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Revert "[SLP] Truncate expressions to minimum required bit width"

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This reverts commit r258404.

llvm-svn: 258408
This commit is contained in:
Matthew Simpson 2016-01-21 17:17:20 +00:00
parent 1a124a3e27
commit d8f9568a4c
2 changed files with 24 additions and 161 deletions
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154
lib/Transforms/Vectorize/SLPVectorizer.cpp
View File

@ -15,22 +15,21 @@
// "Loop-Aware SLP in GCC" by Ira Rosen, Dorit Nuzman, Ayal Zaks.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Vectorize.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/PostOrderIterator.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/DemandedBits.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Analysis/VectorUtils.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
@ -45,7 +44,7 @@
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Vectorize.h"
#include "llvm/Analysis/VectorUtils.h"
#include <algorithm>
#include <map>
#include <memory>
@ -364,12 +363,11 @@ public:
BoUpSLP(Function *Func, ScalarEvolution *Se, TargetTransformInfo *Tti,
TargetLibraryInfo *TLi, AliasAnalysis *Aa, LoopInfo *Li,
DominatorTree *Dt, AssumptionCache *AC, DemandedBits *DB)
DominatorTree *Dt, AssumptionCache *AC)
: NumLoadsWantToKeepOrder(0), NumLoadsWantToChangeOrder(0), F(Func),
SE(Se), TTI(Tti), TLI(TLi), AA(Aa), LI(Li), DT(Dt), AC(AC), DB(DB),
SE(Se), TTI(Tti), TLI(TLi), AA(Aa), LI(Li), DT(Dt),
Builder(Se->getContext()) {
CodeMetrics::collectEphemeralValues(F, AC, EphValues);
MaxRequiredIntegerTy = nullptr;
}
/// \brief Vectorize the tree that starts with the elements in \p VL.
@ -401,7 +399,6 @@ public:
BlockScheduling *BS = Iter.second.get();
BS->clear();
}
MaxRequiredIntegerTy = nullptr;
}
/// \returns true if the memory operations A and B are consecutive.
@ -422,10 +419,6 @@ public:
/// vectorization factors.
unsigned getVectorElementSize(Value *V);
/// Compute the maximum width integer type required to represent the result
/// of a scalar expression, if such a type exists.
void computeMaxRequiredIntegerTy();
private:
struct TreeEntry;
@ -931,13 +924,8 @@ private:
AliasAnalysis *AA;
LoopInfo *LI;
DominatorTree *DT;
AssumptionCache *AC;
DemandedBits *DB;
/// Instruction builder to construct the vectorized tree.
IRBuilder<> Builder;
// The maximum width integer type required to represent a scalar expression.
IntegerType *MaxRequiredIntegerTy;
};
#ifndef NDEBUG
@ -1493,15 +1481,6 @@ int BoUpSLP::getEntryCost(TreeEntry *E) {
ScalarTy = SI->getValueOperand()->getType();
VectorType *VecTy = VectorType::get(ScalarTy, VL.size());
// If we have computed a smaller type for the expression, update VecTy so
// that the costs will be accurate.
if (MaxRequiredIntegerTy) {
auto *IT = dyn_cast<IntegerType>(ScalarTy);
assert(IT && "Computed smaller type for non-integer value?");
if (MaxRequiredIntegerTy->getBitWidth() < IT->getBitWidth())
VecTy = VectorType::get(MaxRequiredIntegerTy, VL.size());
}
if (E->NeedToGather) {
if (allConstant(VL))
return 0;
@ -1830,17 +1809,9 @@ int BoUpSLP::getTreeCost() {
if (EphValues.count(EU.User))
continue;
// If we plan to rewrite the tree in a smaller type, we will need to sign
// extend the extracted value back to the original type. Here, we account
// for the extract and the added cost of the sign extend if needed.
