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llvm-mirror/lib/Target/X86/X86FloatingPoint.cpp
Jakob Stoklund Olesen 85931574b0 Don't clobber pending ST regs when FP regs are killed. 
X86FloatingPoint keeps track of pending ST registers for an upcoming
inline asm instruction with fixed stack register constraints.  It does
this by remembering which FP register holds the value that should appear
at a fixed stack position for the inline asm.

When that FP register is killed before the inline asm, make sure to
duplicate it to a scratch register, so the ST register still has a live
FP reference.

This could happen when the same FP register was copied to two ST
registers, or when a spill instruction is inserted between the ST copy
and the inline asm.

This fixes PR10602.

llvm-svn: 137050
2011-08-08 17:15:43 +00:00

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//===-- X86FloatingPoint.cpp - Floating point Reg -> Stack converter ------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the pass which converts floating point instructions from
// pseudo registers into register stack instructions. This pass uses live
// variable information to indicate where the FPn registers are used and their
// lifetimes.
//
// The x87 hardware tracks liveness of the stack registers, so it is necessary
// to implement exact liveness tracking between basic blocks. The CFG edges are
// partitioned into bundles where the same FP registers must be live in
// identical stack positions. Instructions are inserted at the end of each basic
// block to rearrange the live registers to match the outgoing bundle.
//
// This approach avoids splitting critical edges at the potential cost of more
// live register shuffling instructions when critical edges are present.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "x86-codegen"
#include "X86.h"
#include "X86InstrInfo.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/EdgeBundles.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/InlineAsm.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include <algorithm>
using namespace llvm;
STATISTIC(NumFXCH, "Number of fxch instructions inserted");
STATISTIC(NumFP , "Number of floating point instructions");
namespace {
struct FPS : public MachineFunctionPass {
static char ID;
FPS() : MachineFunctionPass(ID) {
initializeEdgeBundlesPass(*PassRegistry::getPassRegistry());
// This is really only to keep valgrind quiet.
// The logic in isLive() is too much for it.
memset(Stack, 0, sizeof(Stack));
memset(RegMap, 0, sizeof(RegMap));
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
AU.addRequired<EdgeBundles>();
AU.addPreservedID(MachineLoopInfoID);
AU.addPreservedID(MachineDominatorsID);
MachineFunctionPass::getAnalysisUsage(AU);
}
virtual bool runOnMachineFunction(MachineFunction &MF);
virtual const char *getPassName() const { return "X86 FP Stackifier"; }
private:
const TargetInstrInfo *TII; // Machine instruction info.
// Two CFG edges are related if they leave the same block, or enter the same
// block. The transitive closure of an edge under this relation is a
// LiveBundle. It represents a set of CFG edges where the live FP stack
// registers must be allocated identically in the x87 stack.
//
// A LiveBundle is usually all the edges leaving a block, or all the edges
// entering a block, but it can contain more edges if critical edges are
// present.
//
// The set of live FP registers in a LiveBundle is calculated by bundleCFG,
// but the exact mapping of FP registers to stack slots is fixed later.
struct LiveBundle {
// Bit mask of live FP registers. Bit 0 = FP0, bit 1 = FP1, &c.
unsigned Mask;
// Number of pre-assigned live registers in FixStack. This is 0 when the
// stack order has not yet been fixed.
unsigned FixCount;
// Assigned stack order for live-in registers.
// FixStack[i] == getStackEntry(i) for all i < FixCount.
unsigned char FixStack[8];
LiveBundle() : Mask(0), FixCount(0) {}
// Have the live registers been assigned a stack order yet?
bool isFixed() const { return !Mask || FixCount; }
};
// Numbered LiveBundle structs. LiveBundles[0] is used for all CFG edges
// with no live FP registers.
SmallVector<LiveBundle, 8> LiveBundles;
// The edge bundle analysis provides indices into the LiveBundles vector.
EdgeBundles *Bundles;
// Return a bitmask of FP registers in block's live-in list.
unsigned calcLiveInMask(MachineBasicBlock *MBB) {
unsigned Mask = 0;
for (MachineBasicBlock::livein_iterator I = MBB->livein_begin(),
E = MBB->livein_end(); I != E; ++I) {
unsigned Reg = *I - X86::FP0;
if (Reg < 8)
Mask |= 1 << Reg;
}
return Mask;
}
// Partition all the CFG edges into LiveBundles.
void bundleCFG(MachineFunction &MF);
MachineBasicBlock *MBB; // Current basic block
// The hardware keeps track of how many FP registers are live, so we have
// to model that exactly. Usually, each live register corresponds to an
// FP<n> register, but when dealing with calls, returns, and inline
// assembly, it is sometimes neccesary to have live scratch registers.
unsigned Stack[8]; // FP<n> Registers in each stack slot...
unsigned StackTop; // The current top of the FP stack.
enum {
NumFPRegs = 16 // Including scratch pseudo-registers.
};
// For each live FP<n> register, point to its Stack[] entry.
// The first entries correspond to FP0-FP6, the rest are scratch registers
// used when we need slightly different live registers than what the
// register allocator thinks.
unsigned RegMap[NumFPRegs];
// Pending fixed registers - Inline assembly needs FP registers to appear
// in fixed stack slot positions. This is handled by copying FP registers
// to ST registers before the instruction, and copying back after the
// instruction.
//
// This is modeled with pending ST registers. NumPendingSTs is the number
// of ST registers (ST0-STn) we are tracking. PendingST[n] points to an FP
// register that holds the ST value. The ST registers are not moved into
// place until immediately before the instruction that needs them.
//
// It can happen that we need an ST register to be live when no FP register
// holds the value:
//
// %ST0 = COPY %FP4<kill>
//
// When that happens, we allocate a scratch FP register to hold the ST
// value. That means every register in PendingST must be live.
unsigned NumPendingSTs;
unsigned char PendingST[8];
// Set up our stack model to match the incoming registers to MBB.
void setupBlockStack();
// Shuffle live registers to match the expectations of successor blocks.
void finishBlockStack();
void dumpStack() const {
dbgs() << "Stack contents:";
for (unsigned i = 0; i != StackTop; ++i) {
dbgs() << " FP" << Stack[i];
assert(RegMap[Stack[i]] == i && "Stack[] doesn't match RegMap[]!");
}
for (unsigned i = 0; i != NumPendingSTs; ++i)
dbgs() << ", ST" << i << " in FP" << unsigned(PendingST[i]);
dbgs() << "\n";
}
/// getSlot - Return the stack slot number a particular register number is
/// in.
unsigned getSlot(unsigned RegNo) const {
assert(RegNo < NumFPRegs && "Regno out of range!");
return RegMap[RegNo];
}
/// isLive - Is RegNo currently live in the stack?
bool isLive(unsigned RegNo) const {
unsigned Slot = getSlot(RegNo);
return Slot < StackTop && Stack[Slot] == RegNo;
}
/// getScratchReg - Return an FP register that is not currently in use.
unsigned getScratchReg() {
for (int i = NumFPRegs - 1; i >= 8; --i)
if (!isLive(i))
return i;
llvm_unreachable("Ran out of scratch FP registers");
}
/// isScratchReg - Returns trus if RegNo is a scratch FP register.
bool isScratchReg(unsigned RegNo) {
return RegNo > 8 && RegNo < NumFPRegs;
}
/// getStackEntry - Return the X86::FP<n> register in register ST(i).
unsigned getStackEntry(unsigned STi) const {
if (STi >= StackTop)
report_fatal_error("Access past stack top!");
return Stack[StackTop-1-STi];
}
/// getSTReg - Return the X86::ST(i) register which contains the specified
/// FP<RegNo> register.
unsigned getSTReg(unsigned RegNo) const {
return StackTop - 1 - getSlot(RegNo) + llvm::X86::ST0;
}
// pushReg - Push the specified FP<n> register onto the stack.
void pushReg(unsigned Reg) {
assert(Reg < NumFPRegs && "Register number out of range!");
if (StackTop >= 8)
report_fatal_error("Stack overflow!");
Stack[StackTop] = Reg;
RegMap[Reg] = StackTop++;
}
bool isAtTop(unsigned RegNo) const { return getSlot(RegNo) == StackTop-1; }
void moveToTop(unsigned RegNo, MachineBasicBlock::iterator I) {
DebugLoc dl = I == MBB->end() ? DebugLoc() : I->getDebugLoc();
if (isAtTop(RegNo)) return;
unsigned STReg = getSTReg(RegNo);
unsigned RegOnTop = getStackEntry(0);
// Swap the slots the regs are in.
std::swap(RegMap[RegNo], RegMap[RegOnTop]);
// Swap stack slot contents.
if (RegMap[RegOnTop] >= StackTop)
report_fatal_error("Access past stack top!");
std::swap(Stack[RegMap[RegOnTop]], Stack[StackTop-1]);
// Emit an fxch to update the runtime processors version of the state.
