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For now, only hoist re-materilizable instructions. LICM will increase register pressure. We want to avoid spilling more instructions if it's possible.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@63725 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng 2009-02-04 07:17:49 +00:00
parent fb3dcf875b
commit 9b61f33351
1 changed files with 11 additions and 2 deletions
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13
lib/CodeGen/MachineLICM.cpp
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@ -186,18 +186,27 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
if (TID.mayStore() || TID.isCall() || TID.isTerminator() ||
TID.hasUnmodeledSideEffects())
return false;
bool isInvLoad = false;
if (TID.mayLoad()) {
// Okay, this instruction does a load. As a refinement, we allow the target
// to decide whether the loaded value is actually a constant. If so, we can
// actually use it as a load.
if (!TII->isInvariantLoad(&I))
isInvLoad = TII->isInvariantLoad(&I);
if (!isInvLoad)
// FIXME: we should be able to sink loads with no other side effects if
// there is nothing that can change memory from here until the end of
// block. This is a trivial form of alias analysis.
return false;
}
// FIXME: For now, only hoist re-materilizable instructions. LICM will
// increase register pressure. We want to make sure it doesn't increase
// spilling.
if (!isInvLoad && (!TID.isRematerializable() ||
!TII->isTriviallyReMaterializable(&I)))
return false;
DEBUG({
DOUT << "--- Checking if we can hoist " << I;
if (I.getDesc().getImplicitUses()) {