[llvm] r342942 - [MachineCopyPropagation] Reimplement CopyTracker in terms of register units
Mikael Holmén via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 26 07:21:16 PDT 2018
I made a small mir-reproducer for my target:
---
name: f
tracksRegLiveness: true
body: |
bb.0:
nop 0, $noreg, 0, implicit-def $a5_40
$a6_40 = COPY killed $a5_40
$a5_40 = COPY killed $a6_40
nop 0, $noreg, 0, implicit-def $a6h
nop 0, $noreg, 0, implicit killed $a6h
$a6_40 = COPY killed $a5_40
$a0_40 = COPY $a6_40
nop 0, $noreg, 0, implicit $a0_40
...
If I just run machine-cp on the above:
llc -mtriple phoenix -o - foo.mir -run-pass=machine-cp -debug
I get
MCP: CopyPropagateBlock
MCP: Copy is a deletion candidate: $a6_40 = COPY killed $a5_40
MCP: copy is a NOP, removing: $a5_40 = COPY killed $a6_40
MCP: copy is a NOP, removing: $a6_40 = COPY killed $a5_40
MCP: Copy is used - not dead: $a6_40 = COPY $a5_40
MCP: Copy is used - not dead: $a6_40 = COPY $a5_40
MCP: Copy is a deletion candidate: $a0_40 = COPY $a6_40
MCP: Copy is used - not dead: $a0_40 = COPY $a6_40
MCP: Copy is used - not dead: $a0_40 = COPY $a6_40
MCP: Copy is used - not dead: $a0_40 = COPY $a6_40
and the result
body: |
bb.0:
nop 0, $noreg, 0, implicit-def $a5_40
$a6_40 = COPY $a5_40
nop 0, $noreg, 0, implicit-def $a6h
nop 0, $noreg, 0, implicit $a6h
$a0_40 = COPY $a6_40
nop 0, $noreg, 0, implicit $a0_40
The register $a6_40 is made up of $a6_32 and $a6_g, and $a6_32 in turn
is made up of $a6h and $a6l so $a6_40 and $a6h overlap.
I would like to convert the mir-reproducer to some in-tree target but I
must run now so it'll be tomorrow.
/Mikael
On 09/26/2018 03:08 PM, Mikael Holmén via llvm-commits wrote:
> Hi Justin,
>
> I have a case for my out-of-tree target where MCP now removes a COPY
> that is needed.
>
> Unfortunately the input is huge so I need to fiddle with it for a while
> to get it reduced to something manageble but I thought I'd give a heads up.
>
> I think it's something like
>
> $a5_40 = COPY killed $a6_40
>
> [...]
>
> $a6h = <instr1>
> <instr2> killed $a6h
>
> [...]
>
> $a6_40 = COPY killed $a5_40
> $a0_40 = COPY $a6_40
> <instr3> killed $a0_40
>
> and MCP decides that
>
> MCP: copy is a NOP, removing: $a6_40 = COPY killed $a5_40
>
> but it's not since a part of $a6_40 was overwritten, so if we remove the
> COPY from $a5_40 to $a6_40 the $a6h part of $a6_40 will contain garbage.
>
> Are you aware of anything in the change that could possibly lead to this?
>
> Regards,
> Mikael
>
> On 09/25/2018 07:16 AM, Justin Bogner via llvm-commits wrote:
>> Author: bogner
>> Date: Mon Sep 24 22:16:44 2018
>> New Revision: 342942
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=342942&view=rev
>> Log:
>> [MachineCopyPropagation] Reimplement CopyTracker in terms of register
>> units
>>
>> Change the copy tracker to keep a single map of register units instead
>> of 3 maps of registers. This gives a very significant compile time
>> performance improvement to the pass. I measured a 30-40% decrease in
>> time spent in MCP on x86 and AArch64 and much more significant
>> improvements on out of tree targets with more registers.
>>
>> Differential Revision: https://reviews.llvm.org/D52374
>>
>> Modified:
>> llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp
>>
>> Modified: llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp?rev=342942&r1=342941&r2=342942&view=diff
>>
>> ==============================================================================
>>
>> --- llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp (original)
>> +++ llvm/trunk/lib/CodeGen/MachineCopyPropagation.cpp Mon Sep 24
>> 22:16:44 2018
>> @@ -75,40 +75,36 @@ DEBUG_COUNTER(FwdCounter, "machine-cp-fw
>> namespace {
>> class CopyTracker {
>> - using RegList = SmallVector<unsigned, 4>;
>> - using SourceMap = DenseMap<unsigned, RegList>;
>> - using Reg2MIMap = DenseMap<unsigned, MachineInstr *>;
>> + struct CopyInfo {
>> + MachineInstr *MI;
>> + SmallVector<unsigned, 4> DefRegs;
>> + bool Avail;
>> + };
>> - /// Def -> available copies map.
