mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-23 17:29:19 +00:00
doing a lookup on the TargetMachine. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229995 91177308-0d34-0410-b5e6-96231b3b80d8
481 lines
16 KiB
C++
481 lines
16 KiB
C++
//===----- X86CallFrameOptimization.cpp - Optimize x86 call sequences -----===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// This file defines a pass that optimizes call sequences on x86.
|
|
// Currently, it converts movs of function parameters onto the stack into
|
|
// pushes. This is beneficial for two main reasons:
|
|
// 1) The push instruction encoding is much smaller than an esp-relative mov
|
|
// 2) It is possible to push memory arguments directly. So, if the
|
|
// the transformation is preformed pre-reg-alloc, it can help relieve
|
|
// register pressure.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include <algorithm>
|
|
|
|
#include "X86.h"
|
|
#include "X86InstrInfo.h"
|
|
#include "X86Subtarget.h"
|
|
#include "X86MachineFunctionInfo.h"
|
|
#include "llvm/ADT/Statistic.h"
|
|
#include "llvm/CodeGen/MachineFunctionPass.h"
|
|
#include "llvm/CodeGen/MachineInstrBuilder.h"
|
|
#include "llvm/CodeGen/MachineRegisterInfo.h"
|
|
#include "llvm/CodeGen/Passes.h"
|
|
#include "llvm/IR/Function.h"
|
|
#include "llvm/Support/Debug.h"
|
|
#include "llvm/Support/raw_ostream.h"
|
|
#include "llvm/Target/TargetInstrInfo.h"
|
|
|
|
using namespace llvm;
|
|
|
|
#define DEBUG_TYPE "x86-cf-opt"
|
|
|
|
static cl::opt<bool>
|
|
NoX86CFOpt("no-x86-call-frame-opt",
|
|
cl::desc("Avoid optimizing x86 call frames for size"),
|
|
cl::init(false), cl::Hidden);
|
|
|
|
namespace {
|
|
class X86CallFrameOptimization : public MachineFunctionPass {
|
|
public:
|
|
X86CallFrameOptimization() : MachineFunctionPass(ID) {}
|
|
|
|
bool runOnMachineFunction(MachineFunction &MF) override;
|
|
|
|
private:
|
|
// Information we know about a particular call site
|
|
struct CallContext {
|
|
CallContext()
|
|
: Call(nullptr), SPCopy(nullptr), ExpectedDist(0),
|
|
MovVector(4, nullptr), NoStackParams(false), UsePush(false){};
|
|
|
|
// Actuall call instruction
|
|
MachineInstr *Call;
|
|
|
|
// A copy of the stack pointer
|
|
MachineInstr *SPCopy;
|
|
|
|
// The total displacement of all passed parameters
|
|
int64_t ExpectedDist;
|
|
|
|
// The sequence of movs used to pass the parameters
|
|
SmallVector<MachineInstr *, 4> MovVector;
|
|
|
|
// True if this call site has no stack parameters
|
|
bool NoStackParams;
|
|
|
|
// True of this callsite can use push instructions
|
|
bool UsePush;
|
|
};
|
|
|
|
typedef DenseMap<MachineInstr *, CallContext> ContextMap;
|
|
|
|
bool isLegal(MachineFunction &MF);
|
|
|
|
bool isProfitable(MachineFunction &MF, ContextMap &CallSeqMap);
|
|
|
|
void collectCallInfo(MachineFunction &MF, MachineBasicBlock &MBB,
|
|
MachineBasicBlock::iterator I, CallContext &Context);
|
|
|
|
bool adjustCallSequence(MachineFunction &MF, MachineBasicBlock::iterator I,
|
|
const CallContext &Context);
|
|
|
|
MachineInstr *canFoldIntoRegPush(MachineBasicBlock::iterator FrameSetup,
|
|
unsigned Reg);
|
|
|
|
const char *getPassName() const override { return "X86 Optimize Call Frame"; }
|
|
|
|
const TargetInstrInfo *TII;
|
|
const TargetFrameLowering *TFL;
|
|
const MachineRegisterInfo *MRI;
|
|
static char ID;
|
|
};
|
|
|
|
char X86CallFrameOptimization::ID = 0;
|
|
}
|
|
|
|
FunctionPass *llvm::createX86CallFrameOptimization() {
|
|
return new X86CallFrameOptimization();
|
|
}
|
|
|
|
// This checks whether the transformation is legal.
