[clang] [clang][Basic] Optimize getDiagnosticSeverity() (PR #141950)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/141950

Try not to call getDiagInfo() as often and only do it if we really have to.

>From 1946e68dab09b4eec02a742e61d2928abd5fc60e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Thu, 29 May 2025 13:00:07 +0200
Subject: [PATCH] [clang][Basic] Optimize getDiagnosticSeverity()

Try not to call getDiagInfo() as often and only do it if we really have
to.
---
 clang/lib/Basic/DiagnosticIDs.cpp | 36 ++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 15 deletions(-)

diff --git a/clang/lib/Basic/DiagnosticIDs.cpp b/clang/lib/Basic/DiagnosticIDs.cpp
index f01ff4df84e6a..ae1484519e812 100644
--- a/clang/lib/Basic/DiagnosticIDs.cpp
+++ b/clang/lib/Basic/DiagnosticIDs.cpp
@@ -543,26 +543,32 @@ DiagnosticIDs::getDiagnosticSeverity(unsigned DiagID, SourceLocation Loc,
     return Result;
 
   const auto &SM = Diag.getSourceManager();
-
-  bool ShowInSystemHeader =
-      IsCustomDiag
-          ? CustomDiagInfo->getDescription(DiagID).ShouldShowInSystemHeader()
-          : !GetDiagInfo(DiagID) || GetDiagInfo(DiagID)->WarnShowInSystemHeader;
-
   // If we are in a system header, we ignore it. We look at the diagnostic class
   // because we also want to ignore extensions and warnings in -Werror and
   // -pedantic-errors modes, which *map* warnings/extensions to errors.
-  if (State->SuppressSystemWarnings && !ShowInSystemHeader && Loc.isValid() &&
-      SM.isInSystemHeader(SM.getExpansionLoc(Loc)))
-    return diag::Severity::Ignored;
-
+  if (State->SuppressSystemWarnings && Loc.isValid() &&
+      SM.isInSystemHeader(SM.getExpansionLoc(Loc))) {
+    bool ShowInSystemHeader = false;
+    if (IsCustomDiag)
+      ShowInSystemHeader =
+          CustomDiagInfo->getDescription(DiagID).ShouldShowInSystemHeader();
+    else if (const StaticDiagInfoRec *Rec = GetDiagInfo(DiagID))
+      ShowInSystemHeader = Rec->WarnShowInSystemHeader;
+
+    if (!ShowInSystemHeader)
+      return diag::Severity::Ignored;
+  }
   // We also ignore warnings due to system macros
-  bool ShowInSystemMacro =
-      !GetDiagInfo(DiagID) || GetDiagInfo(DiagID)->WarnShowInSystemMacro;
-  if (State->SuppressSystemWarnings && !ShowInSystemMacro && Loc.isValid() &&
-      SM.isInSystemMacro(Loc))
-    return diag::Severity::Ignored;
+  if (State->SuppressSystemWarnings && Loc.isValid() &&
+      SM.isInSystemMacro(Loc)) {
+
+    bool ShowInSystemMacro = false;
+    if (const StaticDiagInfoRec *Rec = GetDiagInfo(DiagID))
+      ShowInSystemMacro = Rec->WarnShowInSystemMacro;
 
+    if (!ShowInSystemMacro)
+      return diag::Severity::Ignored;
+  }
   // Clang-diagnostics pragmas always take precedence over suppression mapping.
   if (!Mapping.isPragma() && Diag.isSuppressedViaMapping(DiagID, Loc))
     return diag::Severity::Ignored;