[clang] [clang][bytecode] Diagnose comparisons of unrelated zero-sized pointers (PR #140695)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/140695.diff


2 Files Affected:

- (modified) clang/lib/AST/ByteCode/Interp.h (+8) 
- (modified) clang/test/AST/ByteCode/cxx11.cpp (+7) 


``````````diff
diff --git a/clang/lib/AST/ByteCode/Interp.h b/clang/lib/AST/ByteCode/Interp.h
index 9f1a6302eb856..23d3c088d571d 100644
--- a/clang/lib/AST/ByteCode/Interp.h
+++ b/clang/lib/AST/ByteCode/Interp.h
@@ -1135,6 +1135,14 @@ inline bool CmpHelperEQ<Pointer>(InterpState &S, CodePtr OpPC, CompareFn Fn) {
     }
   }
 
+  if (LHS.isUnknownSizeArray() && RHS.isUnknownSizeArray()) {
+    const SourceInfo &Loc = S.Current->getSource(OpPC);
+    S.FFDiag(Loc, diag::note_constexpr_pointer_comparison_zero_sized)
+        << LHS.toDiagnosticString(S.getASTContext())
+        << RHS.toDiagnosticString(S.getASTContext());
+    return false;
+  }
+
   S.Stk.push<BoolT>(BoolT::from(Fn(ComparisonCategoryResult::Unordered)));
   return true;
 }
diff --git a/clang/test/AST/ByteCode/cxx11.cpp b/clang/test/AST/ByteCode/cxx11.cpp
index 88e195c36b583..36a57001ab966 100644
--- a/clang/test/AST/ByteCode/cxx11.cpp
+++ b/clang/test/AST/ByteCode/cxx11.cpp
@@ -233,3 +233,10 @@ namespace IntToPtrCast {
   constexpr intptr_t i = f((intptr_t)&foo - 10); // both-error{{constexpr variable 'i' must be initialized by a constant expression}} \
                                                  // both-note{{reinterpret_cast}}
 }
+
+namespace ZeroSizeCmp {
+  extern void (*start[])();
+  extern void (*end[])();
+  static_assert(&start != &end, ""); // both-error {{constant expression}} \
+                                     // both-note {{comparison of pointers '&start' and '&end' to unrelated zero-sized objects}}
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/140695