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llvm/lib/Target/PowerPC/PPCVSXSwapRemoval.cpp
Kit Barton d1168ef803 Ensure all uses of permute instructions feed vector stores 
There is a problem in VSXSwapRemoval where it is incorrectly removing permute instructions.
In this case, the permute is feeding both a vector store and also a non-store instruction. In this case, the permute cannot be removed.

The fix is to simply look at all the uses of the vector register defined by the permute and ensure that all the uses are vector store instructions.

This problem was reported in PR 27735 (https://llvm.org/bugs/show_bug.cgi?id=27735).

Test case based on the original problem reported.

Phabricator Review: http://reviews.llvm.org/D21802

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274645 91177308-0d34-0410-b5e6-96231b3b80d8
2016-07-06 18:03:52 +00:00

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//===----------- PPCVSXSwapRemoval.cpp - Remove VSX LE Swaps -------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===---------------------------------------------------------------------===//
//
// This pass analyzes vector computations and removes unnecessary
// doubleword swaps (xxswapd instructions). This pass is performed
// only for little-endian VSX code generation.
//
// For this specific case, loads and stores of v4i32, v4f32, v2i64,
// and v2f64 vectors are inefficient. These are implemented using
// the lxvd2x and stxvd2x instructions, which invert the order of
// doublewords in a vector register. Thus code generation inserts
// an xxswapd after each such load, and prior to each such store.
//
// The extra xxswapd instructions reduce performance. The purpose
// of this pass is to reduce the number of xxswapd instructions
// required for correctness.
//
// The primary insight is that much code that operates on vectors
// does not care about the relative order of elements in a register,
// so long as the correct memory order is preserved. If we have a
// computation where all input values are provided by lxvd2x/xxswapd,
// all outputs are stored using xxswapd/lxvd2x, and all intermediate
// computations are lane-insensitive (independent of element order),
// then all the xxswapd instructions associated with the loads and
// stores may be removed without changing observable semantics.
//
// This pass uses standard equivalence class infrastructure to create
// maximal webs of computations fitting the above description. Each
// such web is then optimized by removing its unnecessary xxswapd
// instructions.
//
// There are some lane-sensitive operations for which we can still
// permit the optimization, provided we modify those operations
// accordingly. Such operations are identified as using "special
// handling" within this module.
//
//===---------------------------------------------------------------------===//
#include "PPCInstrInfo.h"
#include "PPC.h"
#include "PPCInstrBuilder.h"
#include "PPCTargetMachine.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/EquivalenceClasses.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "ppc-vsx-swaps"
namespace llvm {
void initializePPCVSXSwapRemovalPass(PassRegistry&);
}
namespace {
// A PPCVSXSwapEntry is created for each machine instruction that
// is relevant to a vector computation.
struct PPCVSXSwapEntry {
// Pointer to the instruction.
MachineInstr *VSEMI;
// Unique ID (position in the swap vector).
int VSEId;
// Attributes of this node.
unsigned int IsLoad : 1;
unsigned int IsStore : 1;
unsigned int IsSwap : 1;
unsigned int MentionsPhysVR : 1;
unsigned int IsSwappable : 1;
unsigned int MentionsPartialVR : 1;
unsigned int SpecialHandling : 3;
unsigned int WebRejected : 1;
unsigned int WillRemove : 1;
};
enum SHValues {
SH_NONE = 0,
SH_EXTRACT,
SH_INSERT,
SH_NOSWAP_LD,
SH_NOSWAP_ST,
SH_SPLAT,
SH_XXPERMDI,
SH_COPYWIDEN
};
struct PPCVSXSwapRemoval : public MachineFunctionPass {
static char ID;
const PPCInstrInfo *TII;
MachineFunction *MF;
MachineRegisterInfo *MRI;
// Swap entries are allocated in a vector for better performance.
std::vector<PPCVSXSwapEntry> SwapVector;
// A mapping is maintained between machine instructions and
// their swap entries. The key is the address of the MI.
DenseMap<MachineInstr*, int> SwapMap;
// Equivalence classes are used to gather webs of related computation.
// Swap entries are represented by their VSEId fields.
EquivalenceClasses<int> *EC;
PPCVSXSwapRemoval() : MachineFunctionPass(ID) {
initializePPCVSXSwapRemovalPass(*PassRegistry::getPassRegistry());
}
private:
// Initialize data structures.
void initialize(MachineFunction &MFParm);
// Walk the machine instructions to gather vector usage information.
