[clang] e830d88 - [UnsafeBufferUsage] Check for uninstantiated default arguments to prevent crash. (#188817)

[via cfe-commits]

Author: Zequan Wu
Date: 2026-03-26T14:50:28-07:00
New Revision: e830d88e8ae5f44a97cc76136a0a4e83aa9157c0

URL: https://github.com/llvm/llvm-project/commit/e830d88e8ae5f44a97cc76136a0a4e83aa9157c0
DIFF: https://github.com/llvm/llvm-project/commit/e830d88e8ae5f44a97cc76136a0a4e83aa9157c0.diff

LOG: [UnsafeBufferUsage] Check for uninstantiated default arguments to prevent crash. (#188817)

Fix a crash introduced by
https://github.com/llvm/llvm-project/pull/184899

The -Wunsafe-buffer-usage analysis was crashing when it encountered a
template function with a default argument that hadn't been instantiated
yet. This occurred in populateStmtsForFindingGadgets when it attempted
to access the default argument of each parameter.

This fix adds a check to ensure the default argument is instantiated
before attempting to access it.

Assisted-by: Gemini

Added: 
    clang/test/SemaCXX/warn-unsafe-buffer-usage-default-arg-uninstantiated-crash.cpp

Modified: 
    clang/lib/Analysis/UnsafeBufferUsage.cpp

Removed: 
    


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diff  --git a/clang/lib/Analysis/UnsafeBufferUsage.cpp b/clang/lib/Analysis/UnsafeBufferUsage.cpp
index 5a9241acbee36..c44a42dc93c13 100644
--- a/clang/lib/Analysis/UnsafeBufferUsage.cpp
+++ b/clang/lib/Analysis/UnsafeBufferUsage.cpp
@@ -2960,7 +2960,8 @@ static void populateStmtsForFindingGadgets(SmallVector<const Stmt *> &Stmts,
   if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
     AddStmt(FD->getBody());
     for (const auto *PD : FD->parameters())
-      AddStmt(PD->getDefaultArg());
+      if (PD->hasDefaultArg() && !PD->hasUninstantiatedDefaultArg())
+        AddStmt(PD->getDefaultArg());
     if (const auto *CtorD = dyn_cast<CXXConstructorDecl>(FD))
       llvm::append_range(
           Stmts, llvm::map_range(CtorD->inits(),

diff  --git a/clang/test/SemaCXX/warn-unsafe-buffer-usage-default-arg-uninstantiated-crash.cpp b/clang/test/SemaCXX/warn-unsafe-buffer-usage-default-arg-uninstantiated-crash.cpp
new file mode 100644
index 0000000000000..03bf427869484
--- /dev/null
+++ b/clang/test/SemaCXX/warn-unsafe-buffer-usage-default-arg-uninstantiated-crash.cpp
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -Wunsafe-buffer-usage -std=c++23 %s -verify
+
+// expected-no-diagnostics
+
+template <class _CharT> struct basic_string {
+  struct __rep {
+    __rep(int);
+  };
+  basic_string(_CharT, __rep = int()) {}
+};
+char16_t operators___str;
+decltype(sizeof(int)) operators___len;
+void operators() { basic_string(operators___str, operators___len); }