[lld] e205445 - [ELF] StringTableSection: Use DenseMap<CachedHashStringRef> to avoid redundant hash computation

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2022-01-16T21:02:05-08:00
New Revision: e20544543478b259eb09fa0a253d4fb1a5525d9e

URL: https://github.com/llvm/llvm-project/commit/e20544543478b259eb09fa0a253d4fb1a5525d9e
DIFF: https://github.com/llvm/llvm-project/commit/e20544543478b259eb09fa0a253d4fb1a5525d9e.diff

LOG: [ELF] StringTableSection: Use DenseMap<CachedHashStringRef> to avoid redundant hash computation

5~6% speedup when linking clang and chrome.

Added: 
    

Modified: 
    lld/ELF/SyntheticSections.cpp
    lld/ELF/SyntheticSections.h

Removed: 
    


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diff  --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index aef6434dca799..9944877acf6c7 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -1239,7 +1239,7 @@ StringTableSection::StringTableSection(StringRef name, bool dynamic)
 // them with some other string that happens to be the same.
 unsigned StringTableSection::addString(StringRef s, bool hashIt) {
   if (hashIt) {
-    auto r = stringMap.insert(std::make_pair(s, this->size));
+    auto r = stringMap.try_emplace(CachedHashStringRef(s), size);
     if (!r.second)
       return r.first->second;
   }

diff  --git a/lld/ELF/SyntheticSections.h b/lld/ELF/SyntheticSections.h
index 3090cf1aae147..6f8453288a8eb 100644
--- a/lld/ELF/SyntheticSections.h
+++ b/lld/ELF/SyntheticSections.h
@@ -421,7 +421,7 @@ class StringTableSection final : public SyntheticSection {
 
   uint64_t size = 0;
 
-  llvm::DenseMap<StringRef, unsigned> stringMap;
+  llvm::DenseMap<llvm::CachedHashStringRef, unsigned> stringMap;
   SmallVector<StringRef, 0> strings;
 };