[libc] Only perform MSAN unpoison in non-constexpr context.

[lntue]

No description provided.

[llvmbot]

@llvm/pr-subscribers-libc

Author: None (lntue)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/72299.diff

1 Files Affected:

• (modified) libc/src/__support/macros/sanitizer.h (+9-2)

diff --git a/libc/src/__support/macros/sanitizer.h b/libc/src/__support/macros/sanitizer.h
index 6989672b4839d20..fc66c2005c42de7 100644
--- a/libc/src/__support/macros/sanitizer.h
+++ b/libc/src/__support/macros/sanitizer.h
@@ -47,9 +47,16 @@
 // Functions to unpoison memory
 //-----------------------------------------------------------------------------
 
-#ifdef LIBC_HAVE_MEMORY_SANITIZER
+#if defined(LIBC_HAVE_MEMORY_SANITIZER) &&                                     \
+    LIBC_HAS_BUILTIN(__builtin_constant_p)
+// Only perform MSAN unpoison in non-constexpr context.
 #include <sanitizer/msan_interface.h>
-#define MSAN_UNPOISON(addr, size) __msan_unpoison(addr, size)
+#define MSAN_UNPOISON(addr, size)                                              \
+  do {                                                                         \
+    if (!__builtin_constant_p(*addr)) {                                        \
+      __msan_unpoison(addr, size);                                             \
+    }                                                                          \
+  } while (0)
 #else
 #define MSAN_UNPOISON(ptr, size)
 #endif

[michaelrj-google]

LGTM