[llvm] [NFC] Address cppcheck legacyUninitvar (PR #175417)

[Konrad Kleine via llvm-commits]

https://github.com/kwk updated https://github.com/llvm/llvm-project/pull/175417

>From d38253a1ca0d70b6b58ff659d5dbc31a1d89ed6d Mon Sep 17 00:00:00 2001
From: Konrad Kleine <kkleine at redhat.com>
Date: Sun, 11 Jan 2026 09:11:09 +0100
Subject: [PATCH] [NFC] Suppress false-positive cppcheck legacyUninitvar in
 SaturatingAdd

Suppress this false-positive

```
 Error: CPPCHECK_WARNING (CWE-457): [#def65]
 llvm-project-21.1.8.src/llvm/include/llvm/Support/MathExtras.h:620: error[legacyUninitvar]: Uninitialized variable: Dummy
 #  618|   SaturatingAdd(T X, T Y, bool *ResultOverflowed = nullptr) {
 #  619|     bool Dummy;
 #  620|->   bool &Overflowed = ResultOverflowed ? *ResultOverflowed : Dummy;
 #  621|     // Hacker's Delight, p. 29
 #  622|     T Z = X + Y;
```

(Source: https://svashisht.fedorapeople.org/openscanhub/mass-scans/f44-08-Jan-2026/llvm-21.1.8-1.fc44/scan-results.html#def65)

The `Overflowed` variable is first written to.
That means the initial value in `Dummy` doesn't
matter and therfore this is a false-positive.
---
 llvm/include/llvm/Support/MathExtras.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/llvm/include/llvm/Support/MathExtras.h b/llvm/include/llvm/Support/MathExtras.h
index 0a253efc2abcb..0d63b2f8f6d62 100644
--- a/llvm/include/llvm/Support/MathExtras.h
+++ b/llvm/include/llvm/Support/MathExtras.h
@@ -608,6 +608,7 @@ template <typename T>
 std::enable_if_t<std::is_unsigned_v<T>, T>
 SaturatingAdd(T X, T Y, bool *ResultOverflowed = nullptr) {
   bool Dummy;
+  // cppcheck-suppress legacyUninitvar
   bool &Overflowed = ResultOverflowed ? *ResultOverflowed : Dummy;
   // Hacker's Delight, p. 29
   T Z = X + Y;