// Return true iff vector mentions are present.
bool gatherVectorInstructions();
// Add an entry to the swap vector and swap map.
int addSwapEntry(MachineInstr *MI, PPCVSXSwapEntry &SwapEntry);
// Hunt backwards through COPY and SUBREG_TO_REG chains for a
// source register. VecIdx indicates the swap vector entry to
// mark as mentioning a physical register if the search leads
// to one.
unsigned lookThruCopyLike(unsigned SrcReg, unsigned VecIdx);
// Generate equivalence classes for related computations (webs).
void formWebs();
// Analyze webs and determine those that cannot be optimized.
void recordUnoptimizableWebs();
// Record which swap instructions can be safely removed.
void markSwapsForRemoval();
// Remove swaps and update other instructions requiring special
// handling. Return true iff any changes are made.
bool removeSwaps();
// Insert a swap instruction from SrcReg to DstReg at the given
// InsertPoint.
void insertSwap(MachineInstr *MI, MachineBasicBlock::iterator InsertPoint,
unsigned DstReg, unsigned SrcReg);
// Update instructions requiring special handling.
void handleSpecialSwappables(int EntryIdx);
// Dump a description of the entries in the swap vector.
void dumpSwapVector();
// Return true iff the given register is in the given class.
bool isRegInClass(unsigned Reg, const TargetRegisterClass *RC) {
if (TargetRegisterInfo::isVirtualRegister(Reg))
return RC->hasSubClassEq(MRI->getRegClass(Reg));
return RC->contains(Reg);
}
// Return true iff the given register is a full vector register.
bool isVecReg(unsigned Reg) {
return (isRegInClass(Reg, &PPC::VSRCRegClass) ||
isRegInClass(Reg, &PPC::VRRCRegClass));
}
// Return true iff the given register is a partial vector register.
bool isScalarVecReg(unsigned Reg) {
return (isRegInClass(Reg, &PPC::VSFRCRegClass) ||
isRegInClass(Reg, &PPC::VSSRCRegClass));
}
// Return true iff the given register mentions all or part of a
// vector register. Also sets Partial to true if the mention
// is for just the floating-point register overlap of the register.
bool isAnyVecReg(unsigned Reg, bool &Partial) {
if (isScalarVecReg(Reg))
Partial = true;
return isScalarVecReg(Reg) || isVecReg(Reg);
}
public:
// Main entry point for this pass.
bool runOnMachineFunction(MachineFunction &MF) override {
if (skipFunction(*MF.getFunction()))
return false;
// If we don't have VSX on the subtarget, don't do anything.
const PPCSubtarget &STI = MF.getSubtarget<PPCSubtarget>();
if (!STI.hasVSX())
return false;
bool Changed = false;
initialize(MF);
if (gatherVectorInstructions()) {
formWebs();
recordUnoptimizableWebs();
markSwapsForRemoval();
Changed = removeSwaps();
}
// FIXME: See the allocation of EC in initialize().
delete EC;
return Changed;
}
};
// Initialize data structures for this pass. In particular, clear the
// swap vector and allocate the equivalence class mapping before
// processing each function.
void PPCVSXSwapRemoval::initialize(MachineFunction &MFParm) {
MF = &MFParm;
MRI = &MF->getRegInfo();
TII = MF->getSubtarget<PPCSubtarget>().getInstrInfo();
// An initial vector size of 256 appears to work well in practice.
// Small/medium functions with vector content tend not to incur a
// reallocation at this size. Three of the vector tests in
// projects/test-suite reallocate, which seems like a reasonable rate.
const int InitialVectorSize(256);
SwapVector.clear();
SwapVector.reserve(InitialVectorSize);
// FIXME: Currently we allocate EC each time because we don't have
// access to the set representation on which to call clear(). Should
// consider adding a clear() method to the EquivalenceClasses class.
EC = new EquivalenceClasses<int>;
}
// Create an entry in the swap vector for each instruction that mentions
// a full vector register, recording various characteristics of the
// instructions there.
bool PPCVSXSwapRemoval::gatherVectorInstructions() {
bool RelevantFunction = false;
for (MachineBasicBlock &MBB : *MF) {
for (MachineInstr &MI : MBB) {
if (MI.isDebugValue())
continue;
bool RelevantInstr = false;
bool Partial = false;
for (const MachineOperand &MO : MI.operands()) {
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (isAnyVecReg(Reg, Partial)) {
RelevantInstr = true;
break;
}
}
if (!RelevantInstr)
continue;
RelevantFunction = true;
// Create a SwapEntry initialized to zeros, then fill in the
// instruction and ID fields before pushing it to the back
// of the swap vector.
PPCVSXSwapEntry SwapEntry{};
int VecIdx = addSwapEntry(&MI, SwapEntry);
switch(MI.getOpcode()) {
default:
// Unless noted otherwise, an instruction is considered
// safe for the optimization. There are a large number of
// such true-SIMD instructions (all vector math, logical,
// select, compare, etc.). However, if the instruction
// mentions a partial vector register and does not have
// special handling defined, it is not swappable.
if (Partial)
SwapVector[VecIdx].MentionsPartialVR = 1;
else
SwapVector[VecIdx].IsSwappable = 1;
break;
case PPC::XXPERMDI: {
// This is a swap if it is of the form XXPERMDI t, s, s, 2.