BuildMI(*MBB, I, dl, TII->get(X86::XCH_F)).addReg(STReg);
++NumFXCH;
}
void duplicateToTop(unsigned RegNo, unsigned AsReg, MachineInstr *I) {
DebugLoc dl = I == MBB->end() ? DebugLoc() : I->getDebugLoc();
unsigned STReg = getSTReg(RegNo);
pushReg(AsReg); // New register on top of stack
BuildMI(*MBB, I, dl, TII->get(X86::LD_Frr)).addReg(STReg);
}
/// duplicatePendingSTBeforeKill - The instruction at I is about to kill
/// RegNo. If any PendingST registers still need the RegNo value, duplicate
/// them to new scratch registers.
void duplicatePendingSTBeforeKill(unsigned RegNo, MachineInstr *I) {
for (unsigned i = 0; i != NumPendingSTs; ++i) {
if (PendingST[i] != RegNo)
continue;
unsigned SR = getScratchReg();
DEBUG(dbgs() << "Duplicating pending ST" << i
<< " in FP" << RegNo << " to FP" << SR << '\n');
duplicateToTop(RegNo, SR, I);
PendingST[i] = SR;
}
}
/// popStackAfter - Pop the current value off of the top of the FP stack
/// after the specified instruction.
void popStackAfter(MachineBasicBlock::iterator &I);
/// freeStackSlotAfter - Free the specified register from the register
/// stack, so that it is no longer in a register. If the register is
/// currently at the top of the stack, we just pop the current instruction,
/// otherwise we store the current top-of-stack into the specified slot,
/// then pop the top of stack.
void freeStackSlotAfter(MachineBasicBlock::iterator &I, unsigned Reg);
/// freeStackSlotBefore - Just the pop, no folding. Return the inserted
/// instruction.
MachineBasicBlock::iterator
freeStackSlotBefore(MachineBasicBlock::iterator I, unsigned FPRegNo);
/// Adjust the live registers to be the set in Mask.
void adjustLiveRegs(unsigned Mask, MachineBasicBlock::iterator I);
/// Shuffle the top FixCount stack entries such that FP reg FixStack[0] is
/// st(0), FP reg FixStack[1] is st(1) etc.
void shuffleStackTop(const unsigned char *FixStack, unsigned FixCount,
MachineBasicBlock::iterator I);
bool processBasicBlock(MachineFunction &MF, MachineBasicBlock &MBB);
void handleZeroArgFP(MachineBasicBlock::iterator &I);
void handleOneArgFP(MachineBasicBlock::iterator &I);
void handleOneArgFPRW(MachineBasicBlock::iterator &I);
void handleTwoArgFP(MachineBasicBlock::iterator &I);
void handleCompareFP(MachineBasicBlock::iterator &I);
void handleCondMovFP(MachineBasicBlock::iterator &I);
void handleSpecialFP(MachineBasicBlock::iterator &I);
// Check if a COPY instruction is using FP registers.
bool isFPCopy(MachineInstr *MI) {
unsigned DstReg = MI->getOperand(0).getReg();
unsigned SrcReg = MI->getOperand(1).getReg();
return X86::RFP80RegClass.contains(DstReg) ||
X86::RFP80RegClass.contains(SrcReg);
}
};
char FPS::ID = 0;
}
FunctionPass *llvm::createX86FloatingPointStackifierPass() { return new FPS(); }
/// getFPReg - Return the X86::FPx register number for the specified operand.
/// For example, this returns 3 for X86::FP3.
static unsigned getFPReg(const MachineOperand &MO) {
assert(MO.isReg() && "Expected an FP register!");
unsigned Reg = MO.getReg();
assert(Reg >= X86::FP0 && Reg <= X86::FP6 && "Expected FP register!");
return Reg - X86::FP0;
}
/// runOnMachineFunction - Loop over all of the basic blocks, transforming FP
/// register references into FP stack references.
///
bool FPS::runOnMachineFunction(MachineFunction &MF) {
// We only need to run this pass if there are any FP registers used in this
// function. If it is all integer, there is nothing for us to do!
bool FPIsUsed = false;
assert(X86::FP6 == X86::FP0+6 && "Register enums aren't sorted right!");
for (unsigned i = 0; i <= 6; ++i)
if (MF.getRegInfo().isPhysRegUsed(X86::FP0+i)) {
FPIsUsed = true;
break;
}
// Early exit.
if (!FPIsUsed) return false;
Bundles = &getAnalysis<EdgeBundles>();
TII = MF.getTarget().getInstrInfo();
// Prepare cross-MBB liveness.
bundleCFG(MF);
StackTop = 0;
// Process the function in depth first order so that we process at least one
// of the predecessors for every reachable block in the function.
SmallPtrSet<MachineBasicBlock*, 8> Processed;
MachineBasicBlock *Entry = MF.begin();
bool Changed = false;
for (df_ext_iterator<MachineBasicBlock*, SmallPtrSet<MachineBasicBlock*, 8> >
I = df_ext_begin(Entry, Processed), E = df_ext_end(Entry, Processed);
I != E; ++I)
Changed |= processBasicBlock(MF, **I);
// Process any unreachable blocks in arbitrary order now.
if (MF.size() != Processed.size())
for (MachineFunction::iterator BB = MF.begin(), E = MF.end(); BB != E; ++BB)
if (Processed.insert(BB))
Changed |= processBasicBlock(MF, *BB);
LiveBundles.clear();
return Changed;
}
/// bundleCFG - Scan all the basic blocks to determine consistent live-in and
/// live-out sets for the FP registers. Consistent means that the set of
/// registers live-out from a block is identical to the live-in set of all
/// successors. This is not enforced by the normal live-in lists since
/// registers may be implicitly defined, or not used by all successors.
void FPS::bundleCFG(MachineFunction &MF) {
assert(LiveBundles.empty() && "Stale data in LiveBundles");
LiveBundles.resize(Bundles->getNumBundles());
// Gather the actual live-in masks for all MBBs.
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
MachineBasicBlock *MBB = I;
const unsigned Mask = calcLiveInMask(MBB);
if (!Mask)
continue;
// Update MBB ingoing bundle mask.
LiveBundles[Bundles->getBundle(MBB->getNumber(), false)].Mask |= Mask;
}
}
/// processBasicBlock - Loop over all of the instructions in the basic block,
/// transforming FP instructions into their stack form.
///
bool FPS::processBasicBlock(MachineFunction &MF, MachineBasicBlock &BB) {
bool Changed = false;
MBB = &BB;
NumPendingSTs = 0;
setupBlockStack();
for (MachineBasicBlock::iterator I = BB.begin(); I != BB.end(); ++I) {
MachineInstr *MI = I;
uint64_t Flags = MI->getDesc().TSFlags;
unsigned FPInstClass = Flags & X86II::FPTypeMask;
if (MI->isInlineAsm())
FPInstClass = X86II::SpecialFP;
if (MI->isCopy() && isFPCopy(MI))
FPInstClass = X86II::SpecialFP;
if (MI->isImplicitDef() &&
X86::RFP80RegClass.contains(MI->getOperand(0).getReg()))
FPInstClass = X86II::SpecialFP;
if (FPInstClass == X86II::NotFP)
continue; // Efficiently ignore non-fp insts!
MachineInstr *PrevMI = 0;
if (I != BB.begin())
PrevMI = prior(I);
++NumFP; // Keep track of # of pseudo instrs
DEBUG(dbgs() << "\nFPInst:\t" << *MI);
// Get dead variables list now because the MI pointer may be deleted as part
// of processing!
SmallVector<unsigned, 8> DeadRegs;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
const MachineOperand &MO = MI->getOperand(i);
if (MO.isReg() && MO.isDead())
DeadRegs.push_back(MO.getReg());
}
switch (FPInstClass) {
case X86II::ZeroArgFP: handleZeroArgFP(I); break;
case X86II::OneArgFP: handleOneArgFP(I); break; // fstp ST(0)
case X86II::OneArgFPRW: handleOneArgFPRW(I); break; // ST(0) = fsqrt(ST(0))
case X86II::TwoArgFP: handleTwoArgFP(I); break;
case X86II::CompareFP: handleCompareFP(I); break;
case X86II::CondMovFP: handleCondMovFP(I); break;
case X86II::SpecialFP: handleSpecialFP(I); break;
default: llvm_unreachable("Unknown FP Type!");
}
// Check to see if any of the values defined by this instruction are dead
// after definition. If so, pop them.
for (unsigned i = 0, e = DeadRegs.size(); i != e; ++i) {
unsigned Reg = DeadRegs[i];
if (Reg >= X86::FP0 && Reg <= X86::FP6) {
DEBUG(dbgs() << "Register FP#" << Reg-X86::FP0 << " is dead!\n");
freeStackSlotAfter(I, Reg-X86::FP0);
}
}
// Print out all of the instructions expanded to if -debug
DEBUG(
MachineBasicBlock::iterator PrevI(PrevMI);
if (I == PrevI) {
dbgs() << "Just deleted pseudo instruction\n";
} else {
MachineBasicBlock::iterator Start = I;
// Rewind to first instruction newly inserted.
while (Start != BB.begin() && prior(Start) != PrevI) --Start;
dbgs() << "Inserted instructions:\n\t";
Start->print(dbgs(), &MF.getTarget());
while (++Start != llvm::next(I)) {}
}
dumpStack();
);
Changed = true;
}
finishBlockStack();
return Changed;
}
/// setupBlockStack - Use the live bundles to set up our model of the stack
/// to match predecessors' live out stack.
void FPS::setupBlockStack() {
DEBUG(dbgs() << "\nSetting up live-ins for BB#" << MBB->getNumber()
<< " derived from " << MBB->getName() << ".\n");
StackTop = 0;
// Get the live-in bundle for MBB.
const LiveBundle &Bundle =
LiveBundles[Bundles->getBundle(MBB->getNumber(), false)];
if (!Bundle.Mask) {
DEBUG(dbgs() << "Block has no FP live-ins.\n");
return;
}
// Depth-first iteration should ensure that we always have an assigned stack.
assert(Bundle.isFixed() && "Reached block before any predecessors");
// Push the fixed live-in registers.
for (unsigned i = Bundle.FixCount; i > 0; --i) {
MBB->addLiveIn(X86::ST0+i-1);
DEBUG(dbgs() << "Live-in st(" << (i-1) << "): %FP"
<< unsigned(Bundle.FixStack[i-1]) << '\n');
pushReg(Bundle.FixStack[i-1]);
}
// Kill off unwanted live-ins. This can happen with a critical edge.
