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llvm-project/llvm/lib/CodeGen/InterleavedLoadCombinePass.cpp

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//===- InterleavedLoadCombine.cpp - Combine Interleaved Loads ---*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// \file
//
// This file defines the interleaved-load-combine pass. The pass searches for
// ShuffleVectorInstruction that execute interleaving loads. If a matching
// pattern is found, it adds a combined load and further instructions in a
// pattern that is detectable by InterleavedAccesPass. The old instructions are
// left dead to be removed later. The pass is specifically designed to be
// executed just before InterleavedAccesPass to find any left-over instances
// that are not detected within former passes.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/MemorySSA.h"
#include "llvm/Analysis/MemorySSAUpdater.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/TargetLowering.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LegacyPassManager.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include <algorithm>
#include <cassert>
#include <list>
using namespace llvm;
#define DEBUG_TYPE "interleaved-load-combine"
namespace {
/// Statistic counter
STATISTIC(NumInterleavedLoadCombine, "Number of combined loads");
/// Option to disable the pass
static cl::opt<bool> DisableInterleavedLoadCombine(
"disable-" DEBUG_TYPE, cl::init(false), cl::Hidden,
cl::desc("Disable combining of interleaved loads"));
struct VectorInfo;
struct InterleavedLoadCombineImpl {
public:
InterleavedLoadCombineImpl(Function &F, DominatorTree &DT, MemorySSA &MSSA,
TargetMachine &TM)
: F(F), DT(DT), MSSA(MSSA),
TLI(*TM.getSubtargetImpl(F)->getTargetLowering()),
TTI(TM.getTargetTransformInfo(F)) {}
/// Scan the function for interleaved load candidates and execute the
/// replacement if applicable.
bool run();
private:
/// Function this pass is working on
Function &F;
/// Dominator Tree Analysis
DominatorTree &DT;
/// Memory Alias Analyses
MemorySSA &MSSA;
/// Target Lowering Information
const TargetLowering &TLI;
/// Target Transform Information
const TargetTransformInfo TTI;
/// Find the instruction in sets LIs that dominates all others, return nullptr
/// if there is none.
LoadInst *findFirstLoad(const std::set<LoadInst *> &LIs);
/// Replace interleaved load candidates. It does additional
/// analyses if this makes sense. Returns true on success and false
/// of nothing has been changed.
bool combine(std::list<VectorInfo> &InterleavedLoad,
OptimizationRemarkEmitter &ORE);
/// Given a set of VectorInfo containing candidates for a given interleave
/// factor, find a set that represents a 'factor' interleaved load.
bool findPattern(std::list<VectorInfo> &Candidates,
std::list<VectorInfo> &InterleavedLoad, unsigned Factor,
const DataLayout &DL);
}; // InterleavedLoadCombine
/// First Order Polynomial on an n-Bit Integer Value
///
/// Polynomial(Value) = Value * B + A + E*2^(n-e)
///
/// A and B are the coefficients. E*2^(n-e) is an error within 'e' most
/// significant bits. It is introduced if an exact computation cannot be proven
/// (e.q. division by 2).
///
/// As part of this optimization multiple loads will be combined. It necessary
/// to prove that loads are within some relative offset to each other. This
/// class is used to prove relative offsets of values loaded from memory.
///
/// Representing an integer in this form is sound since addition in two's
/// complement is associative (trivial) and multiplication distributes over the
/// addition (see Proof(1) in Polynomial::mul). Further, both operations
/// commute.
//
// Example:
// declare @fn(i64 %IDX, <4 x float>* %PTR) {
// %Pa1 = add i64 %IDX, 2
// %Pa2 = lshr i64 %Pa1, 1
// %Pa3 = getelementptr inbounds <4 x float>, <4 x float>* %PTR, i64 %Pa2
// %Va = load <4 x float>, <4 x float>* %Pa3
//
// %Pb1 = add i64 %IDX, 4
// %Pb2 = lshr i64 %Pb1, 1
// %Pb3 = getelementptr inbounds <4 x float>, <4 x float>* %PTR, i64 %Pb2
// %Vb = load <4 x float>, <4 x float>* %Pb3
// ... }
//
// The goal is to prove that two loads load consecutive addresses.
//
// In this case the polynomials are constructed by the following
// steps.
//
// The number tag #e specifies the error bits.
//
// Pa_0 = %IDX #0
// Pa_1 = %IDX + 2 #0 | add 2
// Pa_2 = %IDX/2 + 1 #1 | lshr 1
// Pa_3 = %IDX/2 + 1 #1 | GEP, step signext to i64
// Pa_4 = (%IDX/2)*16 + 16 #0 | GEP, multiply index by sizeof(4) for floats
// Pa_5 = (%IDX/2)*16 + 16 #0 | GEP, add offset of leading components
//
// Pb_0 = %IDX #0
// Pb_1 = %IDX + 4 #0 | add 2
// Pb_2 = %IDX/2 + 2 #1 | lshr 1
// Pb_3 = %IDX/2 + 2 #1 | GEP, step signext to i64
// Pb_4 = (%IDX/2)*16 + 32 #0 | GEP, multiply index by sizeof(4) for floats
// Pb_5 = (%IDX/2)*16 + 16 #0 | GEP, add offset of leading components
//
// Pb_5 - Pa_5 = 16 #0 | subtract to get the offset
//
// Remark: %PTR is not maintained within this class. So in this instance the
// offset of 16 can only be assumed if the pointers are equal.