// Unfortunately, MachineCSE ignores COPY and SUBREG_TO_REG, so we
// can also see XXPERMDI t, SUBREG_TO_REG(s), SUBREG_TO_REG(s), 2,
// for example. We have to look through chains of COPY and
// SUBREG_TO_REG to find the real source value for comparison.
// If the real source value is a physical register, then mark the
// XXPERMDI as mentioning a physical register.
int immed = MI.getOperand(3).getImm();
if (immed == 2) {
unsigned trueReg1 = lookThruCopyLike(MI.getOperand(1).getReg(),
VecIdx);
unsigned trueReg2 = lookThruCopyLike(MI.getOperand(2).getReg(),
VecIdx);
if (trueReg1 == trueReg2)
SwapVector[VecIdx].IsSwap = 1;
else {
// We can still handle these if the two registers are not
// identical, by adjusting the form of the XXPERMDI.
SwapVector[VecIdx].IsSwappable = 1;
SwapVector[VecIdx].SpecialHandling = SHValues::SH_XXPERMDI;
}
// This is a doubleword splat if it is of the form
// XXPERMDI t, s, s, 0 or XXPERMDI t, s, s, 3. As above we
// must look through chains of copy-likes to find the source
// register. We turn off the marking for mention of a physical
// register, because splatting it is safe; the optimization
// will not swap the value in the physical register. Whether
// or not the two input registers are identical, we can handle
// these by adjusting the form of the XXPERMDI.
} else if (immed == 0 || immed == 3) {
SwapVector[VecIdx].IsSwappable = 1;
SwapVector[VecIdx].SpecialHandling = SHValues::SH_XXPERMDI;
unsigned trueReg1 = lookThruCopyLike(MI.getOperand(1).getReg(),
VecIdx);
unsigned trueReg2 = lookThruCopyLike(MI.getOperand(2).getReg(),
VecIdx);
if (trueReg1 == trueReg2)
SwapVector[VecIdx].MentionsPhysVR = 0;
} else {
// We can still handle these by adjusting the form of the XXPERMDI.
SwapVector[VecIdx].IsSwappable = 1;
SwapVector[VecIdx].SpecialHandling = SHValues::SH_XXPERMDI;
}
break;
}
case PPC::LVX:
// Non-permuting loads are currently unsafe. We can use special
// handling for this in the future. By not marking these as
// IsSwap, we ensure computations containing them will be rejected
// for now.
SwapVector[VecIdx].IsLoad = 1;
break;
case PPC::LXVD2X:
case PPC::LXVW4X:
// Permuting loads are marked as both load and swap, and are
// safe for optimization.
SwapVector[VecIdx].IsLoad = 1;
SwapVector[VecIdx].IsSwap = 1;
break;
case PPC::LXSDX:
case PPC::LXSSPX:
// A load of a floating-point value into the high-order half of
// a vector register is safe, provided that we introduce a swap
// following the load, which will be done by the SUBREG_TO_REG
// support. So just mark these as safe.
SwapVector[VecIdx].IsLoad = 1;
SwapVector[VecIdx].IsSwappable = 1;
break;
case PPC::STVX:
// Non-permuting stores are currently unsafe. We can use special
// handling for this in the future. By not marking these as
// IsSwap, we ensure computations containing them will be rejected
// for now.
SwapVector[VecIdx].IsStore = 1;
break;
case PPC::STXVD2X:
case PPC::STXVW4X:
// Permuting stores are marked as both store and swap, and are
// safe for optimization.
SwapVector[VecIdx].IsStore = 1;
SwapVector[VecIdx].IsSwap = 1;
break;
case PPC::COPY:
// These are fine provided they are moving between full vector
// register classes.
if (isVecReg(MI.getOperand(0).getReg()) &&
isVecReg(MI.getOperand(1).getReg()))
SwapVector[VecIdx].IsSwappable = 1;
// If we have a copy from one scalar floating-point register
// to another, we can accept this even if it is a physical
// register. The only way this gets involved is if it feeds
// a SUBREG_TO_REG, which is handled by introducing a swap.
else if (isScalarVecReg(MI.getOperand(0).getReg()) &&
isScalarVecReg(MI.getOperand(1).getReg()))
SwapVector[VecIdx].IsSwappable = 1;
break;
case PPC::SUBREG_TO_REG: {
// These are fine provided they are moving between full vector
// register classes. If they are moving from a scalar
// floating-point class to a vector class, we can handle those
// as well, provided we introduce a swap. It is generally the
// case that we will introduce fewer swaps than we remove, but
// (FIXME) a cost model could be used. However, introduced
// swaps could potentially be CSEd, so this is not trivial.
if (isVecReg(MI.getOperand(0).getReg()) &&
isVecReg(MI.getOperand(2).getReg()))
SwapVector[VecIdx].IsSwappable = 1;
else if (isVecReg(MI.getOperand(0).getReg()) &&
isScalarVecReg(MI.getOperand(2).getReg())) {
SwapVector[VecIdx].IsSwappable = 1;
SwapVector[VecIdx].SpecialHandling = SHValues::SH_COPYWIDEN;
}
break;
}
case PPC::VSPLTB:
case PPC::VSPLTH:
case PPC::VSPLTW:
case PPC::XXSPLTW:
// Splats are lane-sensitive, but we can use special handling
// to adjust the source lane for the splat.
