https://github.com/MitraGulla created https://github.com/llvm/llvm-project/pull/235457
This fixes an unexpected `-Wfunction-effects` warning that occurs when Clang analyzes a template's dependent default argument, even though the caller provides the argument explicitly. Added a regression test for the reported issue and tests covering explicit and implicit arguments and other template default-argument cases. ## LLM usage LLM was used to help understand the issue, and finding relevant code part. The implementation and test changes were reviewed and tested locally. >From 838ab1bb5e68a53672f2b00b30ee307bc371cf68 Mon Sep 17 00:00:00 2001 From: MitraGulla <[email protected]> Date: Sun, 25 Oct 2026 20:02:05 +0530 Subject: [PATCH] [Clang] Fix nonblocking warning for dependent default arguments --- clang/lib/Sema/SemaFunctionEffects.cpp | 8 +++ .../Sema/attr-nonblocking-constraints.cpp | 52 +++++++++++++++++++ 2 files changed, 60 insertions(+) diff --git a/clang/lib/Sema/SemaFunctionEffects.cpp b/clang/lib/Sema/SemaFunctionEffects.cpp index 975281175aebb4..ef92e0c8b3ec47 100644 --- a/clang/lib/Sema/SemaFunctionEffects.cpp +++ b/clang/lib/Sema/SemaFunctionEffects.cpp @@ -1342,6 +1342,14 @@ class Analyzer { return Result; } + bool TraverseParmVarDecl(ParmVarDecl *D) override { + // Uninstantiated default arguments are dependent expressions that cannot + // be analyzed for function effects without producing incorrect warnings. + if (D->hasUninstantiatedDefaultArg()) + return true; + return DynamicRecursiveASTVisitor::TraverseParmVarDecl(D); + } + bool TraverseLambdaExpr(LambdaExpr *Lambda) override { // We override this so as to be able to skip traversal of the lambda's // body. We have to explicitly traverse the captures. Why not return diff --git a/clang/test/Sema/attr-nonblocking-constraints.cpp b/clang/test/Sema/attr-nonblocking-constraints.cpp index 400057768523c5..55aa3cfde11bc3 100644 --- a/clang/test/Sema/attr-nonblocking-constraints.cpp +++ b/clang/test/Sema/attr-nonblocking-constraints.cpp @@ -380,6 +380,58 @@ void nb21() [[clang::nonblocking]] { void nb22(int param = badForDefaultArg()) [[clang::nonblocking]] { // expected-warning {{function with 'nonblocking' attribute must not call non-'nonblocking' function 'badForDefaultArg'}} } + // Template default arguments + template <typename T> + int tmplDefaultSafe() noexcept [[clang::nonblocking]] { + return 0; + } + + template <typename T> + auto tmplDefault(T a = tmplDefaultSafe<T>()) noexcept [[clang::nonblocking]] { + return a; + } + + void testTmplDefaultExplicit(int x) [[clang::nonblocking]] { + tmplDefault(x); + } + + void testTmplDefaultImplicit() [[clang::nonblocking]] { + tmplDefault<int>(); + } + + int badForTmplDefaultArg(); // expected-note {{declaration cannot be inferred 'nonblocking' because it has no definition in this translation unit}} \ + // expected-note {{declaration cannot be inferred 'nonblocking' because it has no definition in this translation unit}} + + template <typename T> + auto tmplDefaultBad(T a = badForTmplDefaultArg()) noexcept [[clang::nonblocking]] { // expected-warning {{function with 'nonblocking' attribute must not call non-'nonblocking' function 'badForTmplDefaultArg'}} \ + // expected-warning {{function with 'nonblocking' attribute must not call non-'nonblocking' function 'badForTmplDefaultArg'}} + return a; + } + + void testTmplDefaultBadExplicit(int x) [[clang::nonblocking]] { + tmplDefaultBad(x); + } + + void testTmplDefaultBadImplicit() [[clang::nonblocking]] { + tmplDefaultBad<int>(); // expected-note {{in evaluating default argument here}} + } + + // An explicit argument must not trigger analysis of an unused dependent + // default argument. + template <typename T> + int f1() noexcept [[clang::nonblocking]] { + return 0; + } + + template <typename T> + auto f2(T a = f1<T>()) noexcept [[clang::nonblocking]] { + return a; + } + + void testDependentDefaultExplicit(int argc) [[clang::nonblocking]] { + f2(argc); + } + // Verify traversal of implicit code paths - constructors and destructors. struct Unsafe { static void problem1(); // expected-note {{declaration cannot be inferred 'nonblocking' because it has no definition in this translation unit}} _______________________________________________ cfe-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
