[clang] Fix missing check for nullptr in CallExpr::getUnusedResultAttr

[Mick235711]

Fixes #117975, a regression introduced by #112521 due to me forgetting to check for nullptr before dereferencing in CallExpr::getUnusedResultAttr.
A regression test has been added as per the comments on the fixed issue.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Yihe Li (Mick235711)

Changes

Fixes #117975, a regression introduced by #112521 due to me forgetting to check for nullptr before dereferencing in CallExpr::getUnusedResultAttr.
A regression test has been added as per the comments on the fixed issue.

---

Full diff: https://github.com/llvm/llvm-project/pull/118636.diff

2 Files Affected:

• (modified) clang/lib/AST/Expr.cpp (+3-2)
• (modified) clang/test/SemaCXX/warn-unused-result.cpp (+9)

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index a4fb4d5a1f2ec4..286f02ded27196 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1619,8 +1619,9 @@ std::pair<const NamedDecl *, const Attr *>
 CallExpr::getUnusedResultAttr(const ASTContext &Ctx) const {
   // If the callee is marked nodiscard, return that attribute
   const Decl *D = getCalleeDecl();
-  if (const auto *A = D->getAttr<WarnUnusedResultAttr>())
-    return {nullptr, A};
+  if (D != nullptr)
+    if (const auto *A = D->getAttr<WarnUnusedResultAttr>())
+      return {nullptr, A};
 
   // If the return type is a struct, union, or enum that is marked nodiscard,
   // then return the return type attribute.
diff --git a/clang/test/SemaCXX/warn-unused-result.cpp b/clang/test/SemaCXX/warn-unused-result.cpp
index 682c500dc1d96d..5105f347db8b53 100644
--- a/clang/test/SemaCXX/warn-unused-result.cpp
+++ b/clang/test/SemaCXX/warn-unused-result.cpp
@@ -355,3 +355,12 @@ void use2() {
   (void)G{"Hello"};
 }
 } // namespace nodiscard_specialization
+
+namespace GH117975 {
+// Test for a regression for ICE in CallExpr::getUnusedResultAttr
+int f() { return 0; }
+void id_print_name() {
+  (int) // expected-warning {{expression result unused}}
+    ((int(*)())f)();
+}
+} // namespace GH117975

[cor3ntin]

LGTM

[shafik]

This was approved, do you need someone to merge this for you?

[Mick235711]

This was approved, do you need someone to merge this for you?

Yes, I do; I don't really have merge permissions. Thanks a lot for the helping hand.

[Mick235711]

Gentle ping @cor3ntin @Sirraide

[cor3ntin]

Sorry about that, it fell in the cracks. (in the future, feel free to ping every week if no one replies)