SwapVector[VecIdx].IsSwappable = 1;
SwapVector[VecIdx].SpecialHandling = SHValues::SH_SPLAT;
break;
// The presence of the following lane-sensitive operations in a
// web will kill the optimization, at least for now. For these
// we do nothing, causing the optimization to fail.
// FIXME: Some of these could be permitted with special handling,
// and will be phased in as time permits.
// FIXME: There is no simple and maintainable way to express a set
// of opcodes having a common attribute in TableGen. Should this
// change, this is a prime candidate to use such a mechanism.
case PPC::INLINEASM:
case PPC::EXTRACT_SUBREG:
case PPC::INSERT_SUBREG:
case PPC::COPY_TO_REGCLASS:
case PPC::LVEBX:
case PPC::LVEHX:
case PPC::LVEWX:
case PPC::LVSL:
case PPC::LVSR:
case PPC::LVXL:
case PPC::STVEBX:
case PPC::STVEHX:
case PPC::STVEWX:
case PPC::STVXL:
// We can handle STXSDX and STXSSPX similarly to LXSDX and LXSSPX,
// by adding special handling for narrowing copies as well as
// widening ones. However, I've experimented with this, and in
// practice we currently do not appear to use STXSDX fed by
// a narrowing copy from a full vector register. Since I can't
// generate any useful test cases, I've left this alone for now.
case PPC::STXSDX:
case PPC::STXSSPX:
case PPC::VCIPHER:
case PPC::VCIPHERLAST:
case PPC::VMRGHB:
case PPC::VMRGHH:
case PPC::VMRGHW:
case PPC::VMRGLB:
case PPC::VMRGLH:
case PPC::VMRGLW:
case PPC::VMULESB:
case PPC::VMULESH:
case PPC::VMULESW:
case PPC::VMULEUB:
case PPC::VMULEUH:
case PPC::VMULEUW:
case PPC::VMULOSB:
case PPC::VMULOSH:
case PPC::VMULOSW:
case PPC::VMULOUB:
case PPC::VMULOUH:
case PPC::VMULOUW:
case PPC::VNCIPHER:
case PPC::VNCIPHERLAST:
case PPC::VPERM:
case PPC::VPERMXOR:
case PPC::VPKPX:
case PPC::VPKSHSS:
case PPC::VPKSHUS:
case PPC::VPKSDSS:
case PPC::VPKSDUS:
case PPC::VPKSWSS:
case PPC::VPKSWUS:
case PPC::VPKUDUM:
case PPC::VPKUDUS:
case PPC::VPKUHUM:
case PPC::VPKUHUS:
case PPC::VPKUWUM:
case PPC::VPKUWUS:
case PPC::VPMSUMB:
case PPC::VPMSUMD:
case PPC::VPMSUMH:
case PPC::VPMSUMW:
case PPC::VRLB:
case PPC::VRLD:
case PPC::VRLH:
case PPC::VRLW:
case PPC::VSBOX:
case PPC::VSHASIGMAD:
case PPC::VSHASIGMAW:
case PPC::VSL:
case PPC::VSLDOI:
case PPC::VSLO:
case PPC::VSR:
case PPC::VSRO:
case PPC::VSUM2SWS:
case PPC::VSUM4SBS:
case PPC::VSUM4SHS:
case PPC::VSUM4UBS:
case PPC::VSUMSWS:
case PPC::VUPKHPX:
case PPC::VUPKHSB:
case PPC::VUPKHSH:
case PPC::VUPKHSW:
case PPC::VUPKLPX:
case PPC::VUPKLSB:
case PPC::VUPKLSH:
case PPC::VUPKLSW:
case PPC::XXMRGHW:
case PPC::XXMRGLW:
// XXSLDWI could be replaced by a general permute with one of three
// permute control vectors (for shift values 1, 2, 3). However,
// VPERM has a more restrictive register class.
case PPC::XXSLDWI:
break;
}
}
}
if (RelevantFunction) {
DEBUG(dbgs() << "Swap vector when first built\n\n");
dumpSwapVector();
}
return RelevantFunction;
}
// Add an entry to the swap vector and swap map, and make a
// singleton equivalence class for the entry.
