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Don't unconditionally suppress hoisting of instructions with implicit

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defs or uses. The regular def and use checking below covers them, and
can be more precise. It's safe to hoist an instruction with a dead
implicit def if the register isn't live into the loop header.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97352 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-02-28 00:08:44 +00:00
parent 53a50e2546
commit a363a9b71a
1 changed files with 4 additions and 26 deletions
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30
lib/CodeGen/MachineLICM.cpp
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@ -252,32 +252,6 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
return false;
}
DEBUG({
dbgs() << "--- Checking if we can hoist " << I;
if (I.getDesc().getImplicitUses()) {
dbgs() << " * Instruction has implicit uses:\n";
const TargetRegisterInfo *TRI = TM->getRegisterInfo();
for (const unsigned *ImpUses = I.getDesc().getImplicitUses();
*ImpUses; ++ImpUses)
dbgs() << " -> " << TRI->getName(*ImpUses) << "\n";
}
if (I.getDesc().getImplicitDefs()) {
dbgs() << " * Instruction has implicit defines:\n";
const TargetRegisterInfo *TRI = TM->getRegisterInfo();
for (const unsigned *ImpDefs = I.getDesc().getImplicitDefs();
*ImpDefs; ++ImpDefs)
dbgs() << " -> " << TRI->getName(*ImpDefs) << "\n";
}
});
if (I.getDesc().getImplicitDefs() || I.getDesc().getImplicitUses()) {
DEBUG(dbgs() << "Cannot hoist with implicit defines or uses\n");
return false;
}
// The instruction is loop invariant if all of its operands are.
for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
const MachineOperand &MO = I.getOperand(i);
@ -311,6 +285,10 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
} else if (!MO.isDead()) {
// A def that isn't dead. We can't move it.
return false;
} else if (CurLoop->getHeader()->isLiveIn(Reg)) {
// If the reg is live into the loop, we can't hoist an instruction
// which would clobber it.
return false;
}
}