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* Fix several register aliasing bugs 

* Add a new option to eliminate spilling of registers that are only used
  within a basic block.

llvm-svn: 5106
This commit is contained in:
Chris Lattner 2002-12-18 08:14:26 +00:00
parent 07b2da5d67
commit d4627093de
1 changed files with 148 additions and 39 deletions
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187
llvm/lib/CodeGen/RegAllocLocal.cpp
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@ -10,11 +10,14 @@
#include "llvm/Target/MachineInstrInfo.h"
#include "llvm/Target/TargetMachine.h"
#include "Support/Statistic.h"
#include "Support/CommandLine.h"
#include <iostream>
namespace {
Statistic<> NumSpilled ("ra-local", "Number of registers spilled");
Statistic<> NumReloaded("ra-local", "Number of registers reloaded");
cl::opt<bool> DisableKill("no-kill", cl::Hidden,
cl::desc("Disable register kill in local-ra"));
class RA : public FunctionPass {
TargetMachine &TM;
@ -49,15 +52,23 @@ namespace {
//
std::vector<unsigned> PhysRegsUseOrder;
// LastUserOf map - This multimap contains the set of registers that each
// key instruction is the last user of. If an instruction has an entry in
// this map, that means that the specified operands are killed after the
// instruction is executed, thus they don't need to be spilled into memory
//
std::multimap<MachineInstr*, unsigned> LastUserOf;
void MarkPhysRegRecentlyUsed(unsigned Reg) {
assert(std::find(PhysRegsUseOrder.begin(), PhysRegsUseOrder.end(), Reg) !=
PhysRegsUseOrder.end() && "Register isn't used yet!");
assert(!PhysRegsUseOrder.empty() && "No registers used!");
if (PhysRegsUseOrder.back() != Reg) {
for (unsigned i = PhysRegsUseOrder.size(); ; --i)
if (PhysRegsUseOrder[i-1] == Reg) { // remove from middle
for (unsigned i = PhysRegsUseOrder.size(); i != 0; --i)
if (areRegsEqual(Reg, PhysRegsUseOrder[i-1])) { // remove from middle
unsigned RegMatch = PhysRegsUseOrder[i-1];
PhysRegsUseOrder.erase(PhysRegsUseOrder.begin()+i-1);
PhysRegsUseOrder.push_back(Reg); // Add it to the end of the list
return;
PhysRegsUseOrder.push_back(RegMatch); // Add it to the end of the list
if (RegMatch == Reg)
return; // Found an exact match, exit early
}
}
}
@ -88,6 +99,16 @@ namespace {
/// in predecessor basic blocks.
void EliminatePHINodes(MachineBasicBlock &MBB);
/// CalculateLastUseOfVReg - Calculate an approximation of the killing
/// uses for the virtual registers in the function. Here we try to capture
/// registers that are defined and only used within the same basic block.
/// Because we don't have use-def chains yet, we have to do this the hard
/// way.
///
void CalculateLastUseOfVReg(MachineBasicBlock &MBB,
std::map<unsigned, MachineInstr*> &LastUseOfVReg) const;
/// EmitPrologue/EmitEpilogue - Use the register info object to add a
/// prologue/epilogue to the function and save/restore any callee saved
/// registers we are responsible for.
@ -95,21 +116,23 @@ namespace {
void EmitPrologue();
void EmitEpilogue(MachineBasicBlock &MBB);
/// areRegsEqual - This method returns true if the specified registers are
/// related to each other. To do this, it checks to see if they are equal
/// or if the first register is in the alias set of the second register.
///
bool areRegsEqual(unsigned R1, unsigned R2) const {
if (R1 == R2) return true;
if (const unsigned *AliasSet = RegInfo.getAliasSet(R2))
for (unsigned i = 0; AliasSet[i]; ++i)
if (AliasSet[i] == R1) return true;
return false;
}
/// isAllocatableRegister - A register may be used by the program if it's
/// not the stack or frame pointer.
bool isAllocatableRegister(unsigned R) const {
unsigned FP = RegInfo.getFramePointer(), SP = RegInfo.getStackPointer();
// Don't allocate the Frame or Stack pointers
if (R == FP || R == SP)
return false;
// Check to see if this register aliases the stack or frame pointer...
if (const unsigned *AliasSet = RegInfo.getAliasSet(R)) {
for (unsigned i = 0; AliasSet[i]; ++i)
if (AliasSet[i] == FP || AliasSet[i] == SP)
return false;
}
return true;
return !areRegsEqual(FP, R) && !areRegsEqual(SP, R);
}
/// getStackSpaceFor - This returns the offset of the specified virtual
@ -122,6 +145,7 @@ namespace {
NumBytesAllocated = 4; // FIXME: This is X86 specific
}
void removePhysReg(unsigned PhysReg);
/// spillVirtReg - This method spills the value specified by PhysReg into
/// the virtual register slot specified by VirtReg. It then updates the RA
@ -136,8 +160,17 @@ namespace {
void spillPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
unsigned PhysReg) {
std::map<unsigned, unsigned>::iterator PI = PhysRegsUsed.find(PhysReg);
if (PI != PhysRegsUsed.end()) // Only spill it if it's used!
if (PI != PhysRegsUsed.end()) { // Only spill it if it's used!
spillVirtReg(MBB, I, PI->second, PhysReg);
} else if (const unsigned *AliasSet = RegInfo.getAliasSet(PhysReg)) {
// If the selected register aliases any other registers, we must make sure
// that one of the aliases isn't alive...
for (unsigned i = 0; AliasSet[i]; ++i) {
PI = PhysRegsUsed.find(AliasSet[i]);
if (PI != PhysRegsUsed.end()) // Spill aliased register...
spillVirtReg(MBB, I, PI->second, AliasSet[i]);
}
}
}
void AssignVirtToPhysReg(unsigned VirtReg, unsigned PhysReg);
@ -146,7 +179,7 @@ namespace {
/// free and available for use. This also includes checking to see if
/// aliased registers are all free...
///
bool RA::isPhysRegAvailable(unsigned PhysReg) const;
bool isPhysRegAvailable(unsigned PhysReg) const;
/// getFreeReg - Find a physical register to hold the specified virtual
/// register. If all compatible physical registers are used, this method
@ -196,6 +229,19 @@ unsigned RA::getStackSpaceFor(unsigned VirtReg,
}
/// removePhysReg - This method marks the specified physical register as no
/// longer being in use.
///
void RA::removePhysReg(unsigned PhysReg) {
PhysRegsUsed.erase(PhysReg); // PhyReg no longer used
std::vector<unsigned>::iterator It =
std::find(PhysRegsUseOrder.begin(), PhysRegsUseOrder.end(), PhysReg);
assert(It != PhysRegsUseOrder.end() &&
"Spilled a physical register, but it was not in use list!");
PhysRegsUseOrder.erase(It);
}
/// spillVirtReg - This method spills the value specified by PhysReg into the
/// virtual register slot specified by VirtReg. It then updates the RA data
/// structures to indicate the fact that PhysReg is now available.
@ -213,13 +259,8 @@ void RA::spillVirtReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
++NumSpilled; // Update statistics
Virt2PhysRegMap.erase(VirtReg); // VirtReg no longer available
}
PhysRegsUsed.erase(PhysReg); // PhyReg no longer used
std::vector<unsigned>::iterator It =
std::find(PhysRegsUseOrder.begin(), PhysRegsUseOrder.end(), PhysReg);
assert(It != PhysRegsUseOrder.end() &&
"Spilled a physical register, but it was not in use list!");
PhysRegsUseOrder.erase(It);
removePhysReg(PhysReg);
}
@ -300,13 +341,6 @@ unsigned RA::getFreeReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator &I,
// At this point PhysRegsUseOrder[i] is the least recently used register of
// compatible register class. Spill it to memory and reap its remains.
spillPhysReg(MBB, I, PhysReg);
// If the selected register aliases any other registers, we must make sure
// to spill them as well...
if (const unsigned *AliasSet = RegInfo.getAliasSet(PhysReg))
for (unsigned i = 0; AliasSet[i]; ++i)
if (PhysRegsUsed.count(AliasSet[i])) // Spill aliased register...
spillPhysReg(MBB, I, AliasSet[i]);
}
// Now that we know which register we need to assign this to, do it now!
@ -352,6 +386,41 @@ unsigned RA::reloadVirtReg(MachineBasicBlock &MBB,
return PhysReg;
}
/// CalculateLastUseOfVReg - Calculate an approximation of the killing uses for
/// the virtual registers in the function. Here we try to capture registers
/// that are defined and only used within the same basic block. Because we
/// don't have use-def chains yet, we have to do this the hard way.
///
void RA::CalculateLastUseOfVReg(MachineBasicBlock &MBB,
std::map<unsigned, MachineInstr*> &LastUseOfVReg) const {
// Calculate the last machine instruction in this basic block that uses the
// specified virtual register defined in this basic block.
std::map<unsigned, MachineInstr*> LastLocalUses;
for (MachineBasicBlock::iterator I = MBB.begin(), E = MBB.end(); I != E;++I){
MachineInstr *MI = *I;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &Op = MI->getOperand(i);
if (Op.isVirtualRegister()) {
if (Op.opIsDef()) { // Definition of a new virtual reg?
LastLocalUses[Op.getAllocatedRegNum()] = 0; // Record it
} else { // Use of a virtual reg.
std::map<unsigned, MachineInstr*>::iterator It =
LastLocalUses.find(Op.getAllocatedRegNum());
if (It != LastLocalUses.end()) // Local use?
It->second = MI; // Update last use
else
LastUseOfVReg[Op.getAllocatedRegNum()] = 0;
}
}
}
}
// Move local uses over... if there are any uses of a local already in the
// lastuse map, the newly inserted entry is ignored.
LastUseOfVReg.insert(LastLocalUses.begin(), LastLocalUses.end());
}
/// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions in
/// predecessor basic blocks.
@ -364,7 +433,6 @@ void RA::EliminatePHINodes(MachineBasicBlock &MBB) {
// Unlink the PHI node from the basic block... but don't delete the PHI yet
MBB.erase(MBB.begin());
DEBUG(std::cerr << "num ops: " << MI->getNumOperands() << "\n");
assert(MI->getOperand(0).isVirtualRegister() &&
"PHI node doesn't write virt reg?");
@ -448,9 +516,15 @@ void RA::AllocateBasicBlock(MachineBasicBlock &MBB) {
if (const unsigned *ImplicitDefs = MID.ImplicitDefs)
for (unsigned i = 0; ImplicitDefs[i]; ++i) {
unsigned Reg = ImplicitDefs[i];
spillPhysReg(MBB, I, Reg);
PhysRegsUsed[Reg] = 0; // It's free now, and it's reserved
PhysRegsUseOrder.push_back(Reg);
// We don't want to spill implicit definitions if they were explicitly
// chosen. For this reason, check to see now if the register we are
// to spill has a vreg of 0.
if (PhysRegsUsed.count(Reg) && PhysRegsUsed[Reg] != 0) {
spillPhysReg(MBB, I, Reg);
PhysRegsUsed[Reg] = 0; // It's free now, and it's reserved
PhysRegsUseOrder.push_back(Reg);
}
}
// Loop over the implicit uses, making sure that they are at the head of the
@ -475,7 +549,7 @@ void RA::AllocateBasicBlock(MachineBasicBlock &MBB) {
// that would be destroyed by defs of this instruction. Loop over the
// implicit defs and assign them to a register, spilling the incoming value
// if we need to scavange a register.
//
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i)
if (MI->getOperand(i).opIsDef() &&
!MI->getOperand(i).isPhysicalRegister()) {
@ -500,6 +574,23 @@ void RA::AllocateBasicBlock(MachineBasicBlock &MBB) {
}
MI->SetMachineOperandReg(i, DestPhysReg); // Assign the output register
}
if (!DisableKill) {
// If this instruction is the last user of anything in registers, kill the
// value, freeing the register being used, so it doesn't need to be spilled
// to memory at the end of the block.
std::multimap<MachineInstr*, unsigned>::iterator LUOI =
LastUserOf.lower_bound(MI);
for (; LUOI != LastUserOf.end() && LUOI->first == MI; ++MI) {// entry found?
unsigned VirtReg = LUOI->second;
unsigned PhysReg = Virt2PhysRegMap[VirtReg];
if (PhysReg) {
DEBUG(std::cout << "V: " << VirtReg << " P: " << PhysReg << " Last use of: " << *MI);
removePhysReg(PhysReg);
}
Virt2PhysRegMap.erase(VirtReg);
}
}
}
// Rewind the iterator to point to the first flow control instruction...
@ -578,13 +669,30 @@ bool RA::runOnMachineFunction(MachineFunction &Fn) {
MF = &Fn;
// First pass: eliminate PHI instructions by inserting copies into predecessor
// blocks.
// FIXME: In this pass, count how many uses of each VReg exist!
// blocks, and calculate a simple approximation of killing uses for virtual
// registers.
//
std::map<unsigned, MachineInstr*> LastUseOfVReg;
for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
MBB != MBBe; ++MBB) {
if (!DisableKill)
CalculateLastUseOfVReg(*MBB, LastUseOfVReg);
EliminatePHINodes(*MBB);
}
// At this point LastUseOfVReg has been filled in to contain the last
// MachineInstr user of the specified virtual register, if that user is
// within the same basic block as the definition (otherwise it contains
// null). Invert this mapping now:
if (!DisableKill)
for (std::map<unsigned, MachineInstr*>::iterator I = LastUseOfVReg.begin(),
E = LastUseOfVReg.end(); I != E; ++I)
if (I->second)
LastUserOf.insert(std::make_pair(I->second, I->first));
// We're done with the temporary list now.
LastUseOfVReg.clear();
// Loop over all of the basic blocks, eliminating virtual register references
for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
MBB != MBBe; ++MBB)
@ -604,6 +712,7 @@ bool RA::runOnMachineFunction(MachineFunction &Fn) {
EmitEpilogue(*MBB);
}
LastUserOf.clear();
cleanupAfterFunction();
return true;
}