int PPCVSXSwapRemoval::addSwapEntry(MachineInstr *MI,
PPCVSXSwapEntry& SwapEntry) {
SwapEntry.VSEMI = MI;
SwapEntry.VSEId = SwapVector.size();
SwapVector.push_back(SwapEntry);
EC->insert(SwapEntry.VSEId);
SwapMap[MI] = SwapEntry.VSEId;
return SwapEntry.VSEId;
}
// This is used to find the "true" source register for an
// XXPERMDI instruction, since MachineCSE does not handle the
// "copy-like" operations (Copy and SubregToReg). Returns
// the original SrcReg unless it is the target of a copy-like
// operation, in which case we chain backwards through all
// such operations to the ultimate source register. If a
// physical register is encountered, we stop the search and
// flag the swap entry indicated by VecIdx (the original
// XXPERMDI) as mentioning a physical register.
unsigned PPCVSXSwapRemoval::lookThruCopyLike(unsigned SrcReg,
unsigned VecIdx) {
MachineInstr *MI = MRI->getVRegDef(SrcReg);
if (!MI->isCopyLike())
return SrcReg;
unsigned CopySrcReg;
if (MI->isCopy())
CopySrcReg = MI->getOperand(1).getReg();
else {
assert(MI->isSubregToReg() && "bad opcode for lookThruCopyLike");
CopySrcReg = MI->getOperand(2).getReg();
}
if (!TargetRegisterInfo::isVirtualRegister(CopySrcReg)) {
if (!isScalarVecReg(CopySrcReg))
SwapVector[VecIdx].MentionsPhysVR = 1;
return CopySrcReg;
}
return lookThruCopyLike(CopySrcReg, VecIdx);
}
// Generate equivalence classes for related computations (webs) by
// def-use relationships of virtual registers. Mention of a physical
// register terminates the generation of equivalence classes as this
// indicates a use of a parameter, definition of a return value, use
// of a value returned from a call, or definition of a parameter to a
// call. Computations with physical register mentions are flagged
// as such so their containing webs will not be optimized.
void PPCVSXSwapRemoval::formWebs() {
DEBUG(dbgs() << "\n*** Forming webs for swap removal ***\n\n");
for (unsigned EntryIdx = 0; EntryIdx < SwapVector.size(); ++EntryIdx) {
MachineInstr *MI = SwapVector[EntryIdx].VSEMI;
DEBUG(dbgs() << "\n" << SwapVector[EntryIdx].VSEId << " ");
DEBUG(MI->dump());
// It's sufficient to walk vector uses and join them to their unique
// definitions. In addition, check full vector register operands
// for physical regs. We exclude partial-vector register operands
// because we can handle them if copied to a full vector.
for (const MachineOperand &MO : MI->operands()) {
if (!MO.isReg())
continue;
unsigned Reg = MO.getReg();
if (!isVecReg(Reg) && !isScalarVecReg(Reg))
continue;
if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
if (!(MI->isCopy() && isScalarVecReg(Reg)))
SwapVector[EntryIdx].MentionsPhysVR = 1;
continue;
}
if (!MO.isUse())
continue;
MachineInstr* DefMI = MRI->getVRegDef(Reg);
assert(SwapMap.find(DefMI) != SwapMap.end() &&
"Inconsistency: def of vector reg not found in swap map!");
int DefIdx = SwapMap[DefMI];
(void)EC->unionSets(SwapVector[DefIdx].VSEId,
SwapVector[EntryIdx].VSEId);
DEBUG(dbgs() << format("Unioning %d with %d\n", SwapVector[DefIdx].VSEId,
SwapVector[EntryIdx].VSEId));
DEBUG(dbgs() << " Def: ");
DEBUG(DefMI->dump());
}
}
}
// Walk the swap vector entries looking for conditions that prevent their
// containing computations from being optimized. When such conditions are
// found, mark the representative of the computation's equivalence class
// as rejected.
void PPCVSXSwapRemoval::recordUnoptimizableWebs() {
DEBUG(dbgs() << "\n*** Rejecting webs for swap removal ***\n\n");
for (unsigned EntryIdx = 0; EntryIdx < SwapVector.size(); ++EntryIdx) {
int Repr = EC->getLeaderValue(SwapVector[EntryIdx].VSEId);
// If representative is already rejected, don't waste further time.
if (SwapVector[Repr].WebRejected)
continue;
// Reject webs containing mentions of physical or partial registers, or
// containing operations that we don't know how to handle in a lane-
// permuted region.
if (SwapVector[EntryIdx].MentionsPhysVR ||
SwapVector[EntryIdx].MentionsPartialVR ||
!(SwapVector[EntryIdx].IsSwappable || SwapVector[EntryIdx].IsSwap)) {
SwapVector[Repr].WebRejected = 1;
DEBUG(dbgs() <<
format("Web %d rejected for physreg, partial reg, or not "
"swap[pable]\n", Repr));
DEBUG(dbgs() << " in " << EntryIdx << ": ");
DEBUG(SwapVector[EntryIdx].VSEMI->dump());
DEBUG(dbgs() << "\n");
}
// Reject webs than contain swapping loads that feed something other
// than a swap instruction.
