[llvm] [CodeGen][SDAG] Remove Combiner WorklistMap (PR #92900)
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Tue May 21 04:51:04 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-selectiondag
Author: None (aengelke)
<details>
<summary>Changes</summary>
DenseMap for pointer lookup is expensive, and this is only used for deduplication and index lookup. Instead, store the worklist index in the node itself.
This brings a substantial performance improvement, see [here (compile-time-tracker)](http://llvm-compile-time-tracker.com/compare.php?from=9d70975c7a72f3fa58d2d63090b92886dbf8a32b&to=13eff8c73d11595da9c01a0bb6580fea698aa3c9&stat=instructions:u).
---
Full diff: https://github.com/llvm/llvm-project/pull/92900.diff
2 Files Affected:
- (modified) llvm/include/llvm/CodeGen/SelectionDAGNodes.h (+9)
- (modified) llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (+12-16)
``````````diff
diff --git a/llvm/include/llvm/CodeGen/SelectionDAGNodes.h b/llvm/include/llvm/CodeGen/SelectionDAGNodes.h
index ac94c6099d080..7adda059647cb 100644
--- a/llvm/include/llvm/CodeGen/SelectionDAGNodes.h
+++ b/llvm/include/llvm/CodeGen/SelectionDAGNodes.h
@@ -619,6 +619,9 @@ END_TWO_BYTE_PACK()
/// Unique id per SDNode in the DAG.
int NodeId = -1;
+ /// Index in worklist of DAGCombiner, or -1.
+ int CombinerWorklistIndex = -1;
+
/// The values that are used by this operation.
SDUse *OperandList = nullptr;
@@ -747,6 +750,12 @@ END_TWO_BYTE_PACK()
/// Set unique node id.
void setNodeId(int Id) { NodeId = Id; }
+ /// Get worklist index for DAGCombiner
+ int getCombinerWorklistIndex() const { return CombinerWorklistIndex; }
+
+ /// Set worklist index for DAGCombiner
+ void setCombinerWorklistIndex(int Index) { CombinerWorklistIndex = Index; }
+
/// Return the node ordering.
unsigned getIROrder() const { return IROrder; }
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 8607b50175359..90c940e991835 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -170,16 +170,11 @@ namespace {
/// back and when processing we pop off of the back.
///
/// The worklist will not contain duplicates but may contain null entries
- /// due to nodes being deleted from the underlying DAG.
+ /// due to nodes being deleted from the underlying DAG. For fast lookup and
+ /// deduplication, the index of the node in this vector is stored in the
+ /// node in SDNode::CombinerWorklistIndex.
SmallVector<SDNode *, 64> Worklist;
- /// Mapping from an SDNode to its position on the worklist.
- ///
- /// This is used to find and remove nodes from the worklist (by nulling
- /// them) when they are deleted from the underlying DAG. It relies on
- /// stable indices of nodes within the worklist.
- DenseMap<SDNode *, unsigned> WorklistMap;
-
/// This records all nodes attempted to be added to the worklist since we
/// considered a new worklist entry. As we keep do not add duplicate nodes
/// in the worklist, this is different from the tail of the worklist.
@@ -238,10 +233,9 @@ namespace {
}
if (N) {
- bool GoodWorklistEntry = WorklistMap.erase(N);
- (void)GoodWorklistEntry;
- assert(GoodWorklistEntry &&
+ assert(N->getCombinerWorklistIndex() >= 0 &&
"Found a worklist entry without a corresponding map entry!");
+ N->setCombinerWorklistIndex(-1);
}
return N;
}
@@ -285,8 +279,10 @@ namespace {
if (IsCandidateForPruning)
ConsiderForPruning(N);
- if (WorklistMap.insert(std::make_pair(N, Worklist.size())).second)
+ if (N->getCombinerWorklistIndex() == -1) {
+ N->setCombinerWorklistIndex(Worklist.size());
Worklist.push_back(N);
+ }
}
/// Remove all instances of N from the worklist.
@@ -295,13 +291,13 @@ namespace {
PruningList.remove(N);
StoreRootCountMap.erase(N);
- auto It = WorklistMap.find(N);
- if (It == WorklistMap.end())
+ int WorklistIndex = N->getCombinerWorklistIndex();
+ if (WorklistIndex == -1)
return; // Not in the worklist.
// Null out the entry rather than erasing it to avoid a linear operation.
- Worklist[It->second] = nullptr;
- WorklistMap.erase(It);
+ Worklist[WorklistIndex] = nullptr;
+ N->setCombinerWorklistIndex(-1);
}
void deleteAndRecombine(SDNode *N);
``````````
</details>
https://github.com/llvm/llvm-project/pull/92900
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