[clang] [clang][Sema] Optimize ~SemaDiagnosticBuilder (PR #142252)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/142252

Call getDiagnosticLevel(), which is expensive, only if ShowCallStack is set.

Small gains:
https://llvm-compile-time-tracker.com/compare.php?from=843e362318e884991e517a54446b4faeacdad789&to=5cef0c18466318a426924b3c45f7abaaa8f6b535&stat=instructions:u

>From 25ba6bd099da9ea686850a47060f72a3cb6156d3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Fri, 30 May 2025 19:50:18 +0200
Subject: [PATCH] [clang][Sema] Optimize ~SemaDiagnosticBuilder

Call getDiagnosticLevel(), which is expensive, only if ShowCallStack is
set.

Small gains:
https://llvm-compile-time-tracker.com/compare.php?from=843e362318e884991e517a54446b4faeacdad789&to=5cef0c18466318a426924b3c45f7abaaa8f6b535&stat=instructions:u
---
 clang/lib/Sema/Sema.cpp | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 1901d19b14dfc..ff4c0d833e573 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -2062,11 +2062,14 @@ Sema::SemaDiagnosticBuilder::~SemaDiagnosticBuilder() {
   if (ImmediateDiag) {
     // Emit our diagnostic and, if it was a warning or error, output a callstack
     // if Fn isn't a priori known-emitted.
-    bool IsWarningOrError = S.getDiagnostics().getDiagnosticLevel(
-                                DiagID, Loc) >= DiagnosticsEngine::Warning;
     ImmediateDiag.reset(); // Emit the immediate diag.
-    if (IsWarningOrError && ShowCallStack)
-      emitCallStackNotes(S, Fn);
+
+    if (ShowCallStack) {
+      bool IsWarningOrError = S.getDiagnostics().getDiagnosticLevel(
+                                  DiagID, Loc) >= DiagnosticsEngine::Warning;
+      if (IsWarningOrError)
+        emitCallStackNotes(S, Fn);
+    }
   } else {
     assert((!PartialDiagId || ShowCallStack) &&
            "Must always show call stack for deferred diags.");