// FIXME: We could keep these live registers around as zombies. They may need
// to be revived at the end of a short block. It might save a few instrs.
adjustLiveRegs(calcLiveInMask(MBB), MBB->begin());
DEBUG(MBB->dump());
}
/// finishBlockStack - Revive live-outs that are implicitly defined out of
/// MBB. Shuffle live registers to match the expected fixed stack of any
/// predecessors, and ensure that all predecessors are expecting the same
/// stack.
void FPS::finishBlockStack() {
// The RET handling below takes care of return blocks for us.
if (MBB->succ_empty())
return;
DEBUG(dbgs() << "Setting up live-outs for BB#" << MBB->getNumber()
<< " derived from " << MBB->getName() << ".\n");
// Get MBB's live-out bundle.
unsigned BundleIdx = Bundles->getBundle(MBB->getNumber(), true);
LiveBundle &Bundle = LiveBundles[BundleIdx];
// We may need to kill and define some registers to match successors.
// FIXME: This can probably be combined with the shuffle below.
MachineBasicBlock::iterator Term = MBB->getFirstTerminator();
adjustLiveRegs(Bundle.Mask, Term);
if (!Bundle.Mask) {
DEBUG(dbgs() << "No live-outs.\n");
return;
}
// Has the stack order been fixed yet?
DEBUG(dbgs() << "LB#" << BundleIdx << ": ");
if (Bundle.isFixed()) {
DEBUG(dbgs() << "Shuffling stack to match.\n");
shuffleStackTop(Bundle.FixStack, Bundle.FixCount, Term);
} else {
// Not fixed yet, we get to choose.
DEBUG(dbgs() << "Fixing stack order now.\n");
Bundle.FixCount = StackTop;
for (unsigned i = 0; i < StackTop; ++i)
Bundle.FixStack[i] = getStackEntry(i);
}
}
//===----------------------------------------------------------------------===//
// Efficient Lookup Table Support
//===----------------------------------------------------------------------===//
namespace {
struct TableEntry {
unsigned from;
unsigned to;
bool operator<(const TableEntry &TE) const { return from < TE.from; }
friend bool operator<(const TableEntry &TE, unsigned V) {
return TE.from < V;
}
friend bool LLVM_ATTRIBUTE_USED operator<(unsigned V,
const TableEntry &TE) {
return V < TE.from;
}
};
}
#ifndef NDEBUG
static bool TableIsSorted(const TableEntry *Table, unsigned NumEntries) {
for (unsigned i = 0; i != NumEntries-1; ++i)
if (!(Table[i] < Table[i+1])) return false;
return true;
}
#endif
static int Lookup(const TableEntry *Table, unsigned N, unsigned Opcode) {
const TableEntry *I = std::lower_bound(Table, Table+N, Opcode);
if (I != Table+N && I->from == Opcode)
return I->to;
return -1;
}
#ifdef NDEBUG
#define ASSERT_SORTED(TABLE)
#else
#define ASSERT_SORTED(TABLE) \
{ static bool TABLE##Checked = false; \
if (!TABLE##Checked) { \
assert(TableIsSorted(TABLE, array_lengthof(TABLE)) && \
"All lookup tables must be sorted for efficient access!"); \
TABLE##Checked = true; \
} \
}
#endif
//===----------------------------------------------------------------------===//
// Register File -> Register Stack Mapping Methods
//===----------------------------------------------------------------------===//
// OpcodeTable - Sorted map of register instructions to their stack version.
// The first element is an register file pseudo instruction, the second is the
// concrete X86 instruction which uses the register stack.
//
static const TableEntry OpcodeTable[] = {
{ X86::ABS_Fp32 , X86::ABS_F },
{ X86::ABS_Fp64 , X86::ABS_F },
{ X86::ABS_Fp80 , X86::ABS_F },
{ X86::ADD_Fp32m , X86::ADD_F32m },
{ X86::ADD_Fp64m , X86::ADD_F64m },
{ X86::ADD_Fp64m32 , X86::ADD_F32m },
{ X86::ADD_Fp80m32 , X86::ADD_F32m },
{ X86::ADD_Fp80m64 , X86::ADD_F64m },
{ X86::ADD_FpI16m32 , X86::ADD_FI16m },
{ X86::ADD_FpI16m64 , X86::ADD_FI16m },
{ X86::ADD_FpI16m80 , X86::ADD_FI16m },
{ X86::ADD_FpI32m32 , X86::ADD_FI32m },
{ X86::ADD_FpI32m64 , X86::ADD_FI32m },
{ X86::ADD_FpI32m80 , X86::ADD_FI32m },
{ X86::CHS_Fp32 , X86::CHS_F },
{ X86::CHS_Fp64 , X86::CHS_F },
{ X86::CHS_Fp80 , X86::CHS_F },
{ X86::CMOVBE_Fp32 , X86::CMOVBE_F },
{ X86::CMOVBE_Fp64 , X86::CMOVBE_F },
{ X86::CMOVBE_Fp80 , X86::CMOVBE_F },
{ X86::CMOVB_Fp32 , X86::CMOVB_F },
{ X86::CMOVB_Fp64 , X86::CMOVB_F },
{ X86::CMOVB_Fp80 , X86::CMOVB_F },
{ X86::CMOVE_Fp32 , X86::CMOVE_F },
{ X86::CMOVE_Fp64 , X86::CMOVE_F },
{ X86::CMOVE_Fp80 , X86::CMOVE_F },
{ X86::CMOVNBE_Fp32 , X86::CMOVNBE_F },
{ X86::CMOVNBE_Fp64 , X86::CMOVNBE_F },
{ X86::CMOVNBE_Fp80 , X86::CMOVNBE_F },
{ X86::CMOVNB_Fp32 , X86::CMOVNB_F },
{ X86::CMOVNB_Fp64 , X86::CMOVNB_F },
{ X86::CMOVNB_Fp80 , X86::CMOVNB_F },
{ X86::CMOVNE_Fp32 , X86::CMOVNE_F },
{ X86::CMOVNE_Fp64 , X86::CMOVNE_F },
{ X86::CMOVNE_Fp80 , X86::CMOVNE_F },
{ X86::CMOVNP_Fp32 , X86::CMOVNP_F },
{ X86::CMOVNP_Fp64 , X86::CMOVNP_F },
{ X86::CMOVNP_Fp80 , X86::CMOVNP_F },
{ X86::CMOVP_Fp32 , X86::CMOVP_F },
{ X86::CMOVP_Fp64 , X86::CMOVP_F },
{ X86::CMOVP_Fp80 , X86::CMOVP_F },
{ X86::COS_Fp32 , X86::COS_F },
{ X86::COS_Fp64 , X86::COS_F },
{ X86::COS_Fp80 , X86::COS_F },
{ X86::DIVR_Fp32m , X86::DIVR_F32m },
{ X86::DIVR_Fp64m , X86::DIVR_F64m },
{ X86::DIVR_Fp64m32 , X86::DIVR_F32m },
{ X86::DIVR_Fp80m32 , X86::DIVR_F32m },
{ X86::DIVR_Fp80m64 , X86::DIVR_F64m },
{ X86::DIVR_FpI16m32, X86::DIVR_FI16m},
{ X86::DIVR_FpI16m64, X86::DIVR_FI16m},
{ X86::DIVR_FpI16m80, X86::DIVR_FI16m},
{ X86::DIVR_FpI32m32, X86::DIVR_FI32m},
{ X86::DIVR_FpI32m64, X86::DIVR_FI32m},
{ X86::DIVR_FpI32m80, X86::DIVR_FI32m},
{ X86::DIV_Fp32m , X86::DIV_F32m },
{ X86::DIV_Fp64m , X86::DIV_F64m },
{ X86::DIV_Fp64m32 , X86::DIV_F32m },
{ X86::DIV_Fp80m32 , X86::DIV_F32m },
{ X86::DIV_Fp80m64 , X86::DIV_F64m },
{ X86::DIV_FpI16m32 , X86::DIV_FI16m },
{ X86::DIV_FpI16m64 , X86::DIV_FI16m },
{ X86::DIV_FpI16m80 , X86::DIV_FI16m },
{ X86::DIV_FpI32m32 , X86::DIV_FI32m },
{ X86::DIV_FpI32m64 , X86::DIV_FI32m },
{ X86::DIV_FpI32m80 , X86::DIV_FI32m },
{ X86::ILD_Fp16m32 , X86::ILD_F16m },
{ X86::ILD_Fp16m64 , X86::ILD_F16m },
{ X86::ILD_Fp16m80 , X86::ILD_F16m },
{ X86::ILD_Fp32m32 , X86::ILD_F32m },
{ X86::ILD_Fp32m64 , X86::ILD_F32m },
{ X86::ILD_Fp32m80 , X86::ILD_F32m },