//
class Polynomial {
/// Operations on B
enum BOps {
LShr,
Mul,
SExt,
Trunc,
};
/// Number of Error Bits e
unsigned ErrorMSBs;
/// Value
Value *V;
/// Coefficient B
SmallVector<std::pair<BOps, APInt>, 4> B;
/// Coefficient A
APInt A;
public:
Polynomial(Value *V) : ErrorMSBs((unsigned)-1), V(V) {
IntegerType *Ty = dyn_cast<IntegerType>(V->getType());
if (Ty) {
ErrorMSBs = 0;
this->V = V;
A = APInt(Ty->getBitWidth(), 0);
}
}
Polynomial(const APInt &A, unsigned ErrorMSBs = 0)
: ErrorMSBs(ErrorMSBs), V(nullptr), A(A) {}
Polynomial(unsigned BitWidth, uint64_t A, unsigned ErrorMSBs = 0)
: ErrorMSBs(ErrorMSBs), V(nullptr), A(BitWidth, A) {}
Polynomial() : ErrorMSBs((unsigned)-1), V(nullptr) {}
/// Increment and clamp the number of undefined bits.
void incErrorMSBs(unsigned amt) {
if (ErrorMSBs == (unsigned)-1)
return;
ErrorMSBs += amt;
if (ErrorMSBs > A.getBitWidth())
ErrorMSBs = A.getBitWidth();
}
/// Decrement and clamp the number of undefined bits.
void decErrorMSBs(unsigned amt) {
if (ErrorMSBs == (unsigned)-1)
return;
if (ErrorMSBs > amt)
ErrorMSBs -= amt;
else
ErrorMSBs = 0;
}
/// Apply an add on the polynomial
Polynomial &add(const APInt &C) {
// Note: Addition is associative in two's complement even when in case of
// signed overflow.
//
// Error bits can only propagate into higher significant bits. As these are
// already regarded as undefined, there is no change.
//
// Theorem: Adding a constant to a polynomial does not change the error
// term.
//
// Proof:
//
// Since the addition is associative and commutes:
//
// (B + A + E*2^(n-e)) + C = B + (A + C) + E*2^(n-e)
// [qed]
if (C.getBitWidth() != A.getBitWidth()) {
ErrorMSBs = (unsigned)-1;
return *this;
}
A += C;
return *this;
}
/// Apply a multiplication onto the polynomial.
Polynomial &mul(const APInt &C) {
// Note: Multiplication distributes over the addition
//
// Theorem: Multiplication distributes over the addition
//
// Proof(1):
//
// (B+A)*C =-
// = (B + A) + (B + A) + .. {C Times}
// addition is associative and commutes, hence
// = B + B + .. {C Times} .. + A + A + .. {C times}
// = B*C + A*C
// (see (function add) for signed values and overflows)
// [qed]
//
// Theorem: If C has c trailing zeros, errors bits in A or B are shifted out
// to the left.
//
// Proof(2):
//
// Let B' and A' be the n-Bit inputs with some unknown errors EA,
// EB at e leading bits. B' and A' can be written down as:
//
// B' = B + 2^(n-e)*EB
// A' = A + 2^(n-e)*EA
//
// Let C' be an input with c trailing zero bits. C' can be written as
//
// C' = C*2^c
//
// Therefore we can compute the result by using distributivity and
// commutativity.
//
// (B'*C' + A'*C') = [B + 2^(n-e)*EB] * C' + [A + 2^(n-e)*EA] * C' =
// = [B + 2^(n-e)*EB + A + 2^(n-e)*EA] * C' =
// = (B'+A') * C' =
// = [B + 2^(n-e)*EB + A + 2^(n-e)*EA] * C' =
// = [B + A + 2^(n-e)*EB + 2^(n-e)*EA] * C' =
// = (B + A) * C' + [2^(n-e)*EB + 2^(n-e)*EA)] * C' =
// = (B + A) * C' + [2^(n-e)*EB + 2^(n-e)*EA)] * C*2^c =
// = (B + A) * C' + C*(EB + EA)*2^(n-e)*2^c =
//
// Let EC be the final error with EC = C*(EB + EA)
//
// = (B + A)*C' + EC*2^(n-e)*2^c =
// = (B + A)*C' + EC*2^(n-(e-c))
//
// Since EC is multiplied by 2^(n-(e-c)) the resulting error contains c
// less error bits than the input. c bits are shifted out to the left.
// [qed]
if (C.getBitWidth() != A.getBitWidth()) {
ErrorMSBs = (unsigned)-1;
return *this;
}
// Multiplying by one is a no-op.
if (C.isOne()) {
return *this;
}
// Multiplying by zero removes the coefficient B and defines all bits.
if (C.isZero()) {
ErrorMSBs = 0;
deleteB();
}
// See Proof(2): Trailing zero bits indicate a left shift. This removes
// leading bits from the result even if they are undefined.
decErrorMSBs(C.countTrailingZeros());
A *= C;
pushBOperation(Mul, C);
return *this;
}
/// Apply a logical shift right on the polynomial
Polynomial &lshr(const APInt &C) {
// Theorem(1): (B + A + E*2^(n-e)) >> 1 => (B >> 1) + (A >> 1) + E'*2^(n-e')
// where
// e' = e + 1,
// E is a e-bit number,
// E' is a e'-bit number,
// holds under the following precondition:
// pre(1): A % 2 = 0
// pre(2): e < n, (see Theorem(2) for the trivial case with e=n)
// where >> expresses a logical shift to the right, with adding zeros.