else if (SwapVector[EntryIdx].IsLoad && SwapVector[EntryIdx].IsSwap) {
MachineInstr *MI = SwapVector[EntryIdx].VSEMI;
unsigned DefReg = MI->getOperand(0).getReg();
// We skip debug instructions in the analysis. (Note that debug
// location information is still maintained by this optimization
// because it remains on the LXVD2X and STXVD2X instructions after
// the XXPERMDIs are removed.)
for (MachineInstr &UseMI : MRI->use_nodbg_instructions(DefReg)) {
int UseIdx = SwapMap[&UseMI];
if (!SwapVector[UseIdx].IsSwap || SwapVector[UseIdx].IsLoad ||
SwapVector[UseIdx].IsStore) {
SwapVector[Repr].WebRejected = 1;
DEBUG(dbgs() <<
format("Web %d rejected for load not feeding swap\n", Repr));
DEBUG(dbgs() << " def " << EntryIdx << ": ");
DEBUG(MI->dump());
DEBUG(dbgs() << " use " << UseIdx << ": ");
DEBUG(UseMI.dump());
DEBUG(dbgs() << "\n");
}
}
// Reject webs that contain swapping stores that are fed by something
// other than a swap instruction.
} else if (SwapVector[EntryIdx].IsStore && SwapVector[EntryIdx].IsSwap) {
MachineInstr *MI = SwapVector[EntryIdx].VSEMI;
unsigned UseReg = MI->getOperand(0).getReg();
MachineInstr *DefMI = MRI->getVRegDef(UseReg);
unsigned DefReg = DefMI->getOperand(0).getReg();
int DefIdx = SwapMap[DefMI];
if (!SwapVector[DefIdx].IsSwap || SwapVector[DefIdx].IsLoad ||
SwapVector[DefIdx].IsStore) {
SwapVector[Repr].WebRejected = 1;
DEBUG(dbgs() <<
format("Web %d rejected for store not fed by swap\n", Repr));
DEBUG(dbgs() << " def " << DefIdx << ": ");
DEBUG(DefMI->dump());
DEBUG(dbgs() << " use " << EntryIdx << ": ");
DEBUG(MI->dump());
DEBUG(dbgs() << "\n");
}
// Ensure all uses of the register defined by DefMI feed store
// instructions
for (MachineInstr &UseMI : MRI->use_nodbg_instructions(DefReg)) {
int UseIdx = SwapMap[&UseMI];
if (SwapVector[UseIdx].VSEMI->getOpcode() != MI->getOpcode()) {
SwapVector[Repr].WebRejected = 1;
DEBUG(dbgs() <<
format("Web %d rejected for swap not feeding only stores\n",
Repr));
DEBUG(dbgs() << " def " << " : ");
DEBUG(DefMI->dump());
DEBUG(dbgs() << " use " << UseIdx << ": ");
DEBUG(SwapVector[UseIdx].VSEMI->dump());
DEBUG(dbgs() << "\n");
}
}
}
}
DEBUG(dbgs() << "Swap vector after web analysis:\n\n");
dumpSwapVector();
}
// Walk the swap vector entries looking for swaps fed by permuting loads
// and swaps that feed permuting stores. If the containing computation
// has not been marked rejected, mark each such swap for removal.
// (Removal is delayed in case optimization has disturbed the pattern,
// such that multiple loads feed the same swap, etc.)
void PPCVSXSwapRemoval::markSwapsForRemoval() {
DEBUG(dbgs() << "\n*** Marking swaps for removal ***\n\n");
for (unsigned EntryIdx = 0; EntryIdx < SwapVector.size(); ++EntryIdx) {
if (SwapVector[EntryIdx].IsLoad && SwapVector[EntryIdx].IsSwap) {
int Repr = EC->getLeaderValue(SwapVector[EntryIdx].VSEId);
if (!SwapVector[Repr].WebRejected) {
MachineInstr *MI = SwapVector[EntryIdx].VSEMI;
unsigned DefReg = MI->getOperand(0).getReg();
for (MachineInstr &UseMI : MRI->use_nodbg_instructions(DefReg)) {
int UseIdx = SwapMap[&UseMI];
SwapVector[UseIdx].WillRemove = 1;
DEBUG(dbgs() << "Marking swap fed by load for removal: ");
DEBUG(UseMI.dump());
}
}
} else if (SwapVector[EntryIdx].IsStore && SwapVector[EntryIdx].IsSwap) {
int Repr = EC->getLeaderValue(SwapVector[EntryIdx].VSEId);
if (!SwapVector[Repr].WebRejected) {
MachineInstr *MI = SwapVector[EntryIdx].VSEMI;
unsigned UseReg = MI->getOperand(0).getReg();
MachineInstr *DefMI = MRI->getVRegDef(UseReg);
int DefIdx = SwapMap[DefMI];
SwapVector[DefIdx].WillRemove = 1;
DEBUG(dbgs() << "Marking swap feeding store for removal: ");
DEBUG(DefMI->dump());
}
} else if (SwapVector[EntryIdx].IsSwappable &&
SwapVector[EntryIdx].SpecialHandling != 0) {
int Repr = EC->getLeaderValue(SwapVector[EntryIdx].VSEId);
if (!SwapVector[Repr].WebRejected)
handleSpecialSwappables(EntryIdx);
}
}
}
// Create an xxswapd instruction and insert it prior to the given point.