{ X86::ILD_Fp64m32 , X86::ILD_F64m },
{ X86::ILD_Fp64m64 , X86::ILD_F64m },
{ X86::ILD_Fp64m80 , X86::ILD_F64m },
{ X86::ISTT_Fp16m32 , X86::ISTT_FP16m},
{ X86::ISTT_Fp16m64 , X86::ISTT_FP16m},
{ X86::ISTT_Fp16m80 , X86::ISTT_FP16m},
{ X86::ISTT_Fp32m32 , X86::ISTT_FP32m},
{ X86::ISTT_Fp32m64 , X86::ISTT_FP32m},
{ X86::ISTT_Fp32m80 , X86::ISTT_FP32m},
{ X86::ISTT_Fp64m32 , X86::ISTT_FP64m},
{ X86::ISTT_Fp64m64 , X86::ISTT_FP64m},
{ X86::ISTT_Fp64m80 , X86::ISTT_FP64m},
{ X86::IST_Fp16m32 , X86::IST_F16m },
{ X86::IST_Fp16m64 , X86::IST_F16m },
{ X86::IST_Fp16m80 , X86::IST_F16m },
{ X86::IST_Fp32m32 , X86::IST_F32m },
{ X86::IST_Fp32m64 , X86::IST_F32m },
{ X86::IST_Fp32m80 , X86::IST_F32m },
{ X86::IST_Fp64m32 , X86::IST_FP64m },
{ X86::IST_Fp64m64 , X86::IST_FP64m },
{ X86::IST_Fp64m80 , X86::IST_FP64m },
{ X86::LD_Fp032 , X86::LD_F0 },
{ X86::LD_Fp064 , X86::LD_F0 },
{ X86::LD_Fp080 , X86::LD_F0 },
{ X86::LD_Fp132 , X86::LD_F1 },
{ X86::LD_Fp164 , X86::LD_F1 },
{ X86::LD_Fp180 , X86::LD_F1 },
{ X86::LD_Fp32m , X86::LD_F32m },
{ X86::LD_Fp32m64 , X86::LD_F32m },
{ X86::LD_Fp32m80 , X86::LD_F32m },
{ X86::LD_Fp64m , X86::LD_F64m },
{ X86::LD_Fp64m80 , X86::LD_F64m },
{ X86::LD_Fp80m , X86::LD_F80m },
{ X86::MUL_Fp32m , X86::MUL_F32m },
{ X86::MUL_Fp64m , X86::MUL_F64m },
{ X86::MUL_Fp64m32 , X86::MUL_F32m },
{ X86::MUL_Fp80m32 , X86::MUL_F32m },
{ X86::MUL_Fp80m64 , X86::MUL_F64m },
{ X86::MUL_FpI16m32 , X86::MUL_FI16m },
{ X86::MUL_FpI16m64 , X86::MUL_FI16m },
{ X86::MUL_FpI16m80 , X86::MUL_FI16m },
{ X86::MUL_FpI32m32 , X86::MUL_FI32m },
{ X86::MUL_FpI32m64 , X86::MUL_FI32m },
{ X86::MUL_FpI32m80 , X86::MUL_FI32m },
{ X86::SIN_Fp32 , X86::SIN_F },
{ X86::SIN_Fp64 , X86::SIN_F },
{ X86::SIN_Fp80 , X86::SIN_F },
{ X86::SQRT_Fp32 , X86::SQRT_F },
{ X86::SQRT_Fp64 , X86::SQRT_F },
{ X86::SQRT_Fp80 , X86::SQRT_F },
{ X86::ST_Fp32m , X86::ST_F32m },
{ X86::ST_Fp64m , X86::ST_F64m },
{ X86::ST_Fp64m32 , X86::ST_F32m },
{ X86::ST_Fp80m32 , X86::ST_F32m },
{ X86::ST_Fp80m64 , X86::ST_F64m },
{ X86::ST_FpP80m , X86::ST_FP80m },
{ X86::SUBR_Fp32m , X86::SUBR_F32m },
{ X86::SUBR_Fp64m , X86::SUBR_F64m },
{ X86::SUBR_Fp64m32 , X86::SUBR_F32m },
{ X86::SUBR_Fp80m32 , X86::SUBR_F32m },
{ X86::SUBR_Fp80m64 , X86::SUBR_F64m },
{ X86::SUBR_FpI16m32, X86::SUBR_FI16m},
{ X86::SUBR_FpI16m64, X86::SUBR_FI16m},
{ X86::SUBR_FpI16m80, X86::SUBR_FI16m},
{ X86::SUBR_FpI32m32, X86::SUBR_FI32m},
{ X86::SUBR_FpI32m64, X86::SUBR_FI32m},
{ X86::SUBR_FpI32m80, X86::SUBR_FI32m},
{ X86::SUB_Fp32m , X86::SUB_F32m },
{ X86::SUB_Fp64m , X86::SUB_F64m },
{ X86::SUB_Fp64m32 , X86::SUB_F32m },
{ X86::SUB_Fp80m32 , X86::SUB_F32m },
{ X86::SUB_Fp80m64 , X86::SUB_F64m },
{ X86::SUB_FpI16m32 , X86::SUB_FI16m },
{ X86::SUB_FpI16m64 , X86::SUB_FI16m },
{ X86::SUB_FpI16m80 , X86::SUB_FI16m },
{ X86::SUB_FpI32m32 , X86::SUB_FI32m },
{ X86::SUB_FpI32m64 , X86::SUB_FI32m },
{ X86::SUB_FpI32m80 , X86::SUB_FI32m },
{ X86::TST_Fp32 , X86::TST_F },
{ X86::TST_Fp64 , X86::TST_F },
{ X86::TST_Fp80 , X86::TST_F },
{ X86::UCOM_FpIr32 , X86::UCOM_FIr },
{ X86::UCOM_FpIr64 , X86::UCOM_FIr },
{ X86::UCOM_FpIr80 , X86::UCOM_FIr },
{ X86::UCOM_Fpr32 , X86::UCOM_Fr },
{ X86::UCOM_Fpr64 , X86::UCOM_Fr },
{ X86::UCOM_Fpr80 , X86::UCOM_Fr },
};
static unsigned getConcreteOpcode(unsigned Opcode) {
ASSERT_SORTED(OpcodeTable);
int Opc = Lookup(OpcodeTable, array_lengthof(OpcodeTable), Opcode);
assert(Opc != -1 && "FP Stack instruction not in OpcodeTable!");
return Opc;
}
//===----------------------------------------------------------------------===//
// Helper Methods
//===----------------------------------------------------------------------===//
// PopTable - Sorted map of instructions to their popping version. The first
// element is an instruction, the second is the version which pops.
//
static const TableEntry PopTable[] = {
{ X86::ADD_FrST0 , X86::ADD_FPrST0 },
{ X86::DIVR_FrST0, X86::DIVR_FPrST0 },
{ X86::DIV_FrST0 , X86::DIV_FPrST0 },
{ X86::IST_F16m , X86::IST_FP16m },
{ X86::IST_F32m , X86::IST_FP32m },
{ X86::MUL_FrST0 , X86::MUL_FPrST0 },
{ X86::ST_F32m , X86::ST_FP32m },
{ X86::ST_F64m , X86::ST_FP64m },
{ X86::ST_Frr , X86::ST_FPrr },
{ X86::SUBR_FrST0, X86::SUBR_FPrST0 },
{ X86::SUB_FrST0 , X86::SUB_FPrST0 },
{ X86::UCOM_FIr , X86::UCOM_FIPr },
{ X86::UCOM_FPr , X86::UCOM_FPPr },
{ X86::UCOM_Fr , X86::UCOM_FPr },
};
/// popStackAfter - Pop the current value off of the top of the FP stack after
/// the specified instruction. This attempts to be sneaky and combine the pop
/// into the instruction itself if possible. The iterator is left pointing to
/// the last instruction, be it a new pop instruction inserted, or the old
/// instruction if it was modified in place.
///
void FPS::popStackAfter(MachineBasicBlock::iterator &I) {
MachineInstr* MI = I;
DebugLoc dl = MI->getDebugLoc();
ASSERT_SORTED(PopTable);
if (StackTop == 0)
report_fatal_error("Cannot pop empty stack!");
RegMap[Stack[--StackTop]] = ~0; // Update state
// Check to see if there is a popping version of this instruction...
int Opcode = Lookup(PopTable, array_lengthof(PopTable), I->getOpcode());
if (Opcode != -1) {
I->setDesc(TII->get(Opcode));
if (Opcode == X86::UCOM_FPPr)
I->RemoveOperand(0);
} else { // Insert an explicit pop
I = BuildMI(*MBB, ++I, dl, TII->get(X86::ST_FPrr)).addReg(X86::ST0);
}
}
/// freeStackSlotAfter - Free the specified register from the register stack, so
/// that it is no longer in a register. If the register is currently at the top
/// of the stack, we just pop the current instruction, otherwise we store the
/// current top-of-stack into the specified slot, then pop the top of stack.
void FPS::freeStackSlotAfter(MachineBasicBlock::iterator &I, unsigned FPRegNo) {
if (getStackEntry(0) == FPRegNo) { // already at the top of stack? easy.
popStackAfter(I);
return;
}
// Otherwise, store the top of stack into the dead slot, killing the operand
// without having to add in an explicit xchg then pop.