>> - Reg2MIMap AvailCopyMap;
>> -
>> - /// Def -> copies map.
>> - Reg2MIMap CopyMap;
>> -
>> - /// Src -> Def map
>> - SourceMap SrcMap;
>> + DenseMap<unsigned, CopyInfo> Copies;
>> public:
>> /// Mark all of the given registers and their subregisters as
>> unavailable for
>> /// copying.
>> - void markRegsUnavailable(const RegList &Regs, const
>> TargetRegisterInfo &TRI) {
>> + void markRegsUnavailable(ArrayRef<unsigned> Regs,
>> + const TargetRegisterInfo &TRI) {
>> for (unsigned Reg : Regs) {
>> // Source of copy is no longer available for propagation.
>> - for (MCSubRegIterator SR(Reg, &TRI, true); SR.isValid(); ++SR)
>> - AvailCopyMap.erase(*SR);
>> + for (MCRegUnitIterator RUI(Reg, &TRI); RUI.isValid(); ++RUI) {
>> + auto CI = Copies.find(*RUI);
>> + if (CI != Copies.end())
>> + CI->second.Avail = false;
>> + }
>> }
>> }
>> /// Clobber a single register, removing it from the tracker's copy
>> maps.
>> void clobberRegister(unsigned Reg, const TargetRegisterInfo &TRI) {
>> - for (MCRegAliasIterator AI(Reg, &TRI, true); AI.isValid(); ++AI) {
>> - CopyMap.erase(*AI);
>> - AvailCopyMap.erase(*AI);
>> -
>> - SourceMap::iterator SI = SrcMap.find(*AI);
>> - if (SI != SrcMap.end()) {
>> - markRegsUnavailable(SI->second, TRI);
>> - SrcMap.erase(SI);
>> + for (MCRegUnitIterator RUI(Reg, &TRI); RUI.isValid(); ++RUI) {
>> + auto I = Copies.find(*RUI);
>> + if (I != Copies.end()) {
>> + markRegsUnavailable(I->second.DefRegs, TRI);
>> + Copies.erase(I);
>> }
>> }
>> }
>> @@ -121,52 +117,60 @@ public:
>> unsigned Src = Copy->getOperand(1).getReg();
>> // Remember Def is defined by the copy.
>> - for (MCSubRegIterator SR(Def, &TRI, /*IncludeSelf=*/true);
>> SR.isValid();
>> - ++SR) {
>> - CopyMap[*SR] = Copy;
>> - AvailCopyMap[*SR] = Copy;
>> - }
>> + for (MCRegUnitIterator RUI(Def, &TRI); RUI.isValid(); ++RUI)
>> + Copies[*RUI] = {Copy, {}, true};
>> // Remember source that's copied to Def. Once it's clobbered, then
>> // it's no longer available for copy propagation.
>> - RegList &DestList = SrcMap[Src];
>> - if (!is_contained(DestList, Def))
>> - DestList.push_back(Def);
>> + for (MCRegUnitIterator RUI(Src, &TRI); RUI.isValid(); ++RUI) {
>> + auto I = Copies.insert({*RUI, {nullptr, {}, false}});
>> + auto &Copy = I.first->second;
>> + if (!is_contained(Copy.DefRegs, Def))
>> + Copy.DefRegs.push_back(Def);
>> + }
>> + }
>> +
>> + bool hasAnyCopies() {
>> + return !Copies.empty();
>> }
>> - bool hasAvailableCopies() { return !AvailCopyMap.empty(); }
>> + MachineInstr *findCopyForUnit(unsigned RegUnit, const
>> TargetRegisterInfo &TRI,
>> + bool MustBeAvailable = false) {
>> + auto CI = Copies.find(RegUnit);
>> + if (CI == Copies.end())
>> + return nullptr;
>> + if (MustBeAvailable && !CI->second.Avail)
>> + return nullptr;
>> + return CI->second.MI;
>> + }
>> - MachineInstr *findAvailCopy(MachineInstr &DestCopy, unsigned Reg) {
>> - auto CI = AvailCopyMap.find(Reg);
>> - if (CI == AvailCopyMap.end())
>> + MachineInstr *findAvailCopy(MachineInstr &DestCopy, unsigned Reg,
>> + const TargetRegisterInfo &TRI) {
>> + // We check the first RegUnit here, since we'll only be
>> interested in the
>> + // copy if it copies the entire register anyway.
