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Simplify PHI node elimination significantly by doing it as a prepass to

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register allocation


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@5066 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2002-12-15 22:39:53 +00:00
parent f4b95d94e2
commit 8ed9eb5ca3
1 changed files with 13 additions and 30 deletions
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43
lib/CodeGen/RegAllocSimple.cpp
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@ -212,6 +212,7 @@ RegAllocSimple::saveVirtRegToStack (MachineBasicBlock &MBB,
/// EliminatePHINodes - Eliminate phi nodes by inserting copy instructions in
/// predecessor basic blocks.
///
void RegAllocSimple::EliminatePHINodes(MachineBasicBlock &MBB) {
const MachineInstrInfo &MII = TM.getInstrInfo();
@ -220,26 +221,12 @@ void RegAllocSimple::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 invalid regs: " << RegsUsed.size() << "\n");
DEBUG(std::cerr << "num ops: " << MI->getNumOperands() << "\n");
assert(MI->getOperand(0).isVirtualRegister() &&
"PHI node doesn't write virt reg?");
// a preliminary pass that will invalidate any registers that
// are used by the instruction (including implicit uses)
invalidatePhysRegs(MI);
// Allocate a physical reg to hold this temporary.
//
unsigned virtualReg = MI->getOperand(0).getAllocatedRegNum();
unsigned physReg = getFreeReg(virtualReg);
// Find the register class of the target register: should be the
// same as the values we're trying to store there
const TargetRegisterClass* regClass = MF->getRegClass(virtualReg);
assert(regClass && "Target register class not found!");
unsigned dataSize = regClass->getDataSize();
for (int i = MI->getNumOperands() - 1; i >= 2; i-=2) {
MachineOperand &opVal = MI->getOperand(i-1);
@ -274,27 +261,20 @@ void RegAllocSimple::EliminatePHINodes(MachineBasicBlock &MBB) {
// are inserted right in front of it and not in front of a non-branch
if (!MII.isBranch(opMI->getOpcode()))
++opI;
unsigned dataSize = MF->getRegClass(virtualReg)->getDataSize();
// Retrieve the constant value from this op, move it to target
// register of the phi
if (opVal.isImmediate()) {
opI = RegInfo->moveImm2Reg(opBlock, opI, physReg,
opI = RegInfo->moveImm2Reg(opBlock, opI, virtualReg,
(unsigned) opVal.getImmedValue(),
dataSize);
} else {
// Allocate a physical register and add a move in the BB
unsigned opVirtualReg = opVal.getAllocatedRegNum();
unsigned opPhysReg;
opI = moveUseToReg(opBlock, opI, opVirtualReg, physReg);
opI = RegInfo->moveReg2Reg(opBlock, opI, virtualReg,
opVal.getAllocatedRegNum(), dataSize);
}
// Save that register value to the stack of the TARGET REG
saveVirtRegToStack(opBlock, opI, virtualReg, physReg);
}
// make regs available to other instructions
clearAllRegs();
}
// really delete the PHI instruction now!
@ -304,9 +284,6 @@ void RegAllocSimple::EliminatePHINodes(MachineBasicBlock &MBB) {
void RegAllocSimple::AllocateBasicBlock(MachineBasicBlock &MBB) {
// Handle PHI instructions specially: add moves to each pred block
EliminatePHINodes(MBB);
// loop over each instruction
for (MachineBasicBlock::iterator I = MBB.begin(); I != MBB.end(); ++I) {
// Made to combat the incorrect allocation of r2 = add r1, r1
@ -366,6 +343,12 @@ bool RegAllocSimple::runOnMachineFunction(MachineFunction &Fn) {
DEBUG(std::cerr << "Machine Function " << "\n");
MF = &Fn;
// First pass: eliminate PHI instructions by inserting copies into predecessor
// blocks.
for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
MBB != MBBe; ++MBB)
EliminatePHINodes(*MBB);
// Loop over all of the basic blocks, eliminating virtual register references
for (MachineFunction::iterator MBB = Fn.begin(), MBBe = Fn.end();
MBB != MBBe; ++MBB)