//
I = freeStackSlotBefore(++I, FPRegNo);
}
/// freeStackSlotBefore - Free the specified register without trying any
/// folding.
MachineBasicBlock::iterator
FPS::freeStackSlotBefore(MachineBasicBlock::iterator I, unsigned FPRegNo) {
unsigned STReg = getSTReg(FPRegNo);
unsigned OldSlot = getSlot(FPRegNo);
unsigned TopReg = Stack[StackTop-1];
Stack[OldSlot] = TopReg;
RegMap[TopReg] = OldSlot;
RegMap[FPRegNo] = ~0;
Stack[--StackTop] = ~0;
return BuildMI(*MBB, I, DebugLoc(), TII->get(X86::ST_FPrr)).addReg(STReg);
}
/// adjustLiveRegs - Kill and revive registers such that exactly the FP
/// registers with a bit in Mask are live.
void FPS::adjustLiveRegs(unsigned Mask, MachineBasicBlock::iterator I) {
unsigned Defs = Mask;
unsigned Kills = 0;
for (unsigned i = 0; i < StackTop; ++i) {
unsigned RegNo = Stack[i];
if (!(Defs & (1 << RegNo)))
// This register is live, but we don't want it.
Kills |= (1 << RegNo);
else
// We don't need to imp-def this live register.
Defs &= ~(1 << RegNo);
}
assert((Kills & Defs) == 0 && "Register needs killing and def'ing?");
// Produce implicit-defs for free by using killed registers.
while (Kills && Defs) {
unsigned KReg = CountTrailingZeros_32(Kills);
unsigned DReg = CountTrailingZeros_32(Defs);
DEBUG(dbgs() << "Renaming %FP" << KReg << " as imp %FP" << DReg << "\n");
std::swap(Stack[getSlot(KReg)], Stack[getSlot(DReg)]);
std::swap(RegMap[KReg], RegMap[DReg]);
Kills &= ~(1 << KReg);
Defs &= ~(1 << DReg);
}
// Kill registers by popping.
if (Kills && I != MBB->begin()) {
MachineBasicBlock::iterator I2 = llvm::prior(I);
while (StackTop) {
unsigned KReg = getStackEntry(0);
if (!(Kills & (1 << KReg)))
break;
DEBUG(dbgs() << "Popping %FP" << KReg << "\n");
popStackAfter(I2);
Kills &= ~(1 << KReg);
}
}
// Manually kill the rest.
while (Kills) {
unsigned KReg = CountTrailingZeros_32(Kills);
DEBUG(dbgs() << "Killing %FP" << KReg << "\n");
freeStackSlotBefore(I, KReg);
Kills &= ~(1 << KReg);
}
// Load zeros for all the imp-defs.
while(Defs) {
unsigned DReg = CountTrailingZeros_32(Defs);
DEBUG(dbgs() << "Defining %FP" << DReg << " as 0\n");
BuildMI(*MBB, I, DebugLoc(), TII->get(X86::LD_F0));
pushReg(DReg);
Defs &= ~(1 << DReg);
}
// Now we should have the correct registers live.
DEBUG(dumpStack());
assert(StackTop == CountPopulation_32(Mask) && "Live count mismatch");
}
/// shuffleStackTop - emit fxch instructions before I to shuffle the top
/// FixCount entries into the order given by FixStack.
/// FIXME: Is there a better algorithm than insertion sort?
void FPS::shuffleStackTop(const unsigned char *FixStack,
unsigned FixCount,
MachineBasicBlock::iterator I) {
// Move items into place, starting from the desired stack bottom.
while (FixCount--) {
// Old register at position FixCount.
unsigned OldReg = getStackEntry(FixCount);
// Desired register at position FixCount.
unsigned Reg = FixStack[FixCount];
if (Reg == OldReg)
continue;
// (Reg st0) (OldReg st0) = (Reg OldReg st0)
moveToTop(Reg, I);
if (FixCount > 0)
moveToTop(OldReg, I);
}
DEBUG(dumpStack());
}
//===----------------------------------------------------------------------===//
// Instruction transformation implementation
//===----------------------------------------------------------------------===//
/// handleZeroArgFP - ST(0) = fld0 ST(0) = flds <mem>
///
void FPS::handleZeroArgFP(MachineBasicBlock::iterator &I) {
MachineInstr *MI = I;
unsigned DestReg = getFPReg(MI->getOperand(0));
// Change from the pseudo instruction to the concrete instruction.
MI->RemoveOperand(0); // Remove the explicit ST(0) operand
MI->setDesc(TII->get(getConcreteOpcode(MI->getOpcode())));
// Result gets pushed on the stack.
pushReg(DestReg);
}
/// handleOneArgFP - fst <mem>, ST(0)
///
void FPS::handleOneArgFP(MachineBasicBlock::iterator &I) {
MachineInstr *MI = I;
unsigned NumOps = MI->getDesc().getNumOperands();
assert((NumOps == X86::AddrNumOperands + 1 || NumOps == 1) &&
"Can only handle fst* & ftst instructions!");
// Is this the last use of the source register?
unsigned Reg = getFPReg(MI->getOperand(NumOps-1));
bool KillsSrc = MI->killsRegister(X86::FP0+Reg);
if (KillsSrc)
duplicatePendingSTBeforeKill(Reg, I);
// FISTP64m is strange because there isn't a non-popping versions.
// If we have one _and_ we don't want to pop the operand, duplicate the value
// on the stack instead of moving it. This ensure that popping the value is
// always ok.
// Ditto FISTTP16m, FISTTP32m, FISTTP64m, ST_FpP80m.
//
if (!KillsSrc &&
(MI->getOpcode() == X86::IST_Fp64m32 ||
MI->getOpcode() == X86::ISTT_Fp16m32 ||
MI->getOpcode() == X86::ISTT_Fp32m32 ||
MI->getOpcode() == X86::ISTT_Fp64m32 ||
MI->getOpcode() == X86::IST_Fp64m64 ||
MI->getOpcode() == X86::ISTT_Fp16m64 ||
MI->getOpcode() == X86::ISTT_Fp32m64 ||
MI->getOpcode() == X86::ISTT_Fp64m64 ||
MI->getOpcode() == X86::IST_Fp64m80 ||
MI->getOpcode() == X86::ISTT_Fp16m80 ||
MI->getOpcode() == X86::ISTT_Fp32m80 ||
MI->getOpcode() == X86::ISTT_Fp64m80 ||
MI->getOpcode() == X86::ST_FpP80m)) {
duplicateToTop(Reg, getScratchReg(), I);
} else {
moveToTop(Reg, I); // Move to the top of the stack...
}
// Convert from the pseudo instruction to the concrete instruction.
MI->RemoveOperand(NumOps-1); // Remove explicit ST(0) operand
MI->setDesc(TII->get(getConcreteOpcode(MI->getOpcode())));
if (MI->getOpcode() == X86::IST_FP64m ||
MI->getOpcode() == X86::ISTT_FP16m ||
MI->getOpcode() == X86::ISTT_FP32m ||
MI->getOpcode() == X86::ISTT_FP64m ||
MI->getOpcode() == X86::ST_FP80m) {
if (StackTop == 0)
report_fatal_error("Stack empty??");
--StackTop;
} else if (KillsSrc) { // Last use of operand?
popStackAfter(I);
}
}
/// handleOneArgFPRW: Handle instructions that read from the top of stack and
/// replace the value with a newly computed value. These instructions may have
/// non-fp operands after their FP operands.
///
/// Examples:
/// R1 = fchs R2
/// R1 = fadd R2, [mem]
///
void FPS::handleOneArgFPRW(MachineBasicBlock::iterator &I) {
MachineInstr *MI = I;
#ifndef NDEBUG
unsigned NumOps = MI->getDesc().getNumOperands();
assert(NumOps >= 2 && "FPRW instructions must have 2 ops!!");
#endif
// Is this the last use of the source register?
unsigned Reg = getFPReg(MI->getOperand(1));
bool KillsSrc = MI->killsRegister(X86::FP0+Reg);
if (KillsSrc) {
duplicatePendingSTBeforeKill(Reg, I);
// If this is the last use of the source register, just make sure it's on
// the top of the stack.
moveToTop(Reg, I);
if (StackTop == 0)
report_fatal_error("Stack cannot be empty!");
--StackTop;
pushReg(getFPReg(MI->getOperand(0)));
} else {
// If this is not the last use of the source register, _copy_ it to the top
// of the stack.
duplicateToTop(Reg, getFPReg(MI->getOperand(0)), I);
}
// Change from the pseudo instruction to the concrete instruction.
MI->RemoveOperand(1); // Drop the source operand.
MI->RemoveOperand(0); // Drop the destination operand.