|
|
// Also returns false in cases where it's potentially legal, but
|
|
// we don't even want to try.
|
|
bool X86CallFrameOptimization::isLegal(MachineFunction &MF) {
|
|
if (NoX86CFOpt.getValue())
|
|
return false;
|
|
|
|
// We currently only support call sequences where *all* parameters.
|
|
// are passed on the stack.
|
|
// No point in running this in 64-bit mode, since some arguments are
|
|
// passed in-register in all common calling conventions, so the pattern
|
|
// we're looking for will never match.
|
|
const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
|
|
if (STI.is64Bit())
|
|
return false;
|
|
|
|
// You would expect straight-line code between call-frame setup and
|
|
// call-frame destroy. You would be wrong. There are circumstances (e.g.
|
|
// CMOV_GR8 expansion of a select that feeds a function call!) where we can
|
|
// end up with the setup and the destroy in different basic blocks.
|
|
// This is bad, and breaks SP adjustment.
|
|
// So, check that all of the frames in the function are closed inside
|
|
// the same block, and, for good measure, that there are no nested frames.
|
|
int FrameSetupOpcode = TII->getCallFrameSetupOpcode();
|
|
int FrameDestroyOpcode = TII->getCallFrameDestroyOpcode();
|
|
for (MachineBasicBlock &BB : MF) {
|
|
bool InsideFrameSequence = false;
|
|
for (MachineInstr &MI : BB) {
|
|
if (MI.getOpcode() == FrameSetupOpcode) {
|
|
if (InsideFrameSequence)
|
|
return false;
|
|
InsideFrameSequence = true;
|
|
} else if (MI.getOpcode() == FrameDestroyOpcode) {
|
|
if (!InsideFrameSequence)
|
|
return false;
|
|
InsideFrameSequence = false;
|
|
}
|
|
}
|
|
|
|
if (InsideFrameSequence)
|
|
return false;
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
// Check whether this trasnformation is profitable for a particular
|
|
// function - in terms of code size.
|
|
bool X86CallFrameOptimization::isProfitable(MachineFunction &MF,
|
|
ContextMap &CallSeqMap) {
|
|
// This transformation is always a win when we do not expect to have
|
|
// a reserved call frame. Under other circumstances, it may be either
|
|
// a win or a loss, and requires a heuristic.
|
|
bool CannotReserveFrame = MF.getFrameInfo()->hasVarSizedObjects();
|
|
if (CannotReserveFrame)
|
|
return true;
|
|
|
|
// Don't do this when not optimizing for size.
|
|
bool OptForSize =
|
|
MF.getFunction()->hasFnAttribute(Attribute::OptimizeForSize) ||
|
|
MF.getFunction()->hasFnAttribute(Attribute::MinSize);
|
|
|
|
if (!OptForSize)
|
|
return false;
|
|
|
|
|
|
unsigned StackAlign = TFL->getStackAlignment();
|
|
|
|
int64_t Advantage = 0;
|
|
for (auto CC : CallSeqMap) {
|
|
// Call sites where no parameters are passed on the stack
|
|
// do not affect the cost, since there needs to be no
|
|
// stack adjustment.
|
|
if (CC.second.NoStackParams)
|
|
continue;
|
|
|
|
if (!CC.second.UsePush) {
|
|
// If we don't use pushes for a particular call site,
|
|
// we pay for not having a reserved call frame with an
|
|
// additional sub/add esp pair. The cost is ~3 bytes per instruction,
|
|
// depending on the size of the constant.
|
|
// TODO: Callee-pop functions should have a smaller penalty, because
|
|
// an add is needed even with a reserved call frame.
|
|
Advantage -= 6;
|
|
} else {
|
|
// We can use pushes. First, account for the fixed costs.
|
|
// We'll need a add after the call.
|
|
Advantage -= 3;
|
|
// If we have to realign the stack, we'll also need and sub before
|
|
if (CC.second.ExpectedDist % StackAlign)
|
|
Advantage -= 3;
|
|
// Now, for each push, we save ~3 bytes. For small constants, we actually,
|
|
// save more (up to 5 bytes), but 3 should be a good approximation.
