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[X86] Split information collection from actual transformation in call frame optimization

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This splits collecting information from actually performing the transformation, so that we can add a heuristic in between the two.
NFC.

Differential Revision: http://reviews.llvm.org/D7497

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228817 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Michael Kuperstein 2015-02-11 08:53:55 +00:00
parent 8ee1b65836
commit 0686b8affc
1 changed files with 101 additions and 60 deletions
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161
lib/Target/X86/X86CallFrameOptimization.cpp
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@ -8,7 +8,7 @@
//===----------------------------------------------------------------------===//
//
// This file defines a pass that optimizes call sequences on x86.
// Currently, it converts movs of function parameters onto the stack into
// 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
@ -52,15 +52,38 @@ public:
private:
bool shouldPerformTransformation(MachineFunction &MF);
bool adjustCallSequence(MachineFunction &MF, MachineBasicBlock &MBB,
MachineBasicBlock::iterator I);
// Information we know about a particular call site
struct CallContext {
CallContext()
: Call(nullptr), SPCopy(nullptr), ExpectedDist(0),
MovVector(4, nullptr), 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;
// Whether this site should use push instructions
bool UsePush;
};
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 char *getPassName() const override { return "X86 Optimize Call Frame"; }
const TargetInstrInfo *TII;
const TargetFrameLowering *TFL;
@ -76,7 +99,8 @@ FunctionPass *llvm::createX86CallFrameOptimization() {
}
// This checks whether the transformation is legal and profitable
bool X86CallFrameOptimization::shouldPerformTransformation(MachineFunction &MF) {
bool X86CallFrameOptimization::shouldPerformTransformation(
MachineFunction &MF) {
if (NoX86CFOpt.getValue())
return false;
@ -105,8 +129,7 @@ bool X86CallFrameOptimization::shouldPerformTransformation(MachineFunction &MF)
if (InsideFrameSequence)
return false;
InsideFrameSequence = true;
}
else if (MI.getOpcode() == FrameDestroyOpcode) {
} else if (MI.getOpcode() == FrameDestroyOpcode) {
if (!InsideFrameSequence)
return false;
InsideFrameSequence = false;
@ -123,7 +146,7 @@ bool X86CallFrameOptimization::shouldPerformTransformation(MachineFunction &MF)
// and enable this for more cases.
// This transformation is always a win when we expected to have
// a reserved call frame. Under other circumstances, it may be either
// a reserved call frame. Under other circumstances, it may be either
// a win or a loss, and requires a heuristic.
// For now, enable it only for the relatively clear win cases.
bool CannotReserveFrame = MF.getFrameInfo()->hasVarSizedObjects();
@ -134,9 +157,9 @@ bool X86CallFrameOptimization::shouldPerformTransformation(MachineFunction &MF)
// not optimizing for size.
AttributeSet FnAttrs = MF.getFunction()->getAttributes();
bool OptForSize =
FnAttrs.hasAttribute(AttributeSet::FunctionIndex,
Attribute::OptimizeForSize) ||
FnAttrs.hasAttribute(AttributeSet::FunctionIndex, Attribute::MinSize);
FnAttrs.hasAttribute(AttributeSet::FunctionIndex,
Attribute::OptimizeForSize) ||
FnAttrs.hasAttribute(AttributeSet::FunctionIndex, Attribute::MinSize);
if (!OptForSize)
return false;
@ -163,18 +186,26 @@ bool X86CallFrameOptimization::runOnMachineFunction(MachineFunction &MF) {
bool Changed = false;
DenseMap<MachineInstr *, CallContext> 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)
Changed |= adjustCallSequence(MF, *BB, I);
if (I->getOpcode() == FrameSetupOpcode) {
CallContext &Context = CallSeqMap[I];
collectCallInfo(MF, *BB, I, Context);
}
for (auto CC : CallSeqMap)
if (CC.second.UsePush)
Changed |= adjustCallSequence(MF, CC.first, CC.second);
return Changed;
}
bool X86CallFrameOptimization::adjustCallSequence(MachineFunction &MF,
MachineBasicBlock &MBB,
MachineBasicBlock::iterator I) {
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 *>(
