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llvm/lib/CodeGen/InterleavedLoadCombinePass.cpp
Chandler Carruth 6b547686c5 Update the file headers across all of the LLVM projects in the monorepo 
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351636 91177308-0d34-0410-b5e6-96231b3b80d8
2019-01-19 08:50:56 +00:00

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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/LegacyPassManager.h"
#include "llvm/IR/Module.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), B(), A() {
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(NULL), B(), A(A) {}
Polynomial(unsigned BitWidth, uint64_t A, unsigned ErrorMSBs = 0)
: ErrorMSBs(ErrorMSBs), V(NULL), B(), A(BitWidth, A) {}
Polynomial() : ErrorMSBs((unsigned)-1), V(NULL), B(), A() {}
/// 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.isOneValue()) {
return *this;
}
// Multiplying by zero removes the coefficient B and defines all bits.
if (C.isNullValue()) {
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.isNullValue())
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.isNullValue());
}
/// 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
VectorType *const VTy;
VectorInfo(VectorType *VTy)
: BB(nullptr), PV(nullptr), LIs(), Is(), 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;
VectorType *VTy = dyn_cast<VectorType>(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) {
VectorType *ArgTy = dyn_cast<VectorType>(SVI->getOperand(0)->getType());
assert(ArgTy && "ShuffleVector Operand is not a VectorType");
// 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 (isa<BinaryOperator>(&V))
computePolynomialBinOp(*dyn_cast<BinaryOperator>(&V), 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;
}
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 =
std::find_if(BB->begin(), BB->end(), [&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;
unsigned InterleavedCost;
unsigned InstructionCost = 0;
// 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, TargetTransformInfo::TCK_Latency);
// 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 (const auto &U : I->users()) {
if (Is.find(dyn_cast<Instruction>(U)) == Is.end())
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 =
InterleavedLoad.front().SVI->getType()->getNumElements();
VectorType *ILTy = VectorType::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->getAlignment(),
InsertionPoint->getPointerAddressSpace());
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(CI, InsertionPoint->getAlignment(),
"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<uint32_t, 4> Mask;
for (unsigned j = 0; j < ElementsPerSVI; j++)
Mask.push_back(i + j * Factor);
Builder.SetInsertPoint(VI.SVI);
auto SVI = Builder.CreateShuffleVector(LI, UndefValue::get(LI->getType()),
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)) {
Candidates.emplace_back(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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