auto *VecTy = VectorType::get(EU.Scalar->getType(), BundleWidth);
if (MaxRequiredIntegerTy) {
VecTy = VectorType::get(MaxRequiredIntegerTy, BundleWidth);
ExtractCost += TTI->getCastInstrCost(
Instruction::SExt, EU.Scalar->getType(), MaxRequiredIntegerTy);
}
ExtractCost +=
TTI->getVectorInstrCost(Instruction::ExtractElement, VecTy, EU.Lane);
VectorType *VecTy = VectorType::get(EU.Scalar->getType(), BundleWidth);
ExtractCost += TTI->getVectorInstrCost(Instruction::ExtractElement, VecTy,
EU.Lane);
}
Cost += getSpillCost();
@ -2595,19 +2566,7 @@ Value *BoUpSLP::vectorizeTree() {
}
Builder.SetInsertPoint(&F->getEntryBlock().front());
auto *VectorRoot = vectorizeTree(&VectorizableTree[0]);
// If the vectorized tree can be rewritten in a smaller type, we truncate the
// vectorized root. InstCombine will then rewrite the entire expression. We
// sign extend the extracted values below.
if (MaxRequiredIntegerTy) {
BasicBlock::iterator I(cast<Instruction>(VectorRoot));
Builder.SetInsertPoint(&*++I);
auto BundleWidth = VectorizableTree[0].Scalars.size();
auto *SmallerTy = VectorType::get(MaxRequiredIntegerTy, BundleWidth);
auto *Trunc = Builder.CreateTrunc(VectorRoot, SmallerTy);
VectorizableTree[0].VectorizedValue = Trunc;
}
vectorizeTree(&VectorizableTree[0]);
DEBUG(dbgs() << "SLP: Extracting " << ExternalUses.size() << " values .\n");
@ -2640,8 +2599,6 @@ Value *BoUpSLP::vectorizeTree() {
if (PH->getIncomingValue(i) == Scalar) {
Builder.SetInsertPoint(PH->getIncomingBlock(i)->getTerminator());
Value *Ex = Builder.CreateExtractElement(Vec, Lane);
if (MaxRequiredIntegerTy)
Ex = Builder.CreateSExt(Ex, Scalar->getType());
CSEBlocks.insert(PH->getIncomingBlock(i));
PH->setOperand(i, Ex);
}
@ -2649,16 +2606,12 @@ Value *BoUpSLP::vectorizeTree() {
} else {
Builder.SetInsertPoint(cast<Instruction>(User));
Value *Ex = Builder.CreateExtractElement(Vec, Lane);
if (MaxRequiredIntegerTy)
Ex = Builder.CreateSExt(Ex, Scalar->getType());
CSEBlocks.insert(cast<Instruction>(User)->getParent());
User->replaceUsesOfWith(Scalar, Ex);
}
} else {
Builder.SetInsertPoint(&F->getEntryBlock().front());
Value *Ex = Builder.CreateExtractElement(Vec, Lane);
if (MaxRequiredIntegerTy)
Ex = Builder.CreateSExt(Ex, Scalar->getType());
CSEBlocks.insert(&F->getEntryBlock());
User->replaceUsesOfWith(Scalar, Ex);
}
@ -3227,7 +3180,7 @@ unsigned BoUpSLP::getVectorElementSize(Value *V) {
// If the current instruction is a load, update MaxWidth to reflect the
// width of the loaded value.
else if (isa<LoadInst>(I))
MaxWidth = std::max<unsigned>(MaxWidth, DL.getTypeSizeInBits(Ty));
MaxWidth = std::max(MaxWidth, (unsigned)DL.getTypeSizeInBits(Ty));
// Otherwise, we need to visit the operands of the instruction. We only
// handle the interesting cases from buildTree here. If an operand is an
@ -3254,85 +3207,6 @@ unsigned BoUpSLP::getVectorElementSize(Value *V) {
return MaxWidth;
}
void BoUpSLP::computeMaxRequiredIntegerTy() {
// If there are no external uses, the expression tree must be rooted by a
// store. We can't demote in-memory values, so there is nothing to do here.
if (ExternalUses.empty())
return;
// If the expression is not rooted by a store, these roots should have
// external uses. We will rely on InstCombine to rewrite the expression in
// the narrower type. However, InstCombine only rewrites single-use values.
