[scudo] Avoid deprecated-volatile warning in HybridMutex::delayLoop

[fabio-d]

That can prevent compilation with -Werror and -std=c++20:
mutex.h:63:7: error: increment of object of volatile-qualified type 'volatile u32' (aka 'volatile unsigned int') is deprecated [-Werror,-Wdeprecated-volatile]

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Changes

That can prevent compilation with -Werror and -std=c++20:
mutex.h:63:7: error: increment of object of volatile-qualified type 'volatile u32' (aka 'volatile unsigned int') is deprecated [-Werror,-Wdeprecated-volatile]

---

Full diff: https://github.com/llvm/llvm-project/pull/67135.diff

1 Files Affected:

• (modified) compiler-rt/lib/scudo/standalone/mutex.h (+6-2)

diff --git a/compiler-rt/lib/scudo/standalone/mutex.h b/compiler-rt/lib/scudo/standalone/mutex.h
index 38108397b1654bb..1563cdb3fb109cb 100644
--- a/compiler-rt/lib/scudo/standalone/mutex.h
+++ b/compiler-rt/lib/scudo/standalone/mutex.h
@@ -58,9 +58,13 @@ class CAPABILITY("mutex") HybridMutex {
     // are the fastest operations) so that we are unlikely to wait too long for
     // fast operations.
     constexpr u32 SpinTimes = 16;
-    volatile u32 V = 0;
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
+    volatile u32 V;
     for (u32 I = 0; I < SpinTimes; ++I)
-      ++V;
+      V = 0;
+#pragma GCC diagnostic pop
   }
 
   void assertHeldImpl();

[ChiaHungDuan]

Can you do it like,

        const u32 Tmp = V + 1;
        V = Tmp;

So that we don't need the pragma directive. I'll be replacing the use of volatile later

[ChiaHungDuan]

Thanks for the fix!