//
// We need to show that for every, E there is a E'
//
// B = b_h * 2^(n-1) + b_m * 2 + b_l
// A = a_h * 2^(n-1) + a_m * 2 (pre(1))
//
// where a_h, b_h, b_l are single bits, and a_m, b_m are (n-2) bit numbers
//
// Let X = (B + A + E*2^(n-e)) >> 1
// Let Y = (B >> 1) + (A >> 1) + E*2^(n-e) >> 1
//
// X = [B + A + E*2^(n-e)] >> 1 =
// = [ b_h * 2^(n-1) + b_m * 2 + b_l +
// + a_h * 2^(n-1) + a_m * 2 +
// + E * 2^(n-e) ] >> 1 =
//
// The sum is built by putting the overflow of [a_m + b+n] into the term
// 2^(n-1). As there are no more bits beyond 2^(n-1) the overflow within
// this bit is discarded. This is expressed by % 2.
//
// The bit in position 0 cannot overflow into the term (b_m + a_m).
//
// = [ ([b_h + a_h + (b_m + a_m) >> (n-2)] % 2) * 2^(n-1) +
// + ((b_m + a_m) % 2^(n-2)) * 2 +
// + b_l + E * 2^(n-e) ] >> 1 =
//
// The shift is computed by dividing the terms by 2 and by cutting off
// b_l.
//
// = ([b_h + a_h + (b_m + a_m) >> (n-2)] % 2) * 2^(n-2) +
// + ((b_m + a_m) % 2^(n-2)) +
// + E * 2^(n-(e+1)) =
//
// by the definition in the Theorem e+1 = e'
//
// = ([b_h + a_h + (b_m + a_m) >> (n-2)] % 2) * 2^(n-2) +
// + ((b_m + a_m) % 2^(n-2)) +
// + E * 2^(n-e') =
//
// Compute Y by applying distributivity first
//
// Y = (B >> 1) + (A >> 1) + E*2^(n-e') =
// = (b_h * 2^(n-1) + b_m * 2 + b_l) >> 1 +
// + (a_h * 2^(n-1) + a_m * 2) >> 1 +
// + E * 2^(n-e) >> 1 =
//
// Again, the shift is computed by dividing the terms by 2 and by cutting
// off b_l.
//
// = b_h * 2^(n-2) + b_m +
// + a_h * 2^(n-2) + a_m +
// + E * 2^(n-(e+1)) =
//
// Again, the sum is built by putting the overflow of [a_m + b+n] into
// the term 2^(n-1). But this time there is room for a second bit in the
// term 2^(n-2) we add this bit to a new term and denote it o_h in a
// second step.
//
// = ([b_h + a_h + (b_m + a_m) >> (n-2)] >> 1) * 2^(n-1) +
// + ([b_h + a_h + (b_m + a_m) >> (n-2)] % 2) * 2^(n-2) +
// + ((b_m + a_m) % 2^(n-2)) +
// + E * 2^(n-(e+1)) =
//
// Let o_h = [b_h + a_h + (b_m + a_m) >> (n-2)] >> 1
// Further replace e+1 by e'.
//
// = o_h * 2^(n-1) +
// + ([b_h + a_h + (b_m + a_m) >> (n-2)] % 2) * 2^(n-2) +
// + ((b_m + a_m) % 2^(n-2)) +
// + E * 2^(n-e') =
//
// Move o_h into the error term and construct E'. To ensure that there is
// no 2^x with negative x, this step requires pre(2) (e < n).
//
// = ([b_h + a_h + (b_m + a_m) >> (n-2)] % 2) * 2^(n-2) +
// + ((b_m + a_m) % 2^(n-2)) +
// + o_h * 2^(e'-1) * 2^(n-e') + | pre(2), move 2^(e'-1)
// | out of the old exponent
// + E * 2^(n-e') =
// = ([b_h + a_h + (b_m + a_m) >> (n-2)] % 2) * 2^(n-2) +
// + ((b_m + a_m) % 2^(n-2)) +
// + [o_h * 2^(e'-1) + E] * 2^(n-e') + | move 2^(e'-1) out of
// | the old exponent
//
// Let E' = o_h * 2^(e'-1) + E
//
// = ([b_h + a_h + (b_m + a_m) >> (n-2)] % 2) * 2^(n-2) +
// + ((b_m + a_m) % 2^(n-2)) +
// + E' * 2^(n-e')
//
// Because X and Y are distinct only in there error terms and E' can be
// constructed as shown the theorem holds.
// [qed]
//
// For completeness in case of the case e=n it is also required to show that
// distributivity can be applied.
//
// In this case Theorem(1) transforms to (the pre-condition on A can also be
// dropped)
//
// Theorem(2): (B + A + E) >> 1 => (B >> 1) + (A >> 1) + E'
// where
// A, B, E, E' are two's complement numbers with the same bit
// width
//
// Let A + B + E = X
// Let (B >> 1) + (A >> 1) = Y
//
// Therefore we need to show that for every X and Y there is an E' which
// makes the equation
//
// X = Y + E'
//
// hold. This is trivially the case for E' = X - Y.
//
// [qed]
//
// Remark: Distributing lshr with and arbitrary number n can be expressed as
// ((((B + A) lshr 1) lshr 1) ... ) {n times}.
// This construction induces n additional error bits at the left.
if (C.getBitWidth() != A.getBitWidth()) {
ErrorMSBs = (unsigned)-1;
return *this;
}
if (C.isZero())
return *this;
// Test if the result will be zero
unsigned shiftAmt = C.getZExtValue();
if (shiftAmt >= C.getBitWidth())
return mul(APInt(C.getBitWidth(), 0));
// The proof that shiftAmt LSBs are zero for at least one summand is only
// possible for the constant number.
