[clang] [clang][Frontend] Batch LangOptions context hashing (PR #203162)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: David Zbarsky (dzbarsky)

<details>
<summary>Changes</summary>

`CompilerInvocation::computeContextHash` currently expands 269 non-benign `LangOptions` into individual `HashBuilder::add` calls. This collects the values in an `unsigned` array and passes the array to `HashBuilder::addRangeElements`, which preserves the ordered native-endian bytes without adding an element count.

In a Release arm64 build, clangd decreases by 16,528 bytes unstripped and 16,544 bytes stripped.

Work towards #<!-- -->202616

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Full diff: https://github.com/llvm/llvm-project/pull/203162.diff


1 Files Affected:

- (modified) clang/lib/Frontend/CompilerInvocation.cpp (+13-6) 


``````````diff
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 47cdcad377d06..e1dd980db83cd 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -5215,15 +5215,22 @@ std::string CompilerInvocation::computeContextHash() const {
   HBuilder.add(serialization::VERSION_MAJOR, serialization::VERSION_MINOR);
 
   // Extend the signature with the language options
-  // FIXME: Replace with C++20 `using enum LangOptions::CompatibilityKind`.
-  using CK = LangOptions::CompatibilityKind;
+  const unsigned LanguageOptionValues[] = {
+#define HASH_LANGOPT_Benign(Value)
+#define HASH_LANGOPT_Compatible(Value) Value,
+#define HASH_LANGOPT_NotCompatible(Value) Value,
 #define LANGOPT(Name, Bits, Default, Compatibility, Description)               \
-  if constexpr (CK::Compatibility != CK::Benign)                               \
-    HBuilder.add(LangOpts->Name);
+  HASH_LANGOPT_##Compatibility(LangOpts->Name)
 #define ENUM_LANGOPT(Name, Type, Bits, Default, Compatibility, Description)    \
-  if constexpr (CK::Compatibility != CK::Benign)                               \
-    HBuilder.add(static_cast<unsigned>(LangOpts->get##Name()));
+  HASH_LANGOPT_##Compatibility(static_cast<unsigned>(LangOpts->get##Name()))
 #include "clang/Basic/LangOptions.def"
+  };
+#undef HASH_LANGOPT_Benign
+#undef HASH_LANGOPT_Compatible
+#undef HASH_LANGOPT_NotCompatible
+  // addRangeElements preserves the HBuilder.add sequence and excludes the
+  // LanguageOptionValues element count.
+  HBuilder.addRangeElements(LanguageOptionValues);
 
   HBuilder.addRange(getLangOpts().ModuleFeatures);
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/203162