|
|
Advantage += (CC.second.ExpectedDist / 4) * 3;
|
|
}
|
|
}
|
|
|
|
return (Advantage >= 0);
|
|
}
|
|
|
|
|
|
bool X86CallFrameOptimization::runOnMachineFunction(MachineFunction &MF) {
|
|
TII = MF.getSubtarget().getInstrInfo();
|
|
TFL = MF.getSubtarget().getFrameLowering();
|
|
MRI = &MF.getRegInfo();
|
|
|
|
if (!isLegal(MF))
|
|
return false;
|
|
|
|
int FrameSetupOpcode = TII->getCallFrameSetupOpcode();
|
|
|
|
bool Changed = false;
|
|
|
|
ContextMap CallSeqMap;
|
|
|
|
for (MachineFunction::iterator BB = MF.begin(), E = MF.end(); BB != E; ++BB)
|
|
for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I)
|
|
if (I->getOpcode() == FrameSetupOpcode) {
|
|
CallContext &Context = CallSeqMap[I];
|
|
collectCallInfo(MF, *BB, I, Context);
|
|
}
|
|
|
|
if (!isProfitable(MF, CallSeqMap))
|
|
return false;
|
|
|
|
for (auto CC : CallSeqMap)
|
|
if (CC.second.UsePush)
|
|
Changed |= adjustCallSequence(MF, CC.first, CC.second);
|
|
|
|
return Changed;
|
|
}
|
|
|
|
void X86CallFrameOptimization::collectCallInfo(MachineFunction &MF,
|
|
MachineBasicBlock &MBB,
|
|
MachineBasicBlock::iterator I,
|
|
CallContext &Context) {
|
|
// Check that this particular call sequence is amenable to the
|
|
// transformation.
|
|
const X86RegisterInfo &RegInfo = *static_cast<const X86RegisterInfo *>(
|
|
MF.getSubtarget().getRegisterInfo());
|
|
unsigned StackPtr = RegInfo.getStackRegister();
|
|
int FrameDestroyOpcode = TII->getCallFrameDestroyOpcode();
|
|
|
|
// We expect to enter this at the beginning of a call sequence
|
|
assert(I->getOpcode() == TII->getCallFrameSetupOpcode());
|
|
MachineBasicBlock::iterator FrameSetup = I++;
|
|
|
|
// How much do we adjust the stack? This puts an upper bound on
|
|
// the number of parameters actually passed on it.
|
|
unsigned int MaxAdjust = FrameSetup->getOperand(0).getImm() / 4;
|
|
|
|
// A zero adjustment means no stack parameters
|
|
if (!MaxAdjust) {
|
|
Context.NoStackParams = true;
|
|
return;
|
|
}
|
|
|
|
// For globals in PIC mode, we can have some LEAs here.
|
|
// Ignore them, they don't bother us.
|
|
// TODO: Extend this to something that covers more cases.
|
|
while (I->getOpcode() == X86::LEA32r)
|
|
++I;
|
|
|
|
// We expect a copy instruction here.
|
|
// TODO: The copy instruction is a lowering artifact.
|
|
// We should also support a copy-less version, where the stack
|
|
// pointer is used directly.
|
|
if (!I->isCopy() || !I->getOperand(0).isReg())
|
|
return;
|
|
Context.SPCopy = I++;
|
|
StackPtr = Context.SPCopy->getOperand(0).getReg();
|
|
|
|
// Scan the call setup sequence for the pattern we're looking for.
|
|
// We only handle a simple case - a sequence of MOV32mi or MOV32mr
|
|
// instructions, that push a sequence of 32-bit values onto the stack, with
|
|
// no gaps between them.
|
|
if (MaxAdjust > 4)
|
|
Context.MovVector.resize(MaxAdjust, nullptr);
|
|
|
|
do {
|
|
int Opcode = I->getOpcode();
|
|
if (Opcode != X86::MOV32mi && Opcode != X86::MOV32mr)
|
|
break;
|
|
|
|
// We only want movs of the form:
|
|
// movl imm/r32, k(%esp)
|
|
// If we run into something else, bail.
|
|
// Note that AddrBaseReg may, counter to its name, not be a register,
|
|
// but rather a frame index.
|
|
// TODO: Support the fi case. This should probably work now that we
|
|
// have the infrastructure to track the stack pointer within a call
|
|
// sequence.