//
// If this can be proven add shiftAmt to the error counter
// `ErrorMSBs`. Otherwise set all bits as undefined.
if (A.countTrailingZeros() < shiftAmt)
ErrorMSBs = A.getBitWidth();
else
incErrorMSBs(shiftAmt);
// Apply the operation.
pushBOperation(LShr, C);
A = A.lshr(shiftAmt);
return *this;
}
/// Apply a sign-extend or truncate operation on the polynomial.
Polynomial &sextOrTrunc(unsigned n) {
if (n < A.getBitWidth()) {
// Truncate: Clearly undefined Bits on the MSB side are removed
// if there are any.
decErrorMSBs(A.getBitWidth() - n);
A = A.trunc(n);
pushBOperation(Trunc, APInt(sizeof(n) * 8, n));
}
if (n > A.getBitWidth()) {
// Extend: Clearly extending first and adding later is different
// to adding first and extending later in all extended bits.
incErrorMSBs(n - A.getBitWidth());
A = A.sext(n);
pushBOperation(SExt, APInt(sizeof(n) * 8, n));
}
return *this;
}
/// Test if there is a coefficient B.
bool isFirstOrder() const { return V != nullptr; }
/// Test coefficient B of two Polynomials are equal.
bool isCompatibleTo(const Polynomial &o) const {
// The polynomial use different bit width.
if (A.getBitWidth() != o.A.getBitWidth())
return false;
// If neither Polynomial has the Coefficient B.
if (!isFirstOrder() && !o.isFirstOrder())
return true;
// The index variable is different.
if (V != o.V)
return false;
// Check the operations.
if (B.size() != o.B.size())
return false;
auto ob = o.B.begin();
for (auto &b : B) {
if (b != *ob)
return false;
ob++;
}
return true;
}
/// Subtract two polynomials, return an undefined polynomial if
/// subtraction is not possible.
Polynomial operator-(const Polynomial &o) const {
// Return an undefined polynomial if incompatible.
if (!isCompatibleTo(o))
return Polynomial();
// If the polynomials are compatible (meaning they have the same
// coefficient on B), B is eliminated. Thus a polynomial solely
// containing A is returned
return Polynomial(A - o.A, std::max(ErrorMSBs, o.ErrorMSBs));
}
/// Subtract a constant from a polynomial,
Polynomial operator-(uint64_t C) const {
Polynomial Result(*this);
Result.A -= C;
return Result;
}
/// Add a constant to a polynomial,
Polynomial operator+(uint64_t C) const {
Polynomial Result(*this);
Result.A += C;
return Result;
}
/// Returns true if it can be proven that two Polynomials are equal.
bool isProvenEqualTo(const Polynomial &o) {
// Subtract both polynomials and test if it is fully defined and zero.
Polynomial r = *this - o;
return (r.ErrorMSBs == 0) && (!r.isFirstOrder()) && (r.A.isZero());
}
/// Print the polynomial into a stream.
void print(raw_ostream &OS) const {
OS << "[{#ErrBits:" << ErrorMSBs << "} ";
if (V) {
for (auto b : B)
OS << "(";
OS << "(" << *V << ") ";
for (auto b : B) {
switch (b.first) {
case LShr:
OS << "LShr ";
break;
case Mul:
OS << "Mul ";
break;
case SExt:
OS << "SExt ";
break;
case Trunc:
OS << "Trunc ";
break;
}
OS << b.second << ") ";
}
}
OS << "+ " << A << "]";
}
private:
void deleteB() {
V = nullptr;
B.clear();
}
void pushBOperation(const BOps Op, const APInt &C) {
if (isFirstOrder()) {
B.push_back(std::make_pair(Op, C));
return;
}
}
};
#ifndef NDEBUG
static raw_ostream &operator<<(raw_ostream &OS, const Polynomial &S) {
S.print(OS);
return OS;
}
#endif
/// VectorInfo stores abstract the following information for each vector
/// element:
///
/// 1) The the memory address loaded into the element as Polynomial
/// 2) a set of load instruction necessary to construct the vector,
/// 3) a set of all other instructions that are necessary to create the vector and
/// 4) a pointer value that can be used as relative base for all elements.
struct VectorInfo {
private:
VectorInfo(const VectorInfo &c) : VTy(c.VTy) {
llvm_unreachable(
"Copying VectorInfo is neither implemented nor necessary,");
}
public:
/// Information of a Vector Element
struct ElementInfo {
/// Offset Polynomial.
Polynomial Ofs;
/// The Load Instruction used to Load the entry. LI is null if the pointer
/// of the load instruction does not point on to the entry
LoadInst *LI;
ElementInfo(Polynomial Offset = Polynomial(), LoadInst *LI = nullptr)
: Ofs(Offset), LI(LI) {}
};
/// Basic-block the load instructions are within
BasicBlock *BB;
/// Pointer value of all participation load instructions
Value *PV;
/// Participating load instructions
std::set<LoadInst *> LIs;
/// Participating instructions
std::set<Instruction *> Is;
/// Final shuffle-vector instruction
ShuffleVectorInst *SVI;
/// Information of the offset for each vector element
ElementInfo *EI;
/// Vector Type
FixedVectorType *const VTy;
VectorInfo(FixedVectorType *VTy)
: BB(nullptr), PV(nullptr), SVI(nullptr), VTy(VTy) {
EI = new ElementInfo[VTy->getNumElements()];
}
virtual ~VectorInfo() { delete[] EI; }
unsigned getDimension() const { return VTy->getNumElements(); }
/// Test if the VectorInfo can be part of an interleaved load with the
/// specified factor.
