[clang][bytecode] Fix delete[] dtor order (llvm#128411)

As always, call array dtors in reverse order.

Author: tbaederr

clang/lib/AST/ByteCode/Interp.cpp

@@ -1015,11 +1015,14 @@ static bool RunDestructors(InterpState &S, CodePtr OpPC, const Block *B) {
   assert(Desc->isRecord() || Desc->isCompositeArray());
 
   if (Desc->isCompositeArray()) {
+    unsigned N = Desc->getNumElems();
+    if (N == 0)
+      return true;
     const Descriptor *ElemDesc = Desc->ElemDesc;
     assert(ElemDesc->isRecord());
 
     Pointer RP(const_cast<Block *>(B));
-    for (unsigned I = 0; I != Desc->getNumElems(); ++I) {
+    for (int I = static_cast<int>(N) - 1; I >= 0; --I) {
       if (!runRecordDestructor(S, OpPC, RP.atIndex(I).narrow(), ElemDesc))
         return false;
     }

clang/test/AST/ByteCode/new-delete.cpp

@@ -942,6 +942,26 @@ namespace ArrayBaseCast {
   static_assert(test());
 }
 
+namespace PR45350 {
+  int q;
+  struct V { int n; int *p = &n; constexpr ~V() { *p = *p * 10 + n; }};
+  constexpr int f(int n) {
+    int k = 0;
+    V *p = new V[n];
+    for (int i = 0; i != n; ++i) {
+      if (p[i].p != &p[i].n) return -1;
+      p[i].n = i;
+      p[i].p = &k;
+    }
+    delete[] p;
+    return k;
+  }
+  // [expr.delete]p6:
+  //   In the case of an array, the elements will be destroyed in order of
+  //   decreasing address
+  static_assert(f(6) == 543210);
+}
+
 #else
 /// Make sure we reject this prior to C++20
 constexpr int a() { // both-error {{never produces a constant expression}}