[Sema] Avoid unnecessary copy on MultiLevelTemplateArgumentList. NFC

[zyn0217]

We don't modify the MLTAL parameter in SetupConstraintScope, and it is better if we don't copy the 120-byte object each time we call the function.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

Changes

We don't modify the MLTAL parameter in SetupConstraintScope, and it is better if we don't copy the 120-byte object each time we call the function.

---

Full diff: https://github.com/llvm/llvm-project/pull/84459.diff

2 Files Affected:

• (modified) clang/include/clang/Sema/Sema.h (+6-4)
• (modified) clang/lib/Sema/SemaConcept.cpp (+2-1)

diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 592c7871a4a55d..2cac7e6ca08fad 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -11607,12 +11607,14 @@ class Sema final {
       LocalInstantiationScope &Scope,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
-  /// used by SetupConstraintCheckingTemplateArgumentsAndScope to recursively(in
+  /// Used by SetupConstraintCheckingTemplateArgumentsAndScope to recursively(in
   /// the case of lambdas) set up the LocalInstantiationScope of the current
   /// function.
-  bool SetupConstraintScope(
-      FunctionDecl *FD, std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
-      MultiLevelTemplateArgumentList MLTAL, LocalInstantiationScope &Scope);
+  bool
+  SetupConstraintScope(FunctionDecl *FD,
+                       std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
+                       const MultiLevelTemplateArgumentList &MLTAL,
+                       LocalInstantiationScope &Scope);
 
   /// Used during constraint checking, sets up the constraint template argument
   /// lists, and calls SetupConstraintScope to set up the
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index 2878e4d31ee8fe..a8e387e35fb4c9 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -586,7 +586,8 @@ bool Sema::addInstantiatedCapturesToScope(
 
 bool Sema::SetupConstraintScope(
     FunctionDecl *FD, std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
-    MultiLevelTemplateArgumentList MLTAL, LocalInstantiationScope &Scope) {
+    const MultiLevelTemplateArgumentList &MLTAL,
+    LocalInstantiationScope &Scope) {
   if (FD->isTemplateInstantiation() && FD->getPrimaryTemplate()) {
     FunctionTemplateDecl *PrimaryTemplate = FD->getPrimaryTemplate();
     InstantiatingTemplate Inst(

[Endilll]

Changes to Sema.h look good to me.

[erichkeane]

Ah, this used to be a really small class, at one point it was an unsigned plus a handful of array-refs, so it made sense to pass by value. It seems to have grown a decent bit to the point that pass-by-const-ref now makes sense.

[zyn0217]

Thanks. That explains now :)

[erichkeane]

Thanks. That explains now :)

No problem! Feel free to change a bunch of them, I'm sure we pass by copy quite a bit, I chased out many of them a while back, but I'm sure i didnt get them all.