// This means that if a tree entry other than a root is used externally, it
// must have multiple uses and InstCombine will not rewrite it. The code
// below ensures that only the roots are used externally.
auto &TreeRoot = VectorizableTree[0].Scalars;
SmallPtrSet<Value *, 16> ScalarRoots(TreeRoot.begin(), TreeRoot.end());
for (auto &EU : ExternalUses)
if (!ScalarRoots.erase(EU.Scalar))
return;
if (!ScalarRoots.empty())
return;
// The maximum bit width required to represent all the instructions in the
// tree without loss of precision. It would be safe to truncate the
// expression to this width.
auto MaxBitWidth = 8u;
// We first check if all the bits of the root are demanded. If they're not,
// we can truncate the root to this narrower type.
auto *Root = dyn_cast<Instruction>(TreeRoot[0]);
if (!Root || !isa<IntegerType>(Root->getType()) || !Root->hasOneUse())
return;
auto Mask = DB->getDemandedBits(Root);
if (Mask.countLeadingZeros() > 0)
MaxBitWidth = Mask.getBitWidth() - Mask.countLeadingZeros();
// If all the bits of the root are demanded, we can try a little harder to
// compute a narrower type. This can happen, for example, if the roots are
// getelementptr indices. InstCombine promotes these indices to the pointer
// width. Thus, all their bits are technically demanded even though the
// address computation might be vectorized in a smaller type. We start by
// looking at each entry in the tree.
else
for (auto &Entry : VectorizableTree) {
// Get a representative value for the vectorizable bundle. All values in
// Entry.Scalars should be isomorphic.
auto *Scalar = Entry.Scalars[0];
// If the scalar is used more than once, InstCombine will not rewrite it,
// so we should give up.
if (!Scalar->hasOneUse())
return;
// We only compute smaller integer types. If the scalar has a different
// type, give up.
auto *IT = dyn_cast<IntegerType>(Scalar->getType());
if (!IT)
return;
// Compute the maximum bit width required to store the scalar. We use
// ValueTracking to compute the number of high-order bits we can
// truncate. We then round up to the next power-of-two.
auto &DL = F->getParent()->getDataLayout();
auto NumSignBits = ComputeNumSignBits(Scalar, DL, 0, AC, 0, DT);
auto NumTypeBits = IT->getBitWidth();
MaxBitWidth = std::max<unsigned>(NumTypeBits - NumSignBits, MaxBitWidth);
}
// Round up to the next power-of-two.
if (!isPowerOf2_64(MaxBitWidth))
MaxBitWidth = NextPowerOf2(MaxBitWidth);
// If the maximum bit width we compute is less than the with of the roots'
// type, we can proceed with the narrowing. Otherwise, do nothing.
auto *RootIT = cast<IntegerType>(TreeRoot[0]->getType());
if (MaxBitWidth > 0 && MaxBitWidth < RootIT->getBitWidth())
MaxRequiredIntegerTy = IntegerType::get(F->getContext(), MaxBitWidth);
}
/// The SLPVectorizer Pass.
struct SLPVectorizer : public FunctionPass {
typedef SmallVector<StoreInst *, 8> StoreList;
@ -3354,7 +3228,6 @@ struct SLPVectorizer : public FunctionPass {
LoopInfo *LI;
DominatorTree *DT;
AssumptionCache *AC;
DemandedBits *DB;
bool runOnFunction(Function &F) override {
if (skipOptnoneFunction(F))
@ -3368,7 +3241,6 @@ struct SLPVectorizer : public FunctionPass {
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
DB = &getAnalysis<DemandedBits>();
Stores.clear();
GEPs.clear();
@ -3398,7 +3270,7 @@ struct SLPVectorizer : public FunctionPass {
// Use the bottom up slp vectorizer to construct chains that start with
// store instructions.
BoUpSLP R(&F, SE, TTI, TLI, AA, LI, DT, AC, DB);
BoUpSLP R(&F, SE, TTI, TLI, AA, LI, DT, AC);
// A general note: the vectorizer must use BoUpSLP::eraseInstruction() to
// delete instructions.
