Recommit r129383. PreRA scheduler heuristic fixes: VRegCycle, TokenFactor latency.
Additional fixes:
Do something reasonable for subtargets with generic
itineraries by handle node latency the same as for an empty
itinerary. Now nodes default to unit latency unless an itinerary
explicitly specifies a zero cycle stage or it is a TokenFactor chain.
Original fixes:
UnitsSharePred was a source of randomness in the scheduler: node
priority depended on the queue data structure. I rewrote the recent
VRegCycle heuristics to completely replace the old heuristic without
any randomness. To make the ndoe latency adjustments work, I also
needed to do something a little more reasonable with TokenFactor. I
gave it zero latency to its consumers and always schedule it as low as
possible.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129421 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
index 24a1937..078533b 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
@@ -342,10 +342,6 @@
assert(N->getNodeId() == -1 && "Node already inserted!");
N->setNodeId(NodeSUnit->NodeNum);
- // Set isVRegCycle if the node operands are live into and value is live out
- // of a single block loop.
- InitVRegCycleFlag(NodeSUnit);
-
// Compute NumRegDefsLeft. This must be done before AddSchedEdges.
InitNumRegDefsLeft(NodeSUnit);
@@ -417,6 +413,10 @@
// If this is a ctrl dep, latency is 1.
unsigned OpLatency = isChain ? 1 : OpSU->Latency;
+ // Special-case TokenFactor chains as zero-latency.
+ if(isChain && OpN->getOpcode() == ISD::TokenFactor)
+ OpLatency = 0;
+
const SDep &dep = SDep(OpSU, isChain ? SDep::Order : SDep::Data,
OpLatency, PhysReg);
if (!isChain && !UnitLatencies) {
@@ -512,47 +512,6 @@
}
}
-// Set isVRegCycle if this node's single use is CopyToReg and its only active
-// data operands are CopyFromReg.
-//
-// This is only relevant for single-block loops, in which case the VRegCycle
-// node is likely an induction variable in which the operand and target virtual
-// registers should be coalesced (e.g. pre/post increment values). Setting the
-// isVRegCycle flag helps the scheduler prioritize other uses of the same
-// CopyFromReg so that this node becomes the virtual register "kill". This
-// avoids interference between the values live in and out of the block and
-// eliminates a copy inside the loop.
-void ScheduleDAGSDNodes::InitVRegCycleFlag(SUnit *SU) {
- if (!BB->isSuccessor(BB))
- return;
-
- SDNode *N = SU->getNode();
- if (N->getGluedNode())
- return;
-
- if (!N->hasOneUse() || N->use_begin()->getOpcode() != ISD::CopyToReg)
- return;
-
- bool FoundLiveIn = false;
- for (SDNode::op_iterator OI = N->op_begin(), E = N->op_end(); OI != E; ++OI) {
- EVT OpVT = OI->getValueType();
- assert(OpVT != MVT::Glue && "Glued nodes should be in same sunit!");
-
- if (OpVT == MVT::Other)
- continue; // ignore chain operands
-
- if (isPassiveNode(OI->getNode()))
- continue; // ignore constants and such
-
- if (OI->getNode()->getOpcode() != ISD::CopyFromReg)
- return;
-
- FoundLiveIn = true;
- }
- if (FoundLiveIn)
- SU->isVRegCycle = true;
-}
-
void ScheduleDAGSDNodes::InitNumRegDefsLeft(SUnit *SU) {
assert(SU->NumRegDefsLeft == 0 && "expect a new node");
for (RegDefIter I(SU, this); I.IsValid(); I.Advance()) {
@@ -562,6 +521,16 @@
}
void ScheduleDAGSDNodes::ComputeLatency(SUnit *SU) {
+ SDNode *N = SU->getNode();
+
+ // TokenFactor operands are considered zero latency, and some schedulers
+ // (e.g. Top-Down list) may rely on the fact that operand latency is nonzero
+ // whenever node latency is nonzero.
+ if (N && N->getOpcode() == ISD::TokenFactor) {
+ SU->Latency = 0;
+ return;
+ }
+
// Check to see if the scheduler cares about latencies.
if (ForceUnitLatencies()) {
SU->Latency = 1;
@@ -569,7 +538,6 @@
}
if (!InstrItins || InstrItins->isEmpty()) {
- SDNode *N = SU->getNode();
if (N && N->isMachineOpcode() &&
TII->isHighLatencyDef(N->getMachineOpcode()))
SU->Latency = HighLatencyCycles;