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Post-RA scheduler compile time fix. Quadratic computation of DAG node depth.

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The post-ra scheduler was explicitly updating the depth of a node's
successors after scheduling it, regardless of whether the successor
was ready. This is quadratic for DAGs with transitively redundant
edges. I simply removed the useless update of depth, which is lazilly
computed later.
Fixes <rdar://problem/9044332> compiler takes way too long to build TextInput.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@130992 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2011-05-06 17:09:08 +00:00
parent 31c5d05a26
commit 15ab3594eb
1 changed files with 10 additions and 4 deletions
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14
lib/CodeGen/PostRASchedulerList.cpp
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@ -540,10 +540,16 @@ void SchedulePostRATDList::ReleaseSucc(SUnit *SU, SDep *SuccEdge) {
#endif
--SuccSU->NumPredsLeft;
// Compute how many cycles it will be before this actually becomes
// available. This is the max of the start time of all predecessors plus
// their latencies.
SuccSU->setDepthToAtLeast(SU->getDepth() + SuccEdge->getLatency());
// Standard scheduler algorithms will recomute the depth of the successor
// here as such:
// SuccSU->setDepthToAtLeast(SU->getDepth() + SuccEdge->getLatency());
//
// However, we lazily compute node depth instead. Note that
// ScheduleNodeTopDown has already updated the depth of this node which causes
// all descendents to be marked dirty. Setting the successor depth explicitly
// here would cause depth to be recomputed for all its ancestors. If the
// successor is not yet ready (because of a transitively redundant edge) then
// this causes depth computation to be quadratic in the size of the DAG.
// If all the node's predecessors are scheduled, this node is ready
// to be scheduled. Ignore the special ExitSU node.