[llvm-bugs] [Bug 33974] New: -Wunreachable-code/-Wunreachable-code-return is easily fooled by do{..}while(false) / macro

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=33974

            Bug ID: 33974
           Summary: -Wunreachable-code/-Wunreachable-code-return is easily
                    fooled by do{..}while(false) / macro
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: lebedev.ri at gmail.com
                CC: llvm-bugs at lists.llvm.org

Code:

void foo();
int main() {
    do {
        foo();
        __builtin_unreachable();
        foo();
    } while(false);

    foo();

    return 0;
}

Clang warns only on the second foo() call, but not the last one.
7 : <source>:7:9: warning: code will never be executed [-Wunreachable-code]
        foo();
        ^~~

Such do{stuff}while(false) pattern is used in macros to do some complicated
stuff.
And to add some more fun to it:

void foo();
#define macro() do {\
  foo(); \
  __builtin_unreachable(); \
  foo(); \
} while(false);

int main() {
    macro()

    foo();

    return 0;
}

clang issues no warning whatsoever for this...

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