[clang] [clang] SemaFunctionEffects: When verifying a function, ignore any trailing 'requires' clause. (PR #114266)
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Wed Oct 30 10:07:26 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Doug Wyatt (dougsonos)
<details>
<summary>Changes</summary>
Clearly there's an omission here, that a trailing `requires` clause in a called function is being subject to effect analysis.
But despite many hours of effort I haven't been able to create a self-contained reproducer. My best effort:
```c++
#include <valarray>
#include <type_traits>
#include <expected>
template <class _Tp, _Tp __v>
struct integral_constant {
static constexpr _Tp value = __v;
typedef _Tp value_type;
typedef integral_constant type;
constexpr operator value_type() const noexcept { return value; }
constexpr value_type operator()() const noexcept { return value; }
};
template <typename T>
struct IsInt : public integral_constant<bool, false> {};
template <>
struct IsInt<int> : public integral_constant<bool, true> {};
template <typename T>
inline constexpr bool IsInt_V = IsInt<T>::value;
template <typename T, typename E>
struct ExpectedLike {
ExpectedLike() = default;
constexpr ExpectedLike(const ExpectedLike&)
// requires(IsInt_V<T> && IsInt_V<E> && IsInt_V<T>)
requires(std::is_copy_constructible_v<T> && std::is_copy_constructible_v<E> && std::is_trivially_copy_constructible_v<T> &&
std::is_trivially_copy_constructible_v<E>)
= default;
};
void nb_xx() [[clang::nonblocking]]
{
ExpectedLike<int, int> a;
auto b = a;
// No warning. I don't know why.
std::expected<int, int> c;
std::expected<int, int> d = c;
// ^^ warning: function with 'nonblocking' attribute must not call non-'nonblocking' constructor 'std::expected<int, int>::expected' [-Wfunction-effects]
}
```
The two elements of the mystery are:
- why doesn't my `ExpectedLike<T, E>` copy constructor reproduce the behavior of `std::expected<T, E>`?
- why does reproduction with `std::expected` depend on the global `operator &&` in `<valarray>`?
I've verified that the change to SemaFunctionEffects fixes the issue, but I'd sure like to be able to construct a self-contained test.
---
Full diff: https://github.com/llvm/llvm-project/pull/114266.diff
1 Files Affected:
- (modified) clang/lib/Sema/SemaFunctionEffects.cpp (+10)
``````````diff
diff --git a/clang/lib/Sema/SemaFunctionEffects.cpp b/clang/lib/Sema/SemaFunctionEffects.cpp
index 3fa326db06ee41..f7ff8b92d8a929 100644
--- a/clang/lib/Sema/SemaFunctionEffects.cpp
+++ b/clang/lib/Sema/SemaFunctionEffects.cpp
@@ -971,6 +971,7 @@ class Analyzer {
PendingFunctionAnalysis &CurrentFunction;
CallableInfo &CurrentCaller;
ViolationSite VSite;
+ const Expr *TrailingRequiresClause = nullptr;
FunctionBodyASTVisitor(Analyzer &Outer,
PendingFunctionAnalysis &CurrentFunction,
@@ -985,6 +986,9 @@ class Analyzer {
if (auto *Dtor = dyn_cast<CXXDestructorDecl>(CurrentCaller.CDecl))
followDestructor(dyn_cast<CXXRecordDecl>(Dtor->getParent()), Dtor);
+ if (auto *FD = dyn_cast<FunctionDecl>(CurrentCaller.CDecl))
+ TrailingRequiresClause = FD->getTrailingRequiresClause();
+
// Do an AST traversal of the function/block body
TraverseDecl(const_cast<Decl *>(CurrentCaller.CDecl));
}
@@ -1259,6 +1263,12 @@ class Analyzer {
return true;
}
+ bool TraverseStmt(Stmt *Statement) {
+ if (Statement != TrailingRequiresClause)
+ return Base::TraverseStmt(Statement);
+ return true;
+ }
+
bool TraverseConstructorInitializer(CXXCtorInitializer *Init) {
ViolationSite PrevVS = VSite;
if (Init->isAnyMemberInitializer())
``````````
</details>
https://github.com/llvm/llvm-project/pull/114266
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