// MI is used to determine basic block and debug loc information.
// FIXME: When inserting a swap, we should check whether SrcReg is
// defined by another swap: SrcReg = XXPERMDI Reg, Reg, 2; If so,
// then instead we should generate a copy from Reg to DstReg.
void PPCVSXSwapRemoval::insertSwap(MachineInstr *MI,
MachineBasicBlock::iterator InsertPoint,
unsigned DstReg, unsigned SrcReg) {
BuildMI(*MI->getParent(), InsertPoint, MI->getDebugLoc(),
TII->get(PPC::XXPERMDI), DstReg)
.addReg(SrcReg)
.addReg(SrcReg)
.addImm(2);
}
// The identified swap entry requires special handling to allow its
// containing computation to be optimized. Perform that handling
// here.
// FIXME: Additional opportunities will be phased in with subsequent
// patches.
void PPCVSXSwapRemoval::handleSpecialSwappables(int EntryIdx) {
switch (SwapVector[EntryIdx].SpecialHandling) {
default:
llvm_unreachable("Unexpected special handling type");
// For splats based on an index into a vector, add N/2 modulo N
// to the index, where N is the number of vector elements.
case SHValues::SH_SPLAT: {
MachineInstr *MI = SwapVector[EntryIdx].VSEMI;
unsigned NElts;
DEBUG(dbgs() << "Changing splat: ");
DEBUG(MI->dump());
switch (MI->getOpcode()) {
default:
llvm_unreachable("Unexpected splat opcode");
case PPC::VSPLTB: NElts = 16; break;
case PPC::VSPLTH: NElts = 8; break;
case PPC::VSPLTW:
case PPC::XXSPLTW: NElts = 4; break;
}
unsigned EltNo;
if (MI->getOpcode() == PPC::XXSPLTW)
EltNo = MI->getOperand(2).getImm();
else
EltNo = MI->getOperand(1).getImm();
EltNo = (EltNo + NElts / 2) % NElts;
if (MI->getOpcode() == PPC::XXSPLTW)
MI->getOperand(2).setImm(EltNo);
else
MI->getOperand(1).setImm(EltNo);
DEBUG(dbgs() << " Into: ");
DEBUG(MI->dump());
break;
}
// For an XXPERMDI that isn't handled otherwise, we need to
// reverse the order of the operands. If the selector operand
// has a value of 0 or 3, we need to change it to 3 or 0,
// respectively. Otherwise we should leave it alone. (This
// is equivalent to reversing the two bits of the selector
// operand and complementing the result.)
case SHValues::SH_XXPERMDI: {
MachineInstr *MI = SwapVector[EntryIdx].VSEMI;
DEBUG(dbgs() << "Changing XXPERMDI: ");
DEBUG(MI->dump());
unsigned Selector = MI->getOperand(3).getImm();
if (Selector == 0 || Selector == 3)
Selector = 3 - Selector;
MI->getOperand(3).setImm(Selector);
unsigned Reg1 = MI->getOperand(1).getReg();
unsigned Reg2 = MI->getOperand(2).getReg();
MI->getOperand(1).setReg(Reg2);
MI->getOperand(2).setReg(Reg1);
DEBUG(dbgs() << " Into: ");
DEBUG(MI->dump());
break;
}
// For a copy from a scalar floating-point register to a vector
// register, removing swaps will leave the copied value in the
// wrong lane. Insert a swap following the copy to fix this.
case SHValues::SH_COPYWIDEN: {
MachineInstr *MI = SwapVector[EntryIdx].VSEMI;
DEBUG(dbgs() << "Changing SUBREG_TO_REG: ");
DEBUG(MI->dump());
unsigned DstReg = MI->getOperand(0).getReg();
const TargetRegisterClass *DstRC = MRI->getRegClass(DstReg);
unsigned NewVReg = MRI->createVirtualRegister(DstRC);
MI->getOperand(0).setReg(NewVReg);
DEBUG(dbgs() << " Into: ");
DEBUG(MI->dump());
auto InsertPoint = ++MachineBasicBlock::iterator(MI);
// Note that an XXPERMDI requires a VSRC, so if the SUBREG_TO_REG
// is copying to a VRRC, we need to be careful to avoid a register
// assignment problem. In this case we must copy from VRRC to VSRC
// prior to the swap, and from VSRC to VRRC following the swap.