MI->setDesc(TII->get(getConcreteOpcode(MI->getOpcode())));
}
//===----------------------------------------------------------------------===//
// Define tables of various ways to map pseudo instructions
//
// ForwardST0Table - Map: A = B op C into: ST(0) = ST(0) op ST(i)
static const TableEntry ForwardST0Table[] = {
{ X86::ADD_Fp32 , X86::ADD_FST0r },
{ X86::ADD_Fp64 , X86::ADD_FST0r },
{ X86::ADD_Fp80 , X86::ADD_FST0r },
{ X86::DIV_Fp32 , X86::DIV_FST0r },
{ X86::DIV_Fp64 , X86::DIV_FST0r },
{ X86::DIV_Fp80 , X86::DIV_FST0r },
{ X86::MUL_Fp32 , X86::MUL_FST0r },
{ X86::MUL_Fp64 , X86::MUL_FST0r },
{ X86::MUL_Fp80 , X86::MUL_FST0r },
{ X86::SUB_Fp32 , X86::SUB_FST0r },
{ X86::SUB_Fp64 , X86::SUB_FST0r },
{ X86::SUB_Fp80 , X86::SUB_FST0r },
};
// ReverseST0Table - Map: A = B op C into: ST(0) = ST(i) op ST(0)
static const TableEntry ReverseST0Table[] = {
{ X86::ADD_Fp32 , X86::ADD_FST0r }, // commutative
{ X86::ADD_Fp64 , X86::ADD_FST0r }, // commutative
{ X86::ADD_Fp80 , X86::ADD_FST0r }, // commutative
{ X86::DIV_Fp32 , X86::DIVR_FST0r },
{ X86::DIV_Fp64 , X86::DIVR_FST0r },
{ X86::DIV_Fp80 , X86::DIVR_FST0r },
{ X86::MUL_Fp32 , X86::MUL_FST0r }, // commutative
{ X86::MUL_Fp64 , X86::MUL_FST0r }, // commutative
{ X86::MUL_Fp80 , X86::MUL_FST0r }, // commutative
{ X86::SUB_Fp32 , X86::SUBR_FST0r },
{ X86::SUB_Fp64 , X86::SUBR_FST0r },
{ X86::SUB_Fp80 , X86::SUBR_FST0r },
};
// ForwardSTiTable - Map: A = B op C into: ST(i) = ST(0) op ST(i)
static const TableEntry ForwardSTiTable[] = {
{ X86::ADD_Fp32 , X86::ADD_FrST0 }, // commutative
{ X86::ADD_Fp64 , X86::ADD_FrST0 }, // commutative
{ X86::ADD_Fp80 , X86::ADD_FrST0 }, // commutative
{ X86::DIV_Fp32 , X86::DIVR_FrST0 },
{ X86::DIV_Fp64 , X86::DIVR_FrST0 },
{ X86::DIV_Fp80 , X86::DIVR_FrST0 },
{ X86::MUL_Fp32 , X86::MUL_FrST0 }, // commutative
{ X86::MUL_Fp64 , X86::MUL_FrST0 }, // commutative
{ X86::MUL_Fp80 , X86::MUL_FrST0 }, // commutative
{ X86::SUB_Fp32 , X86::SUBR_FrST0 },
{ X86::SUB_Fp64 , X86::SUBR_FrST0 },
{ X86::SUB_Fp80 , X86::SUBR_FrST0 },
};
// ReverseSTiTable - Map: A = B op C into: ST(i) = ST(i) op ST(0)
static const TableEntry ReverseSTiTable[] = {
{ X86::ADD_Fp32 , X86::ADD_FrST0 },
{ X86::ADD_Fp64 , X86::ADD_FrST0 },
{ X86::ADD_Fp80 , X86::ADD_FrST0 },
{ X86::DIV_Fp32 , X86::DIV_FrST0 },
{ X86::DIV_Fp64 , X86::DIV_FrST0 },
{ X86::DIV_Fp80 , X86::DIV_FrST0 },
{ X86::MUL_Fp32 , X86::MUL_FrST0 },
{ X86::MUL_Fp64 , X86::MUL_FrST0 },
{ X86::MUL_Fp80 , X86::MUL_FrST0 },
{ X86::SUB_Fp32 , X86::SUB_FrST0 },
{ X86::SUB_Fp64 , X86::SUB_FrST0 },
{ X86::SUB_Fp80 , X86::SUB_FrST0 },
};
/// handleTwoArgFP - Handle instructions like FADD and friends which are virtual
/// instructions which need to be simplified and possibly transformed.
///
/// Result: ST(0) = fsub ST(0), ST(i)
/// ST(i) = fsub ST(0), ST(i)
/// ST(0) = fsubr ST(0), ST(i)
/// ST(i) = fsubr ST(0), ST(i)
///
void FPS::handleTwoArgFP(MachineBasicBlock::iterator &I) {
ASSERT_SORTED(ForwardST0Table); ASSERT_SORTED(ReverseST0Table);
ASSERT_SORTED(ForwardSTiTable); ASSERT_SORTED(ReverseSTiTable);
MachineInstr *MI = I;
unsigned NumOperands = MI->getDesc().getNumOperands();
assert(NumOperands == 3 && "Illegal TwoArgFP instruction!");
unsigned Dest = getFPReg(MI->getOperand(0));
unsigned Op0 = getFPReg(MI->getOperand(NumOperands-2));
unsigned Op1 = getFPReg(MI->getOperand(NumOperands-1));
bool KillsOp0 = MI->killsRegister(X86::FP0+Op0);
bool KillsOp1 = MI->killsRegister(X86::FP0+Op1);
DebugLoc dl = MI->getDebugLoc();
unsigned TOS = getStackEntry(0);
// One of our operands must be on the top of the stack. If neither is yet, we
// need to move one.
if (Op0 != TOS && Op1 != TOS) { // No operand at TOS?
// We can choose to move either operand to the top of the stack. If one of
// the operands is killed by this instruction, we want that one so that we
// can update right on top of the old version.
if (KillsOp0) {
moveToTop(Op0, I); // Move dead operand to TOS.
TOS = Op0;
} else if (KillsOp1) {
moveToTop(Op1, I);
TOS = Op1;
} else {
// All of the operands are live after this instruction executes, so we
// cannot update on top of any operand. Because of this, we must
// duplicate one of the stack elements to the top. It doesn't matter
// which one we pick.
//
duplicateToTop(Op0, Dest, I);
Op0 = TOS = Dest;
KillsOp0 = true;
}
} else if (!KillsOp0 && !KillsOp1) {
// If we DO have one of our operands at the top of the stack, but we don't
// have a dead operand, we must duplicate one of the operands to a new slot
// on the stack.
duplicateToTop(Op0, Dest, I);
Op0 = TOS = Dest;
KillsOp0 = true;
}
// Now we know that one of our operands is on the top of the stack, and at
// least one of our operands is killed by this instruction.
assert((TOS == Op0 || TOS == Op1) && (KillsOp0 || KillsOp1) &&
"Stack conditions not set up right!");
// We decide which form to use based on what is on the top of the stack, and
// which operand is killed by this instruction.
const TableEntry *InstTable;
bool isForward = TOS == Op0;
bool updateST0 = (TOS == Op0 && !KillsOp1) || (TOS == Op1 && !KillsOp0);
if (updateST0) {
if (isForward)
InstTable = ForwardST0Table;
else
InstTable = ReverseST0Table;
} else {
if (isForward)
InstTable = ForwardSTiTable;
else
InstTable = ReverseSTiTable;
}
int Opcode = Lookup(InstTable, array_lengthof(ForwardST0Table),
MI->getOpcode());
assert(Opcode != -1 && "Unknown TwoArgFP pseudo instruction!");
// NotTOS - The register which is not on the top of stack...
unsigned NotTOS = (TOS == Op0) ? Op1 : Op0;
// Replace the old instruction with a new instruction
MBB->remove(I++);
I = BuildMI(*MBB, I, dl, TII->get(Opcode)).addReg(getSTReg(NotTOS));
// If both operands are killed, pop one off of the stack in addition to
// overwriting the other one.
if (KillsOp0 && KillsOp1 && Op0 != Op1) {
assert(!updateST0 && "Should have updated other operand!");
popStackAfter(I); // Pop the top of stack
}
// Update stack information so that we know the destination register is now on
// the stack.
unsigned UpdatedSlot = getSlot(updateST0 ? TOS : NotTOS);
assert(UpdatedSlot < StackTop && Dest < 7);
Stack[UpdatedSlot] = Dest;
RegMap[Dest] = UpdatedSlot;
MBB->getParent()->DeleteMachineInstr(MI); // Remove the old instruction
}
/// handleCompareFP - Handle FUCOM and FUCOMI instructions, which have two FP
/// register arguments and no explicit destinations.
///
void FPS::handleCompareFP(MachineBasicBlock::iterator &I) {
ASSERT_SORTED(ForwardST0Table); ASSERT_SORTED(ReverseST0Table);
ASSERT_SORTED(ForwardSTiTable); ASSERT_SORTED(ReverseSTiTable);
MachineInstr *MI = I;
unsigned NumOperands = MI->getDesc().getNumOperands();
assert(NumOperands == 2 && "Illegal FUCOM* instruction!");
unsigned Op0 = getFPReg(MI->getOperand(NumOperands-2));
unsigned Op1 = getFPReg(MI->getOperand(NumOperands-1));
bool KillsOp0 = MI->killsRegister(X86::FP0+Op0);
bool KillsOp1 = MI->killsRegister(X86::FP0+Op1);
// Make sure the first operand is on the top of stack, the other one can be
// anywhere.
moveToTop(Op0, I);
// Change from the pseudo instruction to the concrete instruction.
