[clang] Revert "[clang][bytecode] Diagnose pointer subtractions of elements of different arrays" (PR #209969)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

Reverts llvm/llvm-project#<!-- -->209496

Breaks the new virtual-bases.cpp test

---
Full diff: https://github.com/llvm/llvm-project/pull/209969.diff


4 Files Affected:

- (modified) clang/lib/AST/ByteCode/Interp.h (+1-9) 
- (modified) clang/lib/AST/ByteCode/Pointer.cpp (+3-39) 
- (modified) clang/lib/AST/ByteCode/Pointer.h (+1-1) 
- (modified) clang/test/AST/ByteCode/cxx11.cpp (-19) 


``````````diff
diff --git a/clang/lib/AST/ByteCode/Interp.h b/clang/lib/AST/ByteCode/Interp.h
index 405f4a29ec982..2df52bbf460c7 100644
--- a/clang/lib/AST/ByteCode/Interp.h
+++ b/clang/lib/AST/ByteCode/Interp.h
@@ -2747,7 +2747,7 @@ inline bool SubPtr(InterpState &S, CodePtr OpPC, uint32_t ElemSize) {
     return false;
   }
 
-  if (!Pointer::hasSameBase(LHS, RHS)) {
+  if (!Pointer::hasSameBase(LHS, RHS) && S.getLangOpts().CPlusPlus) {
     S.FFDiag(S.Current->getSource(OpPC),
              diag::note_constexpr_pointer_arith_unspecified)
         << LHS.toDiagnosticString(S.getASTContext())
@@ -2771,14 +2771,6 @@ inline bool SubPtr(InterpState &S, CodePtr OpPC, uint32_t ElemSize) {
     return true;
   }
 
-  // C++11 [expr.add]p6:
-  //   Unless both pointers point to elements of the same array object, or
-  //   one past the last element of the array object, the behavior is
-  //   undefined.
-  if (LHS.isBlockPointer() && !Pointer::elemsOfSameArray(LHS, RHS))
-    S.CCEDiag(S.Current->getSource(OpPC),
-              diag::note_constexpr_pointer_subtraction_not_same_array);
-
   std::optional<size_t> VL = LHS.computeLayoutOffset(S.getASTContext());
   if (!VL)
     return false;
diff --git a/clang/lib/AST/ByteCode/Pointer.cpp b/clang/lib/AST/ByteCode/Pointer.cpp
index 243a2c9ea4b8f..1cd4370185209 100644
--- a/clang/lib/AST/ByteCode/Pointer.cpp
+++ b/clang/lib/AST/ByteCode/Pointer.cpp
@@ -815,45 +815,9 @@ bool Pointer::pointToSameBlock(const Pointer &A, const Pointer &B) {
   return A.block() == B.block();
 }
 
-bool Pointer::elemsOfSameArray(const Pointer &A, const Pointer &B) {
-  assert(hasSameBase(A, B));
-  assert(A.isBlockPointer());
-  assert(B.isBlockPointer());
-
-  if (A.BS.Base == B.BS.Base)
-    return true;
-
-  if (A.isBaseClass() || B.isBaseClass())
-    return false;
-
-  if (A.getField() || B.getField())
-    return false;
-
-  auto closestArray = [](const Pointer &P) -> PtrView {
-    if (P.isArrayRoot())
-      return P.view();
-
-    PtrView V = P.view();
-    if (V.isArrayElement() || V.isOnePastEnd())
-      V = V.expand().getArray();
-
-    if (P.isRoot())
-      return P.view();
-
-    while (!V.isRoot() && !V.getFieldDesc()->IsArray) {
-      if (V.isArrayElement()) {
-        V = V.expand().getArray();
-        break;
-      }
-      V = V.getBase();
-    }
-    return V;
-  };
-
-  if (closestArray(A) != closestArray(B))
-    return false;
-
-  return true;
+bool Pointer::hasSameArray(const Pointer &A, const Pointer &B) {
+  return hasSameBase(A, B) && A.BS.Base == B.BS.Base &&
+         A.getFieldDesc()->IsArray;
 }
 
 bool Pointer::pointsToLiteral() const {
diff --git a/clang/lib/AST/ByteCode/Pointer.h b/clang/lib/AST/ByteCode/Pointer.h
index c06347318dafa..417c28b46875a 100644
--- a/clang/lib/AST/ByteCode/Pointer.h
+++ b/clang/lib/AST/ByteCode/Pointer.h
@@ -999,7 +999,7 @@ class Pointer {
   /// Checks if two pointers are comparable.
   static bool hasSameBase(const Pointer &A, const Pointer &B);
   /// Checks if two pointers can be subtracted.
-  static bool elemsOfSameArray(const Pointer &A, const Pointer &B);
+  static bool hasSameArray(const Pointer &A, const Pointer &B);
   /// Checks if both given pointers point to the same block.
   static bool pointToSameBlock(const Pointer &A, const Pointer &B);
 
diff --git a/clang/test/AST/ByteCode/cxx11.cpp b/clang/test/AST/ByteCode/cxx11.cpp
index d920f0d4eb7f9..1e3668f8f2e99 100644
--- a/clang/test/AST/ByteCode/cxx11.cpp
+++ b/clang/test/AST/ByteCode/cxx11.cpp
@@ -482,22 +482,3 @@ namespace SubobjectCompare {
                                                     // both-note {{comparison of addresses of subobjects of different base classes has unspecified value}}
   static_assert((void*)(X*)&z != (void*)(Y*)&z, "");
 }
-
-namespace SubPtr {
-  struct A {};
-  struct B : A { int n; int m; };
-  B a[3][3];
-
-  constexpr int diff1 = &a[2] - &a[0];
-  constexpr int diff2 = &a[1][3] - &a[1][0];
-  constexpr int diff3 = &a[2][0] - &a[1][0]; // both-error {{constant expression}} \
-                                             // both-note {{subtracted pointers are not elements of the same array}}
-  // static_assert(&a[2][0] == &a[1][3], ""); FIXME
-  constexpr int diff4 = (&b + 1) - &b;
-  constexpr int diff5 = &a[1][2].n - &a[1][0].n; // both-error {{constant expression}} \
-                                                 // both-note {{subtracted pointers are not elements of the same array}}
-  constexpr int diff6 = &a[1][2].n - &a[1][2].n;
-  constexpr int diff7 = (A*)&a[0][1] - (A*)&a[0][0]; // both-error {{constant expression}} \
-                                                     // both-note {{subtracted pointers are not elements of the same array}}
-  constexpr auto diff8 = &a[1][2].n - (&a[1][2].n + 1);
-}

``````````

</details>


https://github.com/llvm/llvm-project/pull/209969