loop !13
; CHECK: ret void
;
br label %1
diff --git a/llvm/test/Transforms/LoopVectorize/tail-folding-counting-down.ll b/llvm/test/Transforms/LoopVectorize/tail-folding-counting-down.ll
index 2667bfe68f61..b51cb56045bf 100644
--- a/llvm/test/Transforms/LoopVectorize/tail-folding-counting-down.ll
+++ b/llvm/test/Transforms/LoopVectorize/tail-folding-counting-down.ll
@@ -1,12 +1,11 @@
-; RUN: opt < %s -loop-vectorize -prefer-predicate-over-epilog -S | FileCheck %s
+; RUN: opt < %s -loop-vectorize -prefer-predicate-over-epilog -force-vector-width=4 -S | FileCheck %s
-; Check that when we can't predicate this loop that it is still vectorised (with
-; an epilogue).
-; TODO: the reason this can't be predicated is because a primary induction
-; variable can't be found (not yet) for this counting down loop. But with that
-; fixed, this should be able to be predicated.
+; Check that a counting-down loop which has no primary induction variable
+; is vectorized with preferred predication.
; CHECK-LABEL: vector.body:
+; CHECK-LABEL: middle.block:
+; CHECK-NEXT: br i1 true,
target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
More information about the llvm-commits
mailing list