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If two-address def is dead and the instruction does not define other registers, and it doesn't produce side effects, just delete the instruction.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@65218 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2009-02-21 03:14:25 +00:00
parent d9fb712403
commit 28c7ce3fd4
2 changed files with 73 additions and 0 deletions
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30
lib/CodeGen/TwoAddressInstructionPass.cpp
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@ -53,6 +53,7 @@ STATISTIC(NumAggrCommuted , "Number of instructions aggressively commuted");
STATISTIC(NumConvertedTo3Addr, "Number of instructions promoted to 3-address");
STATISTIC(Num3AddrSunk, "Number of 3-address instructions sunk");
STATISTIC(NumReMats, "Number of instructions re-materialized");
STATISTIC(NumDeletes, "Number of dead instructions deleted");
namespace {
class VISIBILITY_HIDDEN TwoAddressInstructionPass
@ -371,6 +372,26 @@ TwoAddressInstructionPass::CommuteInstruction(MachineBasicBlock::iterator &mi,
return true;
}
/// isSafeToDelete - If the specified instruction does not produce any side
/// effects and all of its defs are dead, then it's safe to delete.
static bool isSafeToDelete(MachineInstr *MI, const TargetInstrInfo *TII) {
const TargetInstrDesc &TID = MI->getDesc();
if (TID.mayStore() || TID.isCall())
return false;
if (TID.isTerminator() || TID.hasUnmodeledSideEffects())
return false;
for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
MachineOperand &MO = MI->getOperand(i);
if (!MO.isReg() || !MO.isDef())
continue;
if (!MO.isDead())
return false;
}
return true;
}
/// runOnMachineFunction - Reduce two-address instructions to two operands.
///
bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
@ -450,6 +471,15 @@ bool TwoAddressInstructionPass::runOnMachineFunction(MachineFunction &MF) {
// allow us to coalesce A and B together, eliminating the copy we are
// about to insert.
if (!mi->killsRegister(regB)) {
// If regA is dead and the instruction can be deleted, just delete
// it so it doesn't clobber regB.
if (mi->getOperand(ti).isDead() && isSafeToDelete(mi, TII)) {
mbbi->erase(mi); // Nuke the old inst.
mi = nmi;
++NumDeletes;
break; // Done with this instruction.
}
// If this instruction is commutative, check to see if C dies. If
// so, swap the B and C operands. This makes the live ranges of A
// and C joinable.