Disable unreachable-code diagnostic on speficic constants/comparison #241751

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2. Andarwinux

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   clang:frontendLanguage frontend issues, e.g. anything involving "Sema"Language frontend issues, e.g. anything involving "Sema"

   clang:diagnosticsNew/improved warning or error message in Clang, but not in clang-tidy or static analyzerNew/improved warning or error message in Clang, but not in clang-tidy or static analyzer

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3. Andarwinux

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   Feature

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4. llvmorg-github-actions commented on Nov 12, 2026

   

   llvmorg-github-actionsBot

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   @llvm/issue-subscribers-clang-frontend

   Author: Federico Kircheis (fekir)

   Details

   I have following pattern

   // generated at configure time
   // depends on platform/compiler flags
   enum class platform{
       windows, debian, bsd, android, ...
       current = windows,
   };
   
   
   void foo();
   void bar();
   
   void baz1(bool condition){
       if(platform::current != platform::windows && condition){
           foo();
       } else if (!condition) {
           bar();
       }
   }

   but with -Wunreachable-code, clang diagnoses

   <source>:16:9: warning: code will never be executed [-Wunreachable-code]
      16 |         foo();
         |         ^~~
   <source>:15:50: warning: code will never be executed [-Wunreachable-code]
      15 |     if(platform::current != platform::windows && condition){
         |                                                  ^~~~~~~~~
   

   Note that (currently) the warning is not triggered for a switch statement, but transforming an if to a switch is error-prone, and does in general not improve the legibility.

   void baz2(bool condition){
       switch(platform::current){
           case platform::windows: if(!condition) bar(); break;
           default: if(condition) foo(); else bar(); break;
       }
   }

   It is possible to suppress the warning locally with a pragma, but adding such pragmato every if-statement is repetitive and error-prone.

   Is there a way to tell clang that the constant value platform::current depends on the compiler settings, and branches that depend on it are not necessarily dead?

   live example: https://compiler-explorer.com/z/Y7455nzYW
5. frederick-vs-ja

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6. EugeneZelenko

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   clang:frontendLanguage frontend issues, e.g. anything involving "Sema"Language frontend issues, e.g. anything involving "Sema"

   on Nov 12, 2026