///
/// \param Factor of the interleave
/// \param DL Targets Datalayout
///
/// \returns true if this is possible and false if not
bool isInterleaved(unsigned Factor, const DataLayout &DL) const {
unsigned Size = DL.getTypeAllocSize(VTy->getElementType());
for (unsigned i = 1; i < getDimension(); i++) {
if (!EI[i].Ofs.isProvenEqualTo(EI[0].Ofs + i * Factor * Size)) {
return false;
}
}
return true;
}
/// Recursively computes the vector information stored in V.
///
/// This function delegates the work to specialized implementations
///
/// \param V Value to operate on
/// \param Result Result of the computation
///
/// \returns false if no sensible information can be gathered.
static bool compute(Value *V, VectorInfo &Result, const DataLayout &DL) {
ShuffleVectorInst *SVI = dyn_cast<ShuffleVectorInst>(V);
if (SVI)
return computeFromSVI(SVI, Result, DL);
LoadInst *LI = dyn_cast<LoadInst>(V);
if (LI)
return computeFromLI(LI, Result, DL);
BitCastInst *BCI = dyn_cast<BitCastInst>(V);
if (BCI)
return computeFromBCI(BCI, Result, DL);
return false;
}
/// BitCastInst specialization to compute the vector information.
///
/// \param BCI BitCastInst to operate on
/// \param Result Result of the computation
///
/// \returns false if no sensible information can be gathered.
static bool computeFromBCI(BitCastInst *BCI, VectorInfo &Result,
const DataLayout &DL) {
Instruction *Op = dyn_cast<Instruction>(BCI->getOperand(0));
if (!Op)
return false;
FixedVectorType *VTy = dyn_cast<FixedVectorType>(Op->getType());
if (!VTy)
return false;
// We can only cast from large to smaller vectors
if (Result.VTy->getNumElements() % VTy->getNumElements())
return false;
unsigned Factor = Result.VTy->getNumElements() / VTy->getNumElements();
unsigned NewSize = DL.getTypeAllocSize(Result.VTy->getElementType());
unsigned OldSize = DL.getTypeAllocSize(VTy->getElementType());
if (NewSize * Factor != OldSize)
return false;
VectorInfo Old(VTy);
if (!compute(Op, Old, DL))
return false;
for (unsigned i = 0; i < Result.VTy->getNumElements(); i += Factor) {
for (unsigned j = 0; j < Factor; j++) {
Result.EI[i + j] =
ElementInfo(Old.EI[i / Factor].Ofs + j * NewSize,
j == 0 ? Old.EI[i / Factor].LI : nullptr);
}
}
Result.BB = Old.BB;
Result.PV = Old.PV;
Result.LIs.insert(Old.LIs.begin(), Old.LIs.end());
Result.Is.insert(Old.Is.begin(), Old.Is.end());
Result.Is.insert(BCI);
Result.SVI = nullptr;
return true;
}
/// ShuffleVectorInst specialization to compute vector information.
///
/// \param SVI ShuffleVectorInst to operate on
/// \param Result Result of the computation
///
/// Compute the left and the right side vector information and merge them by
/// applying the shuffle operation. This function also ensures that the left
/// and right side have compatible loads. This means that all loads are with
/// in the same basic block and are based on the same pointer.
///
/// \returns false if no sensible information can be gathered.
static bool computeFromSVI(ShuffleVectorInst *SVI, VectorInfo &Result,
const DataLayout &DL) {
FixedVectorType *ArgTy =
cast<FixedVectorType>(SVI->getOperand(0)->getType());
// Compute the left hand vector information.
VectorInfo LHS(ArgTy);
if (!compute(SVI->getOperand(0), LHS, DL))
LHS.BB = nullptr;
// Compute the right hand vector information.
VectorInfo RHS(ArgTy);
if (!compute(SVI->getOperand(1), RHS, DL))
RHS.BB = nullptr;
// Neither operand produced sensible results?
if (!LHS.BB && !RHS.BB)
return false;
// Only RHS produced sensible results?
else if (!LHS.BB) {
Result.BB = RHS.BB;
Result.PV = RHS.PV;
}
// Only LHS produced sensible results?
else if (!RHS.BB) {
Result.BB = LHS.BB;
Result.PV = LHS.PV;
}
// Both operands produced sensible results?
else if ((LHS.BB == RHS.BB) && (LHS.PV == RHS.PV)) {
Result.BB = LHS.BB;
Result.PV = LHS.PV;
}
// Both operands produced sensible results but they are incompatible.
else {
return false;
}
// Merge and apply the operation on the offset information.
if (LHS.BB) {
Result.LIs.insert(LHS.LIs.begin(), LHS.LIs.end());
Result.Is.insert(LHS.Is.begin(), LHS.Is.end());
}
if (RHS.BB) {
Result.LIs.insert(RHS.LIs.begin(), RHS.LIs.end());
Result.Is.insert(RHS.Is.begin(), RHS.Is.end());
}
Result.Is.insert(SVI);
Result.SVI = SVI;
int j = 0;
for (int i : SVI->getShuffleMask()) {
assert((i < 2 * (signed)ArgTy->getNumElements()) &&
"Invalid ShuffleVectorInst (index out of bounds)");
if (i < 0)
Result.EI[j] = ElementInfo();
else if (i < (signed)ArgTy->getNumElements()) {
if (LHS.BB)
Result.EI[j] = LHS.EI[i];
else
Result.EI[j] = ElementInfo();
} else {
if (RHS.BB)
Result.EI[j] = RHS.EI[i - ArgTy->getNumElements()];
else
Result.EI[j] = ElementInfo();
}
j++;
}
return true;
}
/// LoadInst specialization to compute vector information.