// Coalescing will usually remove all this mess.
if (DstRC == &PPC::VRRCRegClass) {
unsigned VSRCTmp1 = MRI->createVirtualRegister(&PPC::VSRCRegClass);
unsigned VSRCTmp2 = MRI->createVirtualRegister(&PPC::VSRCRegClass);
BuildMI(*MI->getParent(), InsertPoint, MI->getDebugLoc(),
TII->get(PPC::COPY), VSRCTmp1)
.addReg(NewVReg);
DEBUG(std::prev(InsertPoint)->dump());
insertSwap(MI, InsertPoint, VSRCTmp2, VSRCTmp1);
DEBUG(std::prev(InsertPoint)->dump());
BuildMI(*MI->getParent(), InsertPoint, MI->getDebugLoc(),
TII->get(PPC::COPY), DstReg)
.addReg(VSRCTmp2);
DEBUG(std::prev(InsertPoint)->dump());
} else {
insertSwap(MI, InsertPoint, DstReg, NewVReg);
DEBUG(std::prev(InsertPoint)->dump());
}
break;
}
}
}
// Walk the swap vector and replace each entry marked for removal with
// a copy operation.
bool PPCVSXSwapRemoval::removeSwaps() {
DEBUG(dbgs() << "\n*** Removing swaps ***\n\n");
bool Changed = false;
for (unsigned EntryIdx = 0; EntryIdx < SwapVector.size(); ++EntryIdx) {
if (SwapVector[EntryIdx].WillRemove) {
Changed = true;
MachineInstr *MI = SwapVector[EntryIdx].VSEMI;
MachineBasicBlock *MBB = MI->getParent();
BuildMI(*MBB, MI, MI->getDebugLoc(),
TII->get(TargetOpcode::COPY), MI->getOperand(0).getReg())
.addOperand(MI->getOperand(1));
DEBUG(dbgs() << format("Replaced %d with copy: ",
SwapVector[EntryIdx].VSEId));
DEBUG(MI->dump());
MI->eraseFromParent();
}
}
return Changed;
}
// For debug purposes, dump the contents of the swap vector.
void PPCVSXSwapRemoval::dumpSwapVector() {
for (unsigned EntryIdx = 0; EntryIdx < SwapVector.size(); ++EntryIdx) {
MachineInstr *MI = SwapVector[EntryIdx].VSEMI;
int ID = SwapVector[EntryIdx].VSEId;
DEBUG(dbgs() << format("%6d", ID));
DEBUG(dbgs() << format("%6d", EC->getLeaderValue(ID)));
DEBUG(dbgs() << format(" BB#%3d", MI->getParent()->getNumber()));
DEBUG(dbgs() << format(" %14s ", TII->getName(MI->getOpcode())));
if (SwapVector[EntryIdx].IsLoad)
DEBUG(dbgs() << "load ");
if (SwapVector[EntryIdx].IsStore)
DEBUG(dbgs() << "store ");
if (SwapVector[EntryIdx].IsSwap)
DEBUG(dbgs() << "swap ");
if (SwapVector[EntryIdx].MentionsPhysVR)
DEBUG(dbgs() << "physreg ");
if (SwapVector[EntryIdx].MentionsPartialVR)
DEBUG(dbgs() << "partialreg ");
if (SwapVector[EntryIdx].IsSwappable) {
DEBUG(dbgs() << "swappable ");
switch(SwapVector[EntryIdx].SpecialHandling) {
default:
DEBUG(dbgs() << "special:**unknown**");
break;
case SH_NONE:
break;
case SH_EXTRACT:
DEBUG(dbgs() << "special:extract ");
break;
case SH_INSERT:
DEBUG(dbgs() << "special:insert ");
break;
case SH_NOSWAP_LD:
DEBUG(dbgs() << "special:load ");
break;
case SH_NOSWAP_ST:
DEBUG(dbgs() << "special:store ");
break;
case SH_SPLAT:
DEBUG(dbgs() << "special:splat ");
break;
case SH_XXPERMDI:
DEBUG(dbgs() << "special:xxpermdi ");
break;
case SH_COPYWIDEN:
DEBUG(dbgs() << "special:copywiden ");
break;
}
}
if (SwapVector[EntryIdx].WebRejected)
DEBUG(dbgs() << "rejected ");
if (SwapVector[EntryIdx].WillRemove)
DEBUG(dbgs() << "remove ");
DEBUG(dbgs() << "\n");
// For no-asserts builds.
(void)MI;
(void)ID;
}
DEBUG(dbgs() << "\n");
}
} // end default namespace
INITIALIZE_PASS_BEGIN(PPCVSXSwapRemoval, DEBUG_TYPE,
"PowerPC VSX Swap Removal", false, false)
INITIALIZE_PASS_END(PPCVSXSwapRemoval, DEBUG_TYPE,
"PowerPC VSX Swap Removal", false, false)
char PPCVSXSwapRemoval::ID = 0;
FunctionPass*
llvm::createPPCVSXSwapRemovalPass() { return new PPCVSXSwapRemoval(); }
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