>> + MCRegUnitIterator RUI(Reg, &TRI);
>> + MachineInstr *AvailCopy =
>> + findCopyForUnit(*RUI, TRI, /*MustBeAvailable=*/true);
>> + if (!AvailCopy ||
>> + !TRI.isSubRegisterEq(AvailCopy->getOperand(0).getReg(), Reg))
>> return nullptr;
>> - MachineInstr &AvailCopy = *CI->second;
>> // Check that the available copy isn't clobbered by any regmasks
>> between
>> // itself and the destination.
>> - unsigned AvailSrc = AvailCopy.getOperand(1).getReg();
>> - unsigned AvailDef = AvailCopy.getOperand(0).getReg();
>> + unsigned AvailSrc = AvailCopy->getOperand(1).getReg();
>> + unsigned AvailDef = AvailCopy->getOperand(0).getReg();
>> for (const MachineInstr &MI :
>> - make_range(AvailCopy.getIterator(), DestCopy.getIterator()))
>> + make_range(AvailCopy->getIterator(), DestCopy.getIterator()))
>> for (const MachineOperand &MO : MI.operands())
>> if (MO.isRegMask())
>> if (MO.clobbersPhysReg(AvailSrc) ||
>> MO.clobbersPhysReg(AvailDef))
>> return nullptr;
>> - return &AvailCopy;
>> - }
>> -
>> - MachineInstr *findCopy(unsigned Reg) {
>> - auto CI = CopyMap.find(Reg);
>> - if (CI != CopyMap.end())
>> - return CI->second;
>> - return nullptr;
>> + return AvailCopy;
>> }
>> void clear() {
>> - AvailCopyMap.clear();
>> - CopyMap.clear();
>> - SrcMap.clear();
>> + Copies.clear();
>> }
>> };
>> @@ -224,8 +228,8 @@ INITIALIZE_PASS(MachineCopyPropagation,
>> void MachineCopyPropagation::ReadRegister(unsigned Reg) {
>> // If 'Reg' is defined by a copy, the copy is no longer a candidate
>> // for elimination.
>> - for (MCRegAliasIterator AI(Reg, TRI, true); AI.isValid(); ++AI) {
>> - if (MachineInstr *Copy = Tracker.findCopy(*AI)) {
>> + for (MCRegUnitIterator RUI(Reg, TRI); RUI.isValid(); ++RUI) {
>> + if (MachineInstr *Copy = Tracker.findCopyForUnit(*RUI, *TRI)) {
>> LLVM_DEBUG(dbgs() << "MCP: Copy is used - not dead: ";
>> Copy->dump());
>> MaybeDeadCopies.remove(Copy);
>> }
>> @@ -263,7 +267,7 @@ bool MachineCopyPropagation::eraseIfRedu
>> return false;
>> // Search for an existing copy.
>> - MachineInstr *PrevCopy = Tracker.findAvailCopy(Copy, Def);
>> + MachineInstr *PrevCopy = Tracker.findAvailCopy(Copy, Def, *TRI);
>> if (!PrevCopy)
>> return false;
>> @@ -357,7 +361,7 @@ bool MachineCopyPropagation::hasImplicit
>> /// Look for available copies whose destination register is used by
>> \p MI and
>> /// replace the use in \p MI with the copy's source register.
>> void MachineCopyPropagation::forwardUses(MachineInstr &MI) {
>> - if (!Tracker.hasAvailableCopies())
>> + if (!Tracker.hasAnyCopies())
>> return;
>> // Look for non-tied explicit vreg uses that have an active COPY
>> @@ -384,7 +388,7 @@ void MachineCopyPropagation::forwardUses
>> if (!MOUse.isRenamable())
>> continue;
>> - MachineInstr *Copy = Tracker.findAvailCopy(MI, MOUse.getReg());
>> + MachineInstr *Copy = Tracker.findAvailCopy(MI, MOUse.getReg(),
>> *TRI);
>> if (!Copy)
>> continue;
>>
>>
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>>
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