///
/// This function also acts as abort condition to the recursion.
///
/// \param LI LoadInst to operate on
/// \param Result Result of the computation
///
/// \returns false if no sensible information can be gathered.
static bool computeFromLI(LoadInst *LI, VectorInfo &Result,
const DataLayout &DL) {
Value *BasePtr;
Polynomial Offset;
if (LI->isVolatile())
return false;
if (LI->isAtomic())
return false;
// Get the base polynomial
computePolynomialFromPointer(*LI->getPointerOperand(), Offset, BasePtr, DL);
Result.BB = LI->getParent();
Result.PV = BasePtr;
Result.LIs.insert(LI);
Result.Is.insert(LI);
for (unsigned i = 0; i < Result.getDimension(); i++) {
Value *Idx[2] = {
ConstantInt::get(Type::getInt32Ty(LI->getContext()), 0),
ConstantInt::get(Type::getInt32Ty(LI->getContext()), i),
};
int64_t Ofs = DL.getIndexedOffsetInType(Result.VTy, makeArrayRef(Idx, 2));
Result.EI[i] = ElementInfo(Offset + Ofs, i == 0 ? LI : nullptr);
}
return true;
}
/// Recursively compute polynomial of a value.
///
/// \param BO Input binary operation
/// \param Result Result polynomial
static void computePolynomialBinOp(BinaryOperator &BO, Polynomial &Result) {
Value *LHS = BO.getOperand(0);
Value *RHS = BO.getOperand(1);
// Find the RHS Constant if any
ConstantInt *C = dyn_cast<ConstantInt>(RHS);
if ((!C) && BO.isCommutative()) {
C = dyn_cast<ConstantInt>(LHS);
if (C)
std::swap(LHS, RHS);
}
switch (BO.getOpcode()) {
case Instruction::Add:
if (!C)
break;
computePolynomial(*LHS, Result);
Result.add(C->getValue());
return;
case Instruction::LShr:
if (!C)
break;
computePolynomial(*LHS, Result);
Result.lshr(C->getValue());
return;
default:
break;
}
Result = Polynomial(&BO);
}
/// Recursively compute polynomial of a value
///
/// \param V input value
/// \param Result result polynomial
static void computePolynomial(Value &V, Polynomial &Result) {
if (auto *BO = dyn_cast<BinaryOperator>(&V))
computePolynomialBinOp(*BO, Result);
else
Result = Polynomial(&V);
}
/// Compute the Polynomial representation of a Pointer type.
///
/// \param Ptr input pointer value
/// \param Result result polynomial
/// \param BasePtr pointer the polynomial is based on
/// \param DL Datalayout of the target machine
static void computePolynomialFromPointer(Value &Ptr, Polynomial &Result,
Value *&BasePtr,
const DataLayout &DL) {
// Not a pointer type? Return an undefined polynomial
PointerType *PtrTy = dyn_cast<PointerType>(Ptr.getType());
if (!PtrTy) {
Result = Polynomial();
BasePtr = nullptr;
return;
}
unsigned PointerBits =
DL.getIndexSizeInBits(PtrTy->getPointerAddressSpace());
/// Skip pointer casts. Return Zero polynomial otherwise
if (isa<CastInst>(&Ptr)) {
CastInst &CI = *cast<CastInst>(&Ptr);
switch (CI.getOpcode()) {
case Instruction::BitCast:
computePolynomialFromPointer(*CI.getOperand(0), Result, BasePtr, DL);
break;
default:
BasePtr = &Ptr;
Polynomial(PointerBits, 0);
break;
}
}
/// Resolve GetElementPtrInst.
else if (isa<GetElementPtrInst>(&Ptr)) {
GetElementPtrInst &GEP = *cast<GetElementPtrInst>(&Ptr);
APInt BaseOffset(PointerBits, 0);
// Check if we can compute the Offset with accumulateConstantOffset
if (GEP.accumulateConstantOffset(DL, BaseOffset)) {
Result = Polynomial(BaseOffset);
BasePtr = GEP.getPointerOperand();
return;
} else {
// Otherwise we allow that the last index operand of the GEP is
// non-constant.
unsigned idxOperand, e;
SmallVector<Value *, 4> Indices;
for (idxOperand = 1, e = GEP.getNumOperands(); idxOperand < e;
idxOperand++) {
ConstantInt *IDX = dyn_cast<ConstantInt>(GEP.getOperand(idxOperand));
if (!IDX)
break;
Indices.push_back(IDX);
}
// It must also be the last operand.
if (idxOperand + 1 != e) {
Result = Polynomial();
BasePtr = nullptr;
return;
}
// Compute the polynomial of the index operand.
computePolynomial(*GEP.getOperand(idxOperand), Result);
// Compute base offset from zero based index, excluding the last
// variable operand.