MI->getOperand(0).setReg(getSTReg(Op1));
MI->RemoveOperand(1);
MI->setDesc(TII->get(getConcreteOpcode(MI->getOpcode())));
// If any of the operands are killed by this instruction, free them.
if (KillsOp0) freeStackSlotAfter(I, Op0);
if (KillsOp1 && Op0 != Op1) freeStackSlotAfter(I, Op1);
}
/// handleCondMovFP - Handle two address conditional move instructions. These
/// instructions move a st(i) register to st(0) iff a condition is true. These
/// instructions require that the first operand is at the top of the stack, but
/// otherwise don't modify the stack at all.
void FPS::handleCondMovFP(MachineBasicBlock::iterator &I) {
MachineInstr *MI = I;
unsigned Op0 = getFPReg(MI->getOperand(0));
unsigned Op1 = getFPReg(MI->getOperand(2));
bool KillsOp1 = MI->killsRegister(X86::FP0+Op1);
// The first operand *must* be on the top of the stack.
moveToTop(Op0, I);
// Change the second operand to the stack register that the operand is in.
// Change from the pseudo instruction to the concrete instruction.
MI->RemoveOperand(0);
MI->RemoveOperand(1);
MI->getOperand(0).setReg(getSTReg(Op1));
MI->setDesc(TII->get(getConcreteOpcode(MI->getOpcode())));
// If we kill the second operand, make sure to pop it from the stack.
if (Op0 != Op1 && KillsOp1) {
// Get this value off of the register stack.
freeStackSlotAfter(I, Op1);
}
}
/// handleSpecialFP - Handle special instructions which behave unlike other
/// floating point instructions. This is primarily intended for use by pseudo
/// instructions.
///
void FPS::handleSpecialFP(MachineBasicBlock::iterator &I) {
MachineInstr *MI = I;
switch (MI->getOpcode()) {
default: llvm_unreachable("Unknown SpecialFP instruction!");
case TargetOpcode::COPY: {
// We handle three kinds of copies: FP <- FP, FP <- ST, and ST <- FP.
const MachineOperand &MO1 = MI->getOperand(1);
const MachineOperand &MO0 = MI->getOperand(0);
unsigned DstST = MO0.getReg() - X86::ST0;
unsigned SrcST = MO1.getReg() - X86::ST0;
bool KillsSrc = MI->killsRegister(MO1.getReg());
// ST = COPY FP. Set up a pending ST register.
if (DstST < 8) {
unsigned SrcFP = getFPReg(MO1);
assert(isLive(SrcFP) && "Cannot copy dead register");
assert(!MO0.isDead() && "Cannot copy to dead ST register");
// Unallocated STs are marked as the nonexistent FP255.
while (NumPendingSTs <= DstST)
PendingST[NumPendingSTs++] = NumFPRegs;
// STi could still be live from a previous inline asm.
if (isScratchReg(PendingST[DstST])) {
DEBUG(dbgs() << "Clobbering old ST in FP" << unsigned(PendingST[DstST])
<< '\n');
freeStackSlotBefore(MI, PendingST[DstST]);
}
// When the source is killed, allocate a scratch FP register.
if (KillsSrc) {
duplicatePendingSTBeforeKill(SrcFP, I);
unsigned Slot = getSlot(SrcFP);
unsigned SR = getScratchReg();
PendingST[DstST] = SR;
Stack[Slot] = SR;
RegMap[SR] = Slot;
} else
PendingST[DstST] = SrcFP;
break;
}
// FP = COPY ST. Extract fixed stack value.
// Any instruction defining ST registers must have assigned them to a
// scratch register.
if (SrcST < 8) {
unsigned DstFP = getFPReg(MO0);
assert(!isLive(DstFP) && "Cannot copy ST to live FP register");
assert(NumPendingSTs > SrcST && "Cannot copy from dead ST register");
unsigned SrcFP = PendingST[SrcST];
assert(isScratchReg(SrcFP) && "Expected ST in a scratch register");
assert(isLive(SrcFP) && "Scratch holding ST is dead");
// DstFP steals the stack slot from SrcFP.
unsigned Slot = getSlot(SrcFP);
Stack[Slot] = DstFP;
RegMap[DstFP] = Slot;
// Always treat the ST as killed.
PendingST[SrcST] = NumFPRegs;
while (NumPendingSTs && PendingST[NumPendingSTs - 1] == NumFPRegs)
--NumPendingSTs;
break;
}
// FP <- FP copy.
unsigned DstFP = getFPReg(MO0);
unsigned SrcFP = getFPReg(MO1);
assert(isLive(SrcFP) && "Cannot copy dead register");
if (KillsSrc) {
// If the input operand is killed, we can just change the owner of the
// incoming stack slot into the result.
unsigned Slot = getSlot(SrcFP);
Stack[Slot] = DstFP;
RegMap[DstFP] = Slot;
} else {
// For COPY we just duplicate the specified value to a new stack slot.
// This could be made better, but would require substantial changes.
duplicateToTop(SrcFP, DstFP, I);
}
break;
}
case TargetOpcode::IMPLICIT_DEF: {
// All FP registers must be explicitly defined, so load a 0 instead.
unsigned Reg = MI->getOperand(0).getReg() - X86::FP0;
DEBUG(dbgs() << "Emitting LD_F0 for implicit FP" << Reg << '\n');
BuildMI(*MBB, I, MI->getDebugLoc(), TII->get(X86::LD_F0));
pushReg(Reg);
break;
}
case X86::FpPOP_RETVAL: {
// The FpPOP_RETVAL instruction is used after calls that return a value on
// the floating point stack. We cannot model this with ST defs since CALL
// instructions have fixed clobber lists. This instruction is interpreted
// to mean that there is one more live register on the stack than we
// thought.
//
// This means that StackTop does not match the hardware stack between a
// call and the FpPOP_RETVAL instructions. We do tolerate FP instructions
// between CALL and FpPOP_RETVAL as long as they don't overflow the
// hardware stack.
unsigned DstFP = getFPReg(MI->getOperand(0));
// Move existing stack elements up to reflect reality.
assert(StackTop < 8 && "Stack overflowed before FpPOP_RETVAL");
if (StackTop) {
std::copy_backward(Stack, Stack + StackTop, Stack + StackTop + 1);
for (unsigned i = 0; i != NumFPRegs; ++i)
++RegMap[i];
}
++StackTop;
// DstFP is the new bottom of the stack.
Stack[0] = DstFP;
RegMap[DstFP] = 0;
// DstFP will be killed by processBasicBlock if this was a dead def.
break;
}
case TargetOpcode::INLINEASM: {
// The inline asm MachineInstr currently only *uses* FP registers for the
// 'f' constraint. These should be turned into the current ST(x) register
// in the machine instr.
//
// There are special rules for x87 inline assembly. The compiler must know
// exactly how many registers are popped and pushed implicitly by the asm.
// Otherwise it is not possible to restore the stack state after the inline
// asm.
//
// There are 3 kinds of input operands:
//
// 1. Popped inputs. These must appear at the stack top in ST0-STn. A
// popped input operand must be in a fixed stack slot, and it is either
// tied to an output operand, or in the clobber list. The MI has ST use
// and def operands for these inputs.
//
// 2. Fixed inputs. These inputs appear in fixed stack slots, but are
// preserved by the inline asm. The fixed stack slots must be STn-STm
// following the popped inputs. A fixed input operand cannot be tied to
// an output or appear in the clobber list. The MI has ST use operands
// and no defs for these inputs.
//
// 3. Preserved inputs. These inputs use the "f" constraint which is
// represented as an FP register. The inline asm won't change these
// stack slots.
//
// Outputs must be in ST registers, FP outputs are not allowed. Clobbered
// registers do not count as output operands. The inline asm changes the
// stack as if it popped all the popped inputs and then pushed all the
// output operands.
// Scan the assembly for ST registers used, defined and clobbered. We can
// only tell clobbers from defs by looking at the asm descriptor.
unsigned STUses = 0, STDefs = 0, STClobbers = 0, STDeadDefs = 0;
unsigned NumOps = 0;
for (unsigned i = InlineAsm::MIOp_FirstOperand, e = MI->getNumOperands();
i != e && MI->getOperand(i).isImm(); i += 1 + NumOps) {
unsigned Flags = MI->getOperand(i).getImm();
NumOps = InlineAsm::getNumOperandRegisters(Flags);
if (NumOps != 1)
continue;
const MachineOperand &MO = MI->getOperand(i + 1);
if (!MO.isReg())
continue;
unsigned STReg = MO.getReg() - X86::ST0;
if (STReg >= 8)
continue;
switch (InlineAsm::getKind(Flags)) {
case InlineAsm::Kind_RegUse:
STUses |= (1u << STReg);
break;
case InlineAsm::Kind_RegDef:
case InlineAsm::Kind_RegDefEarlyClobber:
STDefs |= (1u << STReg);
if (MO.isDead())
STDeadDefs |= (1u << STReg);
break;
case InlineAsm::Kind_Clobber:
STClobbers |= (1u << STReg);
break;
default:
break;
}
}
if (STUses && !isMask_32(STUses))
MI->emitError("fixed input regs must be last on the x87 stack");
unsigned NumSTUses = CountTrailingOnes_32(STUses);
// Defs must be contiguous from the stack top. ST0-STn.
if (STDefs && !isMask_32(STDefs)) {
MI->emitError("output regs must be last on the x87 stack");
STDefs = NextPowerOf2(STDefs) - 1;
}
unsigned NumSTDefs = CountTrailingOnes_32(STDefs);
// So must the clobbered stack slots. ST0-STm, m >= n.
if (STClobbers && !isMask_32(STDefs | STClobbers))
MI->emitError("clobbers must be last on the x87 stack");
// Popped inputs are the ones that are also clobbered or defined.
unsigned STPopped = STUses & (STDefs | STClobbers);
if (STPopped && !isMask_32(STPopped))
MI->emitError("implicitly popped regs must be last on the x87 stack");
unsigned NumSTPopped = CountTrailingOnes_32(STPopped);
DEBUG(dbgs() << "Asm uses " << NumSTUses << " fixed regs, pops "
<< NumSTPopped << ", and defines " << NumSTDefs << " regs.\n");
// Scan the instruction for FP uses corresponding to "f" constraints.
