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change machinelicm to use MachineInstr::isSafeToMove. No

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intended functionality change.

The avoidance of hoistiing implicitdef seems wrong though.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108109 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-07-12 00:00:35 +00:00
parent 68feb22ad8
commit 7791080151
1 changed files with 8 additions and 18 deletions
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26
lib/CodeGen/MachineLICM.cpp
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@ -127,8 +127,8 @@ namespace {
void AddToLiveIns(unsigned Reg);
/// IsLICMCandidate - Returns true if the instruction may be a suitable
/// candidate for LICM. e.g. If the instruction is a call, then it's obviously
/// not safe to hoist it.
/// candidate for LICM. e.g. If the instruction is a call, then it's
/// obviously not safe to hoist it.
bool IsLICMCandidate(MachineInstr &I);
/// IsLoopInvariantInst - Returns true if the instruction is loop
@ -497,26 +497,16 @@ void MachineLICM::HoistRegion(MachineDomTreeNode *N) {
/// candidate for LICM. e.g. If the instruction is a call, then it's obviously
/// not safe to hoist it.
bool MachineLICM::IsLICMCandidate(MachineInstr &I) {
// It is not profitable to hoist implicitdefs. FIXME: Why not? what if they
// are an argument to some other otherwise-hoistable instruction?
if (I.isImplicitDef())
return false;
const TargetInstrDesc &TID = I.getDesc();
// Ignore stuff that we obviously can't hoist.
if (TID.mayStore() || TID.isCall() || TID.isTerminator() ||
TID.hasUnmodeledSideEffects())
// Check if it's safe to move the instruction.
bool DontMoveAcrossStore = true;
if (!I.isSafeToMove(TII, AA, DontMoveAcrossStore))
return 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 (!I.isInvariantLoad(AA))
// FIXME: we should be able to hoist loads with no other side effects if
// there are no other instructions which can change memory in this loop.
// This is a trivial form of alias analysis.
return false;
}
return true;
}