BaseOffset =
DL.getIndexedOffsetInType(GEP.getSourceElementType(), Indices);
// Apply the operations of GEP to the polynomial.
unsigned ResultSize = DL.getTypeAllocSize(GEP.getResultElementType());
Result.sextOrTrunc(PointerBits);
Result.mul(APInt(PointerBits, ResultSize));
Result.add(BaseOffset);
BasePtr = GEP.getPointerOperand();
}
}
// All other instructions are handled by using the value as base pointer and
// a zero polynomial.
else {
BasePtr = &Ptr;
Polynomial(DL.getIndexSizeInBits(PtrTy->getPointerAddressSpace()), 0);
}
}
#ifndef NDEBUG
void print(raw_ostream &OS) const {
if (PV)
OS << *PV;
else
OS << "(none)";
OS << " + ";
for (unsigned i = 0; i < getDimension(); i++)
OS << ((i == 0) ? "[" : ", ") << EI[i].Ofs;
OS << "]";
}
#endif
};
} // anonymous namespace
bool InterleavedLoadCombineImpl::findPattern(
std::list<VectorInfo> &Candidates, std::list<VectorInfo> &InterleavedLoad,
unsigned Factor, const DataLayout &DL) {
for (auto C0 = Candidates.begin(), E0 = Candidates.end(); C0 != E0; ++C0) {
unsigned i;
// Try to find an interleaved load using the front of Worklist as first line
unsigned Size = DL.getTypeAllocSize(C0->VTy->getElementType());
// List containing iterators pointing to the VectorInfos of the candidates
std::vector<std::list<VectorInfo>::iterator> Res(Factor, Candidates.end());
for (auto C = Candidates.begin(), E = Candidates.end(); C != E; C++) {
if (C->VTy != C0->VTy)
continue;
if (C->BB != C0->BB)
continue;
if (C->PV != C0->PV)
continue;
// Check the current value matches any of factor - 1 remaining lines
for (i = 1; i < Factor; i++) {
if (C->EI[0].Ofs.isProvenEqualTo(C0->EI[0].Ofs + i * Size)) {
Res[i] = C;
}
}
for (i = 1; i < Factor; i++) {
if (Res[i] == Candidates.end())
break;
}
if (i == Factor) {
Res[0] = C0;
break;
}
}
if (Res[0] != Candidates.end()) {
// Move the result into the output
for (unsigned i = 0; i < Factor; i++) {
InterleavedLoad.splice(InterleavedLoad.end(), Candidates, Res[i]);
}
return true;
}
}
return false;
}
LoadInst *
InterleavedLoadCombineImpl::findFirstLoad(const std::set<LoadInst *> &LIs) {
assert(!LIs.empty() && "No load instructions given.");
// All LIs are within the same BB. Select the first for a reference.
BasicBlock *BB = (*LIs.begin())->getParent();
BasicBlock::iterator FLI = llvm::find_if(
*BB, [&LIs](Instruction &I) -> bool { return is_contained(LIs, &I); });
assert(FLI != BB->end());
return cast<LoadInst>(FLI);
}
bool InterleavedLoadCombineImpl::combine(std::list<VectorInfo> &InterleavedLoad,
OptimizationRemarkEmitter &ORE) {
LLVM_DEBUG(dbgs() << "Checking interleaved load\n");
// The insertion point is the LoadInst which loads the first values. The
// following tests are used to proof that the combined load can be inserted
// just before InsertionPoint.
LoadInst *InsertionPoint = InterleavedLoad.front().EI[0].LI;
// Test if the offset is computed
if (!InsertionPoint)
return false;
std::set<LoadInst *> LIs;
std::set<Instruction *> Is;
std::set<Instruction *> SVIs;
InstructionCost InterleavedCost;
InstructionCost InstructionCost = 0;
const TTI::TargetCostKind CostKind = TTI::TCK_SizeAndLatency;
// Get the interleave factor
unsigned Factor = InterleavedLoad.size();
// Merge all input sets used in analysis
for (auto &VI : InterleavedLoad) {
// Generate a set of all load instructions to be combined
LIs.insert(VI.LIs.begin(), VI.LIs.end());
// Generate a set of all instructions taking part in load
// interleaved. This list excludes the instructions necessary for the
// polynomial construction.
Is.insert(VI.Is.begin(), VI.Is.end());
// Generate the set of the final ShuffleVectorInst.
SVIs.insert(VI.SVI);
}
// There is nothing to combine.
if (LIs.size() < 2)
return false;
// Test if all participating instruction will be dead after the
// transformation. If intermediate results are used, no performance gain can
// be expected. Also sum the cost of the Instructions beeing left dead.
for (auto &I : Is) {
// Compute the old cost
InstructionCost += TTI.getInstructionCost(I, CostKind);
// The final SVIs are allowed not to be dead, all uses will be replaced
if (SVIs.find(I) != SVIs.end())
continue;
// If there are users outside the set to be eliminated, we abort the
// transformation. No gain can be expected.
for (auto *U : I->users()) {
if (Is.find(dyn_cast<Instruction>(U)) == Is.end())
return false;
}
}
// We need to have a valid cost in order to proceed.
if (!InstructionCost.isValid())
return false;
// We know that all LoadInst are within the same BB. This guarantees that
// either everything or nothing is loaded.
LoadInst *First = findFirstLoad(LIs);
// To be safe that the loads can be combined, iterate over all loads and test
// that the corresponding defining access dominates first LI. This guarantees
// that there are no aliasing stores in between the loads.
auto FMA = MSSA.getMemoryAccess(First);
for (auto LI : LIs) {
auto MADef = MSSA.getMemoryAccess(LI)->getDefiningAccess();
if (!MSSA.dominates(MADef, FMA))
return false;
}
assert(!LIs.empty() && "There are no LoadInst to combine");
// It is necessary that insertion point dominates all final ShuffleVectorInst.
for (auto &VI : InterleavedLoad) {
if (!DT.dominates(InsertionPoint, VI.SVI))
return false;
}
// All checks are done. Add instructions detectable by InterleavedAccessPass
// The old instruction will are left dead.
