[PATCH] D144486: [Assignment Tracking] Initialise maps with exact required number of entries

[Orlando Cazalet-Hyams via Phabricator via llvm-commits]

Orlando created this revision.
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The required size is known - the `Join` map in both cases gets an entry for each variable from both input maps (union). This avoids the unnecessary cost of repeatedly growing the map.

This improves ReleaseLTO-g compile time for CTMark projects by an average of around 0.2%.


https://reviews.llvm.org/D144486

Files:
  llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp


Index: llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
===================================================================
--- llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
+++ llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
@@ -1612,7 +1612,7 @@
   // then adding LocKind::None elements for vars in A xor B. The latter part is
   // equivalent to performing join on elements with variables in A xor B with
   // LocKind::None (⊤) since join(x, ⊤) = ⊤.
-  LocMap Join;
+  LocMap Join(std::max(A.size(), B.size()));
   SmallVector<VariableID, 16> SymmetricDifference;
   // Insert the join of the elements with common vars into Join. Add the
   // remaining elements to into SymmetricDifference.
@@ -1703,7 +1703,7 @@
   // then adding LocKind::None elements for vars in A xor B. The latter part is
   // equivalent to performing join on elements with variables in A xor B with
   // Status::NoneOrPhi (⊤) since join(x, ⊤) = ⊤.
-  AssignmentMap Join;
+  AssignmentMap Join(std::max(A.size(), B.size()));
   SmallVector<VariableID, 16> SymmetricDifference;
   // Insert the join of the elements with common vars into Join. Add the
   // remaining elements to into SymmetricDifference.


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