@ -186,30 +217,28 @@ bool X86CallFrameOptimization::adjustCallSequence(MachineFunction &MF,
assert(I->getOpcode() == TII->getCallFrameSetupOpcode());
MachineBasicBlock::iterator FrameSetup = I++;
// 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 false;
MachineBasicBlock::iterator SPCopy = I++;
StackPtr = SPCopy->getOperand(0).getReg();
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.
SmallVector<MachineInstr*, 4> MovVector(4, nullptr);
unsigned int MaxAdjust = FrameSetup->getOperand(0).getImm() / 4;
if (MaxAdjust > 4)
MovVector.resize(MaxAdjust, nullptr);
Context.MovVector.resize(MaxAdjust, nullptr);
do {
int Opcode = I->getOpcode();
@ -231,77 +260,86 @@ bool X86CallFrameOptimization::adjustCallSequence(MachineFunction &MF,
(I->getOperand(X86::AddrIndexReg).getReg() != X86::NoRegister) ||
(I->getOperand(X86::AddrSegmentReg).getReg() != X86::NoRegister) ||
!I->getOperand(X86::AddrDisp).isImm())
return false;
return;
int64_t StackDisp = I->getOperand(X86::AddrDisp).getImm();
assert(StackDisp >= 0 && "Negative stack displacement when passing parameters");
assert(StackDisp >= 0 &&
"Negative stack displacement when passing parameters");
// We really don't want to consider the unaligned case.
if (StackDisp % 4)
return false;
return;
StackDisp /= 4;
assert((size_t)StackDisp < MovVector.size() &&
"Function call has more parameters than the stack is adjusted for.");
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 (MovVector[StackDisp] != nullptr)
return false;
MovVector[StackDisp] = I;
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 false;
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())
MF.getInfo<X86MachineFunctionInfo>()->getGlobalBaseReg())
++I;
else
return false;
return;
}
if (!I->isCall())
return false;
MachineBasicBlock::iterator Call = I;
return;
Context.Call = I;
if ((++I)->getOpcode() != FrameDestroyOpcode)
return false;
return;
// Now, go through the vector, and see that we don't have any gaps,
// but only a series of 32-bit MOVs.
int64_t ExpectedDist = 0;
auto MMI = MovVector.begin(), MME = MovVector.end();
for (; MMI != MME; ++MMI, ExpectedDist += 4)
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 (!ExpectedDist)
return false;
// We are either at the last parameter, or a gap.
// 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 false;
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.
FrameSetup->getOperand(1).setImm(ExpectedDist);
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
// with pushes. MOVmi/MOVmr doesn't have any defs, so no need to
// replace uses.
for (int Idx = (ExpectedDist / 4) - 1; Idx >= 0; --Idx) {
MachineBasicBlock::iterator MOV = *MovVector[Idx];
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;
@ -314,7 +352,7 @@ bool X86CallFrameOptimization::adjustCallSequence(MachineFunction &MF,
if (isInt<8>(Val))
PushOpcode = X86::PUSH32i8;
}
BuildMI(MBB, Call, DL, TII->get(PushOpcode)).addOperand(PushOp);
BuildMI(MBB, Context.Call, DL, TII->get(PushOpcode)).addOperand(PushOp);
} else {
unsigned int Reg = PushOp.getReg();
@ -327,7 +365,8 @@ bool X86CallFrameOptimization::adjustCallSequence(MachineFunction &MF,
// conservative about that.
MachineInstr *DefMov = nullptr;
if (!SlowPUSHrmm && (DefMov = canFoldIntoRegPush(FrameSetup, Reg))) {
MachineInstr *Push = BuildMI(MBB, Call, DL, TII->get(X86::PUSH32rmm));
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)
@ -335,7 +374,9 @@ bool X86CallFrameOptimization::adjustCallSequence(MachineFunction &MF,
DefMov->eraseFromParent();
} else {
BuildMI(MBB, Call, DL, TII->get(X86::PUSH32r)).addReg(Reg).getInstr();
BuildMI(MBB, Context.Call, DL, TII->get(X86::PUSH32r))
.addReg(Reg)
.getInstr();
}
}
@ -344,8 +385,8 @@ bool X86CallFrameOptimization::adjustCallSequence(MachineFunction &MF,
// 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(SPCopy->getOperand(0).getReg()))
SPCopy->eraseFromParent();
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.
@ -392,7 +433,7 @@ MachineInstr *X86CallFrameOptimization::canFoldIntoRegPush(
// 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.
// to be smarter about folding into pushes.
for (auto I = DefMI; I != FrameSetup; ++I)
if (I->getOpcode() != X86::MOV32rm)
return nullptr;