[clang] [Wunsafe-buffer-usage] Turn off unsafe-buffer warning for methods annotated with clang::unsafe_buffer_usage attribute (PR #125671)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Malavika Samak (malavikasamak)

<details>
<summary>Changes</summary>

Unsafe operation in methods that are already annotated with clang::unsafe_buffer_usage attribute, should not trigger a warning. This is because, the developer has already identified the method as unsafe and warning at every unsafe operation is redundant.

rdar://138644831

---
Full diff: https://github.com/llvm/llvm-project/pull/125671.diff


2 Files Affected:

- (modified) clang/lib/Sema/AnalysisBasedWarnings.cpp (+3) 
- (modified) clang/test/SemaCXX/warn-unsafe-buffer-usage-function-attr.cpp (+41-6) 


``````````diff
diff --git a/clang/lib/Sema/AnalysisBasedWarnings.cpp b/clang/lib/Sema/AnalysisBasedWarnings.cpp
index 589869d0186575..7111dfd523a101 100644
--- a/clang/lib/Sema/AnalysisBasedWarnings.cpp
+++ b/clang/lib/Sema/AnalysisBasedWarnings.cpp
@@ -2610,6 +2610,9 @@ void clang::sema::AnalysisBasedWarnings::IssueWarnings(
 
   // The Callback function that performs analyses:
   auto CallAnalyzers = [&](const Decl *Node) -> void {
+    if (isa<FunctionDecl>(Node) && Node->hasAttr<UnsafeBufferUsageAttr>())
+        return;
+
     // Perform unsafe buffer usage analysis:
     if (!Diags.isIgnored(diag::warn_unsafe_buffer_operation,
                          Node->getBeginLoc()) ||
diff --git a/clang/test/SemaCXX/warn-unsafe-buffer-usage-function-attr.cpp b/clang/test/SemaCXX/warn-unsafe-buffer-usage-function-attr.cpp
index 724d444638b57e..ef724acc761dbd 100644
--- a/clang/test/SemaCXX/warn-unsafe-buffer-usage-function-attr.cpp
+++ b/clang/test/SemaCXX/warn-unsafe-buffer-usage-function-attr.cpp
@@ -119,16 +119,15 @@ struct HoldsUnsafeMembers {
 
     [[clang::unsafe_buffer_usage]]
     HoldsUnsafeMembers(int i)
-        : FromCtor(i),  // expected-warning{{function introduces unsafe buffer manipulation}}
-          FromCtor2{i}  // expected-warning{{function introduces unsafe buffer manipulation}}
-    {}
+        : FromCtor(i),
+          FromCtor2{i} {}
 
     HoldsUnsafeMembers(float f)
         : HoldsUnsafeMembers(0) {}  // expected-warning{{function introduces unsafe buffer manipulation}}
 
     UnsafeMembers FromCtor;
     UnsafeMembers FromCtor2;
-    UnsafeMembers FromField{3};  // expected-warning 2{{function introduces unsafe buffer manipulation}}
+    UnsafeMembers FromField{3};  // expected-warning {{function introduces unsafe buffer manipulation}}
 };
 
 struct SubclassUnsafeMembers : public UnsafeMembers {
@@ -138,8 +137,7 @@ struct SubclassUnsafeMembers : public UnsafeMembers {
 
     [[clang::unsafe_buffer_usage]]
     SubclassUnsafeMembers(int i)
-        : UnsafeMembers(i)  // expected-warning{{function introduces unsafe buffer manipulation}}
-    {}
+        : UnsafeMembers(i){}
 };
 
 // https://github.com/llvm/llvm-project/issues/80482
@@ -245,3 +243,40 @@ struct AggregateViaDefaultInit {
 void testAggregateViaDefaultInit() {
     AggregateViaDefaultInit A;
 };
+
+struct A {
+  int arr[2];
+
+  [[clang::unsafe_buffer_usage]]
+  int *ptr;
+};
+
+namespace std{
+  template <typename T> class span {
+
+   T *elements;
+
+   public:
+
+   constexpr span(T *, unsigned){}
+
+   template<class Begin, class End>
+   constexpr span(Begin first, End last){}
+
+   constexpr T* data() const noexcept {
+     return elements;
+   }
+ };
+}
+
+[[clang::unsafe_buffer_usage]]
+void check_no_warnings(unsigned idx) {
+  int *arr = new int[20];
+
+  int k = arr[idx]; // no-warning
+
+  std::span<int> sp = {arr, 20}; // no-warning
+  A *ptr = reinterpret_cast<A*> (sp.data()); // no-warning
+  A a;
+  a.ptr = arr; // no-warning
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/125671