[clang] Optimize Cache Insertion with try_emplace for Reduced Lookups (PR #131402)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Ayush Pareek (ayushpareek2003)

<details>
<summary>Changes</summary>

for the functions- insertEntryForFilename() ,  insertRealPathForFilename()

Replaced `Cache.insert()` with `Cache.try_emplace()` to reduce redundant lookups
 Improved efficiency by avoiding unnecessary copying of values when the key already exists

---
Full diff: https://github.com/llvm/llvm-project/pull/131402.diff


1 Files Affected:

- (modified) clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h (+15-14) 


``````````diff
diff --git a/clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h b/clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h
index d12814e7c9253..a24ba86dae0ef 100644
--- a/clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h
+++ b/clang/include/clang/Tooling/DependencyScanning/DependencyScanningFilesystem.h
@@ -247,15 +247,16 @@ class DependencyScanningFilesystemLocalCache {
   insertEntryForFilename(StringRef Filename,
                          const CachedFileSystemEntry &Entry) {
     assert(llvm::sys::path::is_absolute_gnu(Filename));
-    auto [It, Inserted] = Cache.insert({Filename, {&Entry, nullptr}});
-    auto &[CachedEntry, CachedRealPath] = It->getValue();
-    if (!Inserted) {
-      // The file is already present in the local cache. If we got here, it only
-      // contains the real path. Let's make sure the entry is populated too.
-      assert((!CachedEntry && CachedRealPath) && "entry already present");
-      CachedEntry = &Entry;
-    }
-    return *CachedEntry;
+
+      auto &[CachedEntry, CachedRealPath] = Cache.try_emplace(
+          Filename, &Entry, nullptr).first->getValue();
+    
+      if (!CachedEntry) {
+        assert((!CachedEntry && CachedRealPath) && "entry already present");
+        CachedEntry = &Entry;
+      }
+    
+      return *CachedEntry;
   }
 
   /// Returns real path associated with the filename or nullptr if none is
@@ -272,14 +273,14 @@ class DependencyScanningFilesystemLocalCache {
   insertRealPathForFilename(StringRef Filename,
                             const CachedRealPath &RealPath) {
     assert(llvm::sys::path::is_absolute_gnu(Filename));
-    auto [It, Inserted] = Cache.insert({Filename, {nullptr, &RealPath}});
-    auto &[CachedEntry, CachedRealPath] = It->getValue();
-    if (!Inserted) {
-      // The file is already present in the local cache. If we got here, it only
-      // contains the entry. Let's make sure the real path is populated too.
+    auto &[CachedEntry, CachedRealPath] = Cache.try_emplace(
+          Filename, nullptr, &RealPath).first->getValue();
+    
+    if (!CachedRealPath) {
       assert((!CachedRealPath && CachedEntry) && "real path already present");
       CachedRealPath = &RealPath;
     }
+    
     return *CachedRealPath;
   }
 };

``````````

</details>


https://github.com/llvm/llvm-project/pull/131402