// Collect FP registers to kill afer the instruction.
// Always kill all the scratch regs.
unsigned FPKills = ((1u << NumFPRegs) - 1) & ~0xff;
unsigned FPUsed = 0;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &Op = MI->getOperand(i);
if (!Op.isReg() || Op.getReg() < X86::FP0 || Op.getReg() > X86::FP6)
continue;
if (!Op.isUse())
MI->emitError("illegal \"f\" output constraint");
unsigned FPReg = getFPReg(Op);
FPUsed |= 1U << FPReg;
// If we kill this operand, make sure to pop it from the stack after the
// asm. We just remember it for now, and pop them all off at the end in
// a batch.
if (Op.isKill())
FPKills |= 1U << FPReg;
}
// The popped inputs will be killed by the instruction, so duplicate them
// if the FP register needs to be live after the instruction, or if it is
// used in the instruction itself. We effectively treat the popped inputs
// as early clobbers.
for (unsigned i = 0; i < NumSTPopped; ++i) {
if ((FPKills & ~FPUsed) & (1u << PendingST[i]))
continue;
unsigned SR = getScratchReg();
duplicateToTop(PendingST[i], SR, I);
DEBUG(dbgs() << "Duplicating ST" << i << " in FP"
<< unsigned(PendingST[i]) << " to avoid clobbering it.\n");
PendingST[i] = SR;
}
// Make sure we have a unique live register for every fixed use. Some of
// them could be undef uses, and we need to emit LD_F0 instructions.
for (unsigned i = 0; i < NumSTUses; ++i) {
if (i < NumPendingSTs && PendingST[i] < NumFPRegs) {
// Check for shared assignments.
for (unsigned j = 0; j < i; ++j) {
if (PendingST[j] != PendingST[i])
continue;
// STi and STj are inn the same register, create a copy.
unsigned SR = getScratchReg();
duplicateToTop(PendingST[i], SR, I);
DEBUG(dbgs() << "Duplicating ST" << i << " in FP"
<< unsigned(PendingST[i])
<< " to avoid collision with ST" << j << '\n');
PendingST[i] = SR;
}
continue;
}
unsigned SR = getScratchReg();
DEBUG(dbgs() << "Emitting LD_F0 for ST" << i << " in FP" << SR << '\n');
BuildMI(*MBB, I, MI->getDebugLoc(), TII->get(X86::LD_F0));
pushReg(SR);
PendingST[i] = SR;
if (NumPendingSTs == i)
++NumPendingSTs;
}
assert(NumPendingSTs >= NumSTUses && "Fixed registers should be assigned");
// Now we can rearrange the live registers to match what was requested.
shuffleStackTop(PendingST, NumPendingSTs, I);
DEBUG({dbgs() << "Before asm: "; dumpStack();});
// With the stack layout fixed, rewrite the FP registers.
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &Op = MI->getOperand(i);
if (!Op.isReg() || Op.getReg() < X86::FP0 || Op.getReg() > X86::FP6)
continue;
unsigned FPReg = getFPReg(Op);
Op.setReg(getSTReg(FPReg));
}
// Simulate the inline asm popping its inputs and pushing its outputs.
StackTop -= NumSTPopped;
// Hold the fixed output registers in scratch FP registers. They will be
// transferred to real FP registers by copies.
NumPendingSTs = 0;
for (unsigned i = 0; i < NumSTDefs; ++i) {
unsigned SR = getScratchReg();
pushReg(SR);
FPKills &= ~(1u << SR);
}
for (unsigned i = 0; i < NumSTDefs; ++i)
PendingST[NumPendingSTs++] = getStackEntry(i);
DEBUG({dbgs() << "After asm: "; dumpStack();});
// If any of the ST defs were dead, pop them immediately. Our caller only
// handles dead FP defs.
MachineBasicBlock::iterator InsertPt = MI;
for (unsigned i = 0; STDefs & (1u << i); ++i) {
if (!(STDeadDefs & (1u << i)))
continue;
freeStackSlotAfter(InsertPt, PendingST[i]);
PendingST[i] = NumFPRegs;
}
while (NumPendingSTs && PendingST[NumPendingSTs - 1] == NumFPRegs)
--NumPendingSTs;
// If this asm kills any FP registers (is the last use of them) we must
// explicitly emit pop instructions for them. Do this now after the asm has
// executed so that the ST(x) numbers are not off (which would happen if we
// did this inline with operand rewriting).
//
// Note: this might be a non-optimal pop sequence. We might be able to do
// better by trying to pop in stack order or something.
while (FPKills) {
unsigned FPReg = CountTrailingZeros_32(FPKills);
if (isLive(FPReg))
freeStackSlotAfter(InsertPt, FPReg);
FPKills &= ~(1U << FPReg);
}
// Don't delete the inline asm!
return;
}
case X86::RET:
case X86::RETI:
// If RET has an FP register use operand, pass the first one in ST(0) and
// the second one in ST(1).
// Find the register operands.
unsigned FirstFPRegOp = ~0U, SecondFPRegOp = ~0U;
unsigned LiveMask = 0;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &Op = MI->getOperand(i);
if (!Op.isReg() || Op.getReg() < X86::FP0 || Op.getReg() > X86::FP6)
continue;
// FP Register uses must be kills unless there are two uses of the same
// register, in which case only one will be a kill.
assert(Op.isUse() &&
(Op.isKill() || // Marked kill.
getFPReg(Op) == FirstFPRegOp || // Second instance.
MI->killsRegister(Op.getReg())) && // Later use is marked kill.
"Ret only defs operands, and values aren't live beyond it");
if (FirstFPRegOp == ~0U)
FirstFPRegOp = getFPReg(Op);
else {
assert(SecondFPRegOp == ~0U && "More than two fp operands!");
SecondFPRegOp = getFPReg(Op);
}
LiveMask |= (1 << getFPReg(Op));
// Remove the operand so that later passes don't see it.
MI->RemoveOperand(i);
--i, --e;
}
// We may have been carrying spurious live-ins, so make sure only the returned
// registers are left live.
adjustLiveRegs(LiveMask, MI);
if (!LiveMask) return; // Quick check to see if any are possible.
// There are only four possibilities here:
// 1) we are returning a single FP value. In this case, it has to be in
// ST(0) already, so just declare success by removing the value from the
// FP Stack.
if (SecondFPRegOp == ~0U) {
// Assert that the top of stack contains the right FP register.
assert(StackTop == 1 && FirstFPRegOp == getStackEntry(0) &&
"Top of stack not the right register for RET!");
// Ok, everything is good, mark the value as not being on the stack
// anymore so that our assertion about the stack being empty at end of
// block doesn't fire.
StackTop = 0;
return;
}
// Otherwise, we are returning two values:
// 2) If returning the same value for both, we only have one thing in the FP
// stack. Consider: RET FP1, FP1
if (StackTop == 1) {
assert(FirstFPRegOp == SecondFPRegOp && FirstFPRegOp == getStackEntry(0)&&
"Stack misconfiguration for RET!");
// Duplicate the TOS so that we return it twice. Just pick some other FPx
// register to hold it.
unsigned NewReg = getScratchReg();
duplicateToTop(FirstFPRegOp, NewReg, MI);
FirstFPRegOp = NewReg;
}
/// Okay we know we have two different FPx operands now:
assert(StackTop == 2 && "Must have two values live!");
/// 3) If SecondFPRegOp is currently in ST(0) and FirstFPRegOp is currently
/// in ST(1). In this case, emit an fxch.
if (getStackEntry(0) == SecondFPRegOp) {
assert(getStackEntry(1) == FirstFPRegOp && "Unknown regs live");
moveToTop(FirstFPRegOp, MI);
}
/// 4) Finally, FirstFPRegOp must be in ST(0) and SecondFPRegOp must be in
/// ST(1). Just remove both from our understanding of the stack and return.
assert(getStackEntry(0) == FirstFPRegOp && "Unknown regs live");
assert(getStackEntry(1) == SecondFPRegOp && "Unknown regs live");
StackTop = 0;
return;
}
I = MBB->erase(I); // Remove the pseudo instruction
// We want to leave I pointing to the previous instruction, but what if we
// just erased the first instruction?
if (I == MBB->begin()) {
DEBUG(dbgs() << "Inserting dummy KILL\n");
I = BuildMI(*MBB, I, DebugLoc(), TII->get(TargetOpcode::KILL));
} else
--I;
}
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