<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/152561>152561</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            -Wunreachable-code-aggressive behaves strangely w/macros
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          pkasting
      </td>
    </tr>
</table>

<pre>
    Summary: `-Wunreachable-code-aggressive` triggers differently in the presence of macros, in some cases in bogus ways that seemingly can't be worked around.

Full description:

With `-Wunreachable-code-aggressive`, the following code somewhat-expectedly produces a warning that `f()` is unreachable:
```
true || f();
```
It also tells me to surround `true` with parens to silence, which indeed works.

Strangely, if this is instead a macro:
```
#define GOOD true
GOOD || f();
```
...then the warning is silent. I wouldn't have expected a difference since the two should be identical after the preprocessor runs.

Worse, however, is that if the macro has parens:
```
#define BAD (true)
BAD || f();
```
...then not only does the warning return, the note has disappeared, and there's no obvious way to silence the warning: Using `(BAD) || f();` or `(BAD || f());` or `BAD ? (void)0 : f();` all still warn. (Of course `f() || BAD;` would work, but calls `f()` in more scenarios, which may be undesirable.)

Sample code: https://godbolt.org/z/4ExznMTWr

This is problematic in Chromium, where we want to do things like
```
void f() {
  InitSomething(ON_PLATFORM_X() || HaveFeatureY());
}
```
...and `ON_PLATFORM_X()` is a macro set by the build system to be `(0)` or `(1)`. It might be possible to un-parenthesize what the macro evaluates to, but that seems very risky for widely-used low-level macros and IMO ought not to be necessary.
</pre>
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