|
|
if (!I->getOperand(X86::AddrBaseReg).isReg() ||
|
|
(I->getOperand(X86::AddrBaseReg).getReg() != StackPtr) ||
|
|
!I->getOperand(X86::AddrScaleAmt).isImm() ||
|
|
(I->getOperand(X86::AddrScaleAmt).getImm() != 1) ||
|
|
(I->getOperand(X86::AddrIndexReg).getReg() != X86::NoRegister) ||
|
|
(I->getOperand(X86::AddrSegmentReg).getReg() != X86::NoRegister) ||
|
|
!I->getOperand(X86::AddrDisp).isImm())
|
|
return;
|
|
|
|
int64_t StackDisp = I->getOperand(X86::AddrDisp).getImm();
|
|
assert(StackDisp >= 0 &&
|
|
"Negative stack displacement when passing parameters");
|
|
|
|
// We really don't want to consider the unaligned case.
|
|
if (StackDisp % 4)
|
|
return;
|
|
StackDisp /= 4;
|
|
|
|
assert((size_t)StackDisp < Context.MovVector.size() &&
|
|
"Function call has more parameters than the stack is adjusted for.");
|
|
|
|
// If the same stack slot is being filled twice, something's fishy.
|
|
if (Context.MovVector[StackDisp] != nullptr)
|
|
return;
|
|
Context.MovVector[StackDisp] = I;
|
|
|
|
++I;
|
|
} while (I != MBB.end());
|
|
|
|
// We now expect the end of the sequence - a call and a stack adjust.
|
|
if (I == MBB.end())
|
|
return;
|
|
|
|
// For PCrel calls, we expect an additional COPY of the basereg.
|
|
// If we find one, skip it.
|
|
if (I->isCopy()) {
|
|
if (I->getOperand(1).getReg() ==
|
|
MF.getInfo<X86MachineFunctionInfo>()->getGlobalBaseReg())
|
|
++I;
|
|
else
|
|
return;
|
|
}
|
|
|
|
if (!I->isCall())
|
|
return;
|
|
|
|
Context.Call = I;
|
|
if ((++I)->getOpcode() != FrameDestroyOpcode)
|
|
return;
|
|
|
|
// Now, go through the vector, and see that we don't have any gaps,
|
|
// but only a series of 32-bit MOVs.
|
|
auto MMI = Context.MovVector.begin(), MME = Context.MovVector.end();
|
|
for (; MMI != MME; ++MMI, Context.ExpectedDist += 4)
|
|
if (*MMI == nullptr)
|
|
break;
|
|
|
|
// If the call had no parameters, do nothing
|
|
if (MMI == Context.MovVector.begin())
|
|
return;
|
|
|
|
// We are either at the last parameter, or a gap.
|
|
// Make sure it's not a gap
|
|
for (; MMI != MME; ++MMI)
|
|
if (*MMI != nullptr)
|
|
return;
|
|
|
|
Context.UsePush = true;
|
|
return;
|
|
}
|
|
|
|
bool X86CallFrameOptimization::adjustCallSequence(MachineFunction &MF,
|
|
MachineBasicBlock::iterator I,
|
|
const CallContext &Context) {
|
|
// Ok, we can in fact do the transformation for this call.
|
|
// Do not remove the FrameSetup instruction, but adjust the parameters.
|
|
// PEI will end up finalizing the handling of this.
|
|
MachineBasicBlock::iterator FrameSetup = I;
|
|
MachineBasicBlock &MBB = *(I->getParent());
|
|
FrameSetup->getOperand(1).setImm(Context.ExpectedDist);
|
|
|
|
DebugLoc DL = I->getDebugLoc();
|
|
// Now, iterate through the vector in reverse order, and replace the movs
|
|
// with pushes. MOVmi/MOVmr doesn't have any defs, so no need to
|
|
// replace uses.
|
|
for (int Idx = (Context.ExpectedDist / 4) - 1; Idx >= 0; --Idx) {
|
|
MachineBasicBlock::iterator MOV = *Context.MovVector[Idx];
|
|
MachineOperand PushOp = MOV->getOperand(X86::AddrNumOperands);
|
|
if (MOV->getOpcode() == X86::MOV32mi) {
|
|
unsigned PushOpcode = X86::PUSHi32;
|
|
// If the operand is a small (8-bit) immediate, we can use a
|
|
// PUSH instruction with a shorter encoding.
