[PATCH] D83849: [TableGen] Reserve space in a vector to reduce the number of mallocs.

[Nadav Rotem via Phabricator via llvm-commits]

nadav created this revision.
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Reserve space in a vector to reduce the number of mallocs. The size of VTList is usually 1, but often 7. Push-backing into the vector in a loop triggers calls to reallocation of the vector. This happens hundreds of thousands of times in each tablegen instance.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D83849

Files:
  llvm/utils/TableGen/CodeGenDAGPatterns.cpp


Index: llvm/utils/TableGen/CodeGenDAGPatterns.cpp
===================================================================
--- llvm/utils/TableGen/CodeGenDAGPatterns.cpp
+++ llvm/utils/TableGen/CodeGenDAGPatterns.cpp
@@ -68,6 +68,7 @@
 // inference will apply to each mode separately.
 
 TypeSetByHwMode::TypeSetByHwMode(ArrayRef<ValueTypeByHwMode> VTList) {
+  AddrSpaces.reserve(VTList.size());
   for (const ValueTypeByHwMode &VVT : VTList) {
     insert(VVT);
     AddrSpaces.push_back(VVT.PtrAddrSpace);


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