IRBuilder<> Builder(InsertionPoint);
Type *ETy = InterleavedLoad.front().SVI->getType()->getElementType();
unsigned ElementsPerSVI =
cast<FixedVectorType>(InterleavedLoad.front().SVI->getType())
->getNumElements();
FixedVectorType *ILTy = FixedVectorType::get(ETy, Factor * ElementsPerSVI);
SmallVector<unsigned, 4> Indices;
for (unsigned i = 0; i < Factor; i++)
Indices.push_back(i);
InterleavedCost = TTI.getInterleavedMemoryOpCost(
Instruction::Load, ILTy, Factor, Indices, InsertionPoint->getAlign(),
InsertionPoint->getPointerAddressSpace(), CostKind);
if (InterleavedCost >= InstructionCost) {
return false;
}
// Create a pointer cast for the wide load.
auto CI = Builder.CreatePointerCast(InsertionPoint->getOperand(0),
ILTy->getPointerTo(),
"interleaved.wide.ptrcast");
// Create the wide load and update the MemorySSA.
auto LI = Builder.CreateAlignedLoad(ILTy, CI, InsertionPoint->getAlign(),
"interleaved.wide.load");
auto MSSAU = MemorySSAUpdater(&MSSA);
MemoryUse *MSSALoad = cast<MemoryUse>(MSSAU.createMemoryAccessBefore(
LI, nullptr, MSSA.getMemoryAccess(InsertionPoint)));
MSSAU.insertUse(MSSALoad);
// Create the final SVIs and replace all uses.
int i = 0;
for (auto &VI : InterleavedLoad) {
SmallVector<int, 4> Mask;
for (unsigned j = 0; j < ElementsPerSVI; j++)
Mask.push_back(i + j * Factor);
Builder.SetInsertPoint(VI.SVI);
auto SVI = Builder.CreateShuffleVector(LI, Mask, "interleaved.shuffle");
VI.SVI->replaceAllUsesWith(SVI);
i++;
}
NumInterleavedLoadCombine++;
ORE.emit([&]() {
return OptimizationRemark(DEBUG_TYPE, "Combined Interleaved Load", LI)
<< "Load interleaved combined with factor "
<< ore::NV("Factor", Factor);
});
return true;
}
bool InterleavedLoadCombineImpl::run() {
OptimizationRemarkEmitter ORE(&F);
bool changed = false;
unsigned MaxFactor = TLI.getMaxSupportedInterleaveFactor();
auto &DL = F.getParent()->getDataLayout();
// Start with the highest factor to avoid combining and recombining.
for (unsigned Factor = MaxFactor; Factor >= 2; Factor--) {
std::list<VectorInfo> Candidates;
for (BasicBlock &BB : F) {
for (Instruction &I : BB) {
if (auto SVI = dyn_cast<ShuffleVectorInst>(&I)) {
// We don't support scalable vectors in this pass.
if (isa<ScalableVectorType>(SVI->getType()))
continue;
Candidates.emplace_back(cast<FixedVectorType>(SVI->getType()));
if (!VectorInfo::computeFromSVI(SVI, Candidates.back(), DL)) {
Candidates.pop_back();
continue;
}
if (!Candidates.back().isInterleaved(Factor, DL)) {
Candidates.pop_back();
}
}
}
}
std::list<VectorInfo> InterleavedLoad;
while (findPattern(Candidates, InterleavedLoad, Factor, DL)) {
if (combine(InterleavedLoad, ORE)) {
changed = true;
} else {
// Remove the first element of the Interleaved Load but put the others
// back on the list and continue searching
Candidates.splice(Candidates.begin(), InterleavedLoad,
std::next(InterleavedLoad.begin()),
InterleavedLoad.end());
}
InterleavedLoad.clear();
}
}
return changed;
}
namespace {
/// This pass combines interleaved loads into a pattern detectable by
/// InterleavedAccessPass.
struct InterleavedLoadCombine : public FunctionPass {
static char ID;
InterleavedLoadCombine() : FunctionPass(ID) {
initializeInterleavedLoadCombinePass(*PassRegistry::getPassRegistry());
}
StringRef getPassName() const override {
return "Interleaved Load Combine Pass";
}
bool runOnFunction(Function &F) override {
if (DisableInterleavedLoadCombine)
return false;
auto *TPC = getAnalysisIfAvailable<TargetPassConfig>();
if (!TPC)
return false;
LLVM_DEBUG(dbgs() << "*** " << getPassName() << ": " << F.getName()
<< "\n");
return InterleavedLoadCombineImpl(
F, getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
getAnalysis<MemorySSAWrapperPass>().getMSSA(),
TPC->getTM<TargetMachine>())
.run();
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MemorySSAWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
FunctionPass::getAnalysisUsage(AU);
}
private:
};
} // anonymous namespace
char InterleavedLoadCombine::ID = 0;
INITIALIZE_PASS_BEGIN(
InterleavedLoadCombine, DEBUG_TYPE,
"Combine interleaved loads into wide loads and shufflevector instructions",
false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
INITIALIZE_PASS_END(
InterleavedLoadCombine, DEBUG_TYPE,
"Combine interleaved loads into wide loads and shufflevector instructions",
false, false)
FunctionPass *
llvm::createInterleavedLoadCombinePass() {
auto P = new InterleavedLoadCombine();
return P;
}
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