@ -3441,7 +3313,6 @@ struct SLPVectorizer : public FunctionPass {
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.addRequired<LoopInfoWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<DemandedBits>();
AU.addPreserved<LoopInfoWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<AAResultsWrapperPass>();
@ -3546,7 +3417,6 @@ bool SLPVectorizer::vectorizeStoreChain(ArrayRef<Value *> Chain,
ArrayRef<Value *> Operands = Chain.slice(i, VF);
R.buildTree(Operands);
R.computeMaxRequiredIntegerTy();
int Cost = R.getTreeCost();
@ -3746,7 +3616,6 @@ bool SLPVectorizer::tryToVectorizeList(ArrayRef<Value *> VL, BoUpSLP &R,
Value *ReorderedOps[] = { Ops[1], Ops[0] };
R.buildTree(ReorderedOps, None);
}
R.computeMaxRequiredIntegerTy();
int Cost = R.getTreeCost();
if (Cost < -SLPCostThreshold) {
@ -4013,7 +3882,6 @@ public:
for (; i < NumReducedVals - ReduxWidth + 1; i += ReduxWidth) {
V.buildTree(makeArrayRef(&ReducedVals[i], ReduxWidth), ReductionOps);
V.computeMaxRequiredIntegerTy();
// Estimate cost.
int Cost = V.getTreeCost() + getReductionCost(TTI, ReducedVals[i]);

31
test/Transforms/SLPVectorizer/AArch64/gather-reduce.ll
View File

@ -1,5 +1,4 @@
; RUN: opt -S -slp-vectorizer -dce -instcombine < %s | FileCheck %s --check-prefix=PROFITABLE
; RUN: opt -S -slp-vectorizer -slp-threshold=-12 -dce -instcombine < %s | FileCheck %s --check-prefix=UNPROFITABLE
; RUN: opt -S -slp-vectorizer -dce -instcombine < %s | FileCheck %s
target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"
target triple = "aarch64--linux-gnu"
@ -19,13 +18,13 @@ target triple = "aarch64--linux-gnu"
; return sum;
; }
; PROFITABLE-LABEL: @gather_reduce_8x16_i32
; CHECK-LABEL: @gather_reduce_8x16_i32
;
; PROFITABLE: [[L:%[a-zA-Z0-9.]+]] = load <8 x i16>
; PROFITABLE: zext <8 x i16> [[L]] to <8 x i32>
; PROFITABLE: [[S:%[a-zA-Z0-9.]+]] = sub nsw <8 x i32>
; PROFITABLE: [[X:%[a-zA-Z0-9.]+]] = extractelement <8 x i32> [[S]]
; PROFITABLE: sext i32 [[X]] to i64
; CHECK: [[L:%[a-zA-Z0-9.]+]] = load <8 x i16>
; CHECK: zext <8 x i16> [[L]] to <8 x i32>
; CHECK: [[S:%[a-zA-Z0-9.]+]] = sub nsw <8 x i32>
; CHECK: [[X:%[a-zA-Z0-9.]+]] = extractelement <8 x i32> [[S]]
; CHECK: sext i32 [[X]] to i64
;
define i32 @gather_reduce_8x16_i32(i16* nocapture readonly %a, i16* nocapture readonly %b, i16* nocapture readonly %g, i32 %n) {
entry:
@ -138,18 +137,14 @@ for.body:
br i1 %exitcond, label %for.cond.cleanup.loopexit, label %for.body
}
; UNPROFITABLE-LABEL: @gather_reduce_8x16_i64
; CHECK-LABEL: @gather_reduce_8x16_i64
;
; UNPROFITABLE: [[L:%[a-zA-Z0-9.]+]] = load <8 x i16>
; UNPROFITABLE: zext <8 x i16> [[L]] to <8 x i32>
; UNPROFITABLE: [[S:%[a-zA-Z0-9.]+]] = sub nsw <8 x i32>
; UNPROFITABLE: [[X:%[a-zA-Z0-9.]+]] = extractelement <8 x i32> [[S]]
; UNPROFITABLE: sext i32 [[X]] to i64
; CHECK-NOT: load <8 x i16>
;
; TODO: Although we can now vectorize this case while converting the i64
; subtractions to i32, the cost model currently finds vectorization to be
; unprofitable. The cost model is penalizing the sign and zero
; extensions in the vectorized version, but they are actually free.
; FIXME: We are currently unable to vectorize the case with i64 subtraction
; because the zero extensions are too expensive. The solution here is to
; convert the i64 subtractions to i32 subtractions during vectorization.
; This would then match the case above.
;
define i32 @gather_reduce_8x16_i64(i16* nocapture readonly %a, i16* nocapture readonly %b, i16* nocapture readonly %g, i32 %n) {
entry: