llvm-6502/lib/Target/SparcV9/SparcV9PeepholeOpts.cpp
2003-09-01 20:38:03 +00:00

158 lines
5.8 KiB
C++

//===-- PeepholeOpts.cpp --------------------------------------------------===//
//
// Support for performing several peephole opts in one or a few passes over the
// machine code of a method.
//
//===----------------------------------------------------------------------===//
#include "SparcInternals.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/BasicBlock.h"
#include "llvm/Pass.h"
//************************* Internal Functions *****************************/
static inline void
DeleteInstruction(MachineBasicBlock& mvec,
MachineBasicBlock::iterator& BBI,
const TargetMachine& target) {
// Check if this instruction is in a delay slot of its predecessor.
if (BBI != mvec.begin()) {
const TargetInstrInfo& mii = target.getInstrInfo();
MachineInstr* predMI = *(BBI-1);
if (unsigned ndelay = mii.getNumDelaySlots(predMI->getOpCode())) {
// This instruction is in a delay slot of its predecessor, so
// replace it with a nop. By replacing in place, we save having
// to update the I-I maps.
//
assert(ndelay == 1 && "Not yet handling multiple-delay-slot targets");
(*BBI)->replace(mii.getNOPOpCode(), 0);
return;
}
}
// The instruction is not in a delay slot, so we can simply erase it.
mvec.erase(BBI);
BBI = mvec.end();
}
//******************* Individual Peephole Optimizations ********************/
//----------------------------------------------------------------------------
// Function: IsUselessCopy
// Decide whether a machine instruction is a redundant copy:
// -- ADD with g0 and result and operand are identical, or
// -- OR with g0 and result and operand are identical, or
// -- FMOVS or FMOVD and result and operand are identical.
// Other cases are possible but very rare that they would be useless copies,
// so it's not worth analyzing them.
//----------------------------------------------------------------------------
static bool IsUselessCopy(const TargetMachine &target, const MachineInstr* MI) {
if (MI->getOpCode() == V9::FMOVS || MI->getOpCode() == V9::FMOVD) {
return (/* both operands are allocated to the same register */
MI->getOperand(0).getAllocatedRegNum() ==
MI->getOperand(1).getAllocatedRegNum());
} else if (MI->getOpCode() == V9::ADDr || MI->getOpCode() == V9::ORr) {
unsigned srcWithDestReg;
for (srcWithDestReg = 0; srcWithDestReg < 2; ++srcWithDestReg)
if (MI->getOperand(srcWithDestReg).hasAllocatedReg() &&
MI->getOperand(srcWithDestReg).getAllocatedRegNum()
== MI->getOperand(2).getAllocatedRegNum())
break;
if (srcWithDestReg == 2)
return false;
else {
/* else source and dest are allocated to the same register */
unsigned otherOp = 1 - srcWithDestReg;
return (/* either operand otherOp is register %g0 */
(MI->getOperand(otherOp).hasAllocatedReg() &&
MI->getOperand(otherOp).getAllocatedRegNum() ==
target.getRegInfo().getZeroRegNum()) ||
/* or operand otherOp == 0 */
(MI->getOperand(otherOp).getType()
== MachineOperand::MO_SignExtendedImmed &&
MI->getOperand(otherOp).getImmedValue() == 0));
}
}
else
return false;
}
inline bool
RemoveUselessCopies(MachineBasicBlock& mvec,
MachineBasicBlock::iterator& BBI,
const TargetMachine& target) {
if (IsUselessCopy(target, *BBI)) {
DeleteInstruction(mvec, BBI, target);
return true;
}
return false;
}
//************************ Class Implementations **************************/
class PeepholeOpts: public BasicBlockPass {
const TargetMachine &target;
bool visit(MachineBasicBlock& mvec,
MachineBasicBlock::iterator BBI) const;
public:
PeepholeOpts(const TargetMachine &T): target(T) { }
bool runOnBasicBlock(BasicBlock &BB); // apply this pass to each BB
virtual const char *getPassName() const { return "Peephole Optimization"; }
};
// Apply a list of peephole optimizations to this machine instruction
// within its local context. They are allowed to delete MI or any
// instruction before MI, but not
//
bool PeepholeOpts::visit(MachineBasicBlock& mvec,
MachineBasicBlock::iterator BBI) const {
/* Remove redundant copy instructions */
return RemoveUselessCopies(mvec, BBI, target);
}
bool PeepholeOpts::runOnBasicBlock(BasicBlock &BB) {
// Get the machine instructions for this BB
// FIXME: MachineBasicBlock::get() is deprecated, hence inlining the function
const Function *F = BB.getParent();
MachineFunction &MF = MachineFunction::get(F);
MachineBasicBlock *MBB = NULL;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I)
if (I->getBasicBlock() == &BB)
MBB = I;
assert(MBB && "MachineBasicBlock object not found for specified block!");
MachineBasicBlock &mvec = *MBB;
// Iterate over all machine instructions in the BB
// Use a reverse iterator to allow deletion of MI or any instruction after it.
// Insertions or deletions *before* MI are not safe.
//
for (MachineBasicBlock::reverse_iterator RI=mvec.rbegin(),
RE=mvec.rend(); RI != RE; ) {
MachineBasicBlock::iterator BBI = RI.base()-1; // save before incr
++RI; // pre-increment to delete MI or after it
visit(mvec, BBI);
}
return true;
}
//===----------------------------------------------------------------------===//
// createPeepholeOptsPass - Public entrypoint for peephole optimization
// and this file as a whole...
//
FunctionPass* createPeepholeOptsPass(TargetMachine &T) {
return new PeepholeOpts(T);
}