|
|
// Note that isImm() may fail even though this is a MOVmi, because
|
|
// the operand can also be a symbol.
|
|
if (PushOp.isImm()) {
|
|
int64_t Val = PushOp.getImm();
|
|
if (isInt<8>(Val))
|
|
PushOpcode = X86::PUSH32i8;
|
|
}
|
|
BuildMI(MBB, Context.Call, DL, TII->get(PushOpcode)).addOperand(PushOp);
|
|
} else {
|
|
unsigned int Reg = PushOp.getReg();
|
|
|
|
// If PUSHrmm is not slow on this target, try to fold the source of the
|
|
// push into the instruction.
|
|
const X86Subtarget &ST = MF.getSubtarget<X86Subtarget>();
|
|
bool SlowPUSHrmm = ST.isAtom() || ST.isSLM();
|
|
|
|
// Check that this is legal to fold. Right now, we're extremely
|
|
// conservative about that.
|
|
MachineInstr *DefMov = nullptr;
|
|
if (!SlowPUSHrmm && (DefMov = canFoldIntoRegPush(FrameSetup, Reg))) {
|
|
MachineInstr *Push =
|
|
BuildMI(MBB, Context.Call, DL, TII->get(X86::PUSH32rmm));
|
|
|
|
unsigned NumOps = DefMov->getDesc().getNumOperands();
|
|
for (unsigned i = NumOps - X86::AddrNumOperands; i != NumOps; ++i)
|
|
Push->addOperand(DefMov->getOperand(i));
|
|
|
|
DefMov->eraseFromParent();
|
|
} else {
|
|
BuildMI(MBB, Context.Call, DL, TII->get(X86::PUSH32r))
|
|
.addReg(Reg)
|
|
.getInstr();
|
|
}
|
|
}
|
|
|
|
MBB.erase(MOV);
|
|
}
|
|
|
|
// The stack-pointer copy is no longer used in the call sequences.
|
|
// There should not be any other users, but we can't commit to that, so:
|
|
if (MRI->use_empty(Context.SPCopy->getOperand(0).getReg()))
|
|
Context.SPCopy->eraseFromParent();
|
|
|
|
// Once we've done this, we need to make sure PEI doesn't assume a reserved
|
|
// frame.
|
|
X86MachineFunctionInfo *FuncInfo = MF.getInfo<X86MachineFunctionInfo>();
|
|
FuncInfo->setHasPushSequences(true);
|
|
|
|
return true;
|
|
}
|
|
|
|
MachineInstr *X86CallFrameOptimization::canFoldIntoRegPush(
|
|
MachineBasicBlock::iterator FrameSetup, unsigned Reg) {
|
|
// Do an extremely restricted form of load folding.
|
|
// ISel will often create patterns like:
|
|
// movl 4(%edi), %eax
|
|
// movl 8(%edi), %ecx
|
|
// movl 12(%edi), %edx
|
|
// movl %edx, 8(%esp)
|
|
// movl %ecx, 4(%esp)
|
|
// movl %eax, (%esp)
|
|
// call
|
|
// Get rid of those with prejudice.
|
|
if (!TargetRegisterInfo::isVirtualRegister(Reg))
|
|
return nullptr;
|
|
|
|
// Make sure this is the only use of Reg.
|
|
if (!MRI->hasOneNonDBGUse(Reg))
|
|
return nullptr;
|
|
|
|
MachineBasicBlock::iterator DefMI = MRI->getVRegDef(Reg);
|
|
|
|
// Make sure the def is a MOV from memory.
|
|
// If the def is an another block, give up.
|
|
if (DefMI->getOpcode() != X86::MOV32rm ||
|
|
DefMI->getParent() != FrameSetup->getParent())
|
|
return nullptr;
|
|
|
|
// Now, make sure everything else up until the ADJCALLSTACK is a sequence
|
|
// of MOVs. To be less conservative would require duplicating a lot of the
|
|
// logic from PeepholeOptimizer.
|
|
// FIXME: A possibly better approach would be to teach the PeepholeOptimizer
|
|
// to be smarter about folding into pushes.
|
|
for (auto I = DefMI; I != FrameSetup; ++I)
|
|
if (I->getOpcode() != X86::MOV32rm)
|
|
return nullptr;
|
|
|
|
return DefMI;
|
|
}
|