[PATCH] D157052: [clang][deps] NFC: Speed up canonical context hash computation

[Jan Svoboda via Phabricator via cfe-commits]

jansvoboda11 created this revision.
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This patch makes use of the infrastructure established in D157046 <https://reviews.llvm.org/D157046> to speed up computation of the canonical context hash in the dependency scanner. This is somewhat hot code, since it's ran for all modules in the dependency graph of every TU.

I also tried an alternative approach that tried to avoid allocations as much as possible (essentially doing `HashBuilder.add(Arg.toStringRef(ArgVec))`), but that turned out to be slower than approach in this patch.

Note that this is not problematic in the same way command-line hashing used to be prior D143027 <https://reviews.llvm.org/D143027>. The lambda is now being called even for constant strings.

Depends on D157046 <https://reviews.llvm.org/D157046>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D157052

Files:
  clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp


Index: clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
===================================================================
--- clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
+++ clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
@@ -269,12 +269,13 @@
   HashBuilder.add(serialization::VERSION_MAJOR, serialization::VERSION_MINOR);
 
   // Hash the BuildInvocation without any input files.
-  SmallVector<const char *, 32> Args;
-  llvm::BumpPtrAllocator Alloc;
-  llvm::StringSaver Saver(Alloc);
-  CI.generateCC1CommandLine(
-      Args, [&](const Twine &Arg) { return Saver.save(Arg).data(); });
-  HashBuilder.addRange(Args);
+  SmallString<0> ArgVec;
+  ArgVec.reserve(4096);
+  CI.generateCC1CommandLine([&](const Twine &Arg) {
+    Arg.toVector(ArgVec);
+    ArgVec.push_back('\0');
+  });
+  HashBuilder.add(ArgVec);
 
   // Hash the module dependencies. These paths may differ even if the invocation
   // is identical if they depend on the contents of the files in the TU -- for


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