[clang] ad2fb01 - [clang][Interp] Fix dereferencing arrays with no offset applied

[Timm Bäder via cfe-commits]

Author: Timm Bäder
Date: 2023-01-25T11:21:31+01:00
New Revision: ad2fb01cb68dc17594d2a923da90f5e01e127cdf

URL: https://github.com/llvm/llvm-project/commit/ad2fb01cb68dc17594d2a923da90f5e01e127cdf
DIFF: https://github.com/llvm/llvm-project/commit/ad2fb01cb68dc17594d2a923da90f5e01e127cdf.diff

LOG: [clang][Interp] Fix dereferencing arrays with no offset applied

A pointer to an array and a pointer to the first element of the array
are not the same in the interpreter, so handle this specially in
deref().

Differential Revision: https://reviews.llvm.org/D137082

Added: 
    

Modified: 
    clang/lib/AST/Interp/Pointer.h
    clang/test/AST/Interp/arrays.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/AST/Interp/Pointer.h b/clang/lib/AST/Interp/Pointer.h
index 1462d01c24126..489884a256598 100644
--- a/clang/lib/AST/Interp/Pointer.h
+++ b/clang/lib/AST/Interp/Pointer.h
@@ -225,6 +225,10 @@ class Pointer {
     return Offset - Base - Adjust;
   }
 
+  /// Whether this array refers to an array, but not
+  /// to the first element.
+  bool isArrayRoot() const { return inArray() && Offset == Base; }
+
   /// Checks if the innermost field is an array.
   bool inArray() const { return getFieldDesc()->IsArray; }
   /// Checks if the structure is a primitive array.
@@ -306,6 +310,10 @@ class Pointer {
   /// Dereferences the pointer, if it's live.
   template <typename T> T &deref() const {
     assert(isLive() && "Invalid pointer");
+    if (isArrayRoot())
+      return *reinterpret_cast<T *>(Pointee->rawData() + Base +
+                                    sizeof(InitMap *));
+
     return *reinterpret_cast<T *>(Pointee->rawData() + Offset);
   }
 

diff  --git a/clang/test/AST/Interp/arrays.cpp b/clang/test/AST/Interp/arrays.cpp
index cd8d37442e089..3c0eaefeb7965 100644
--- a/clang/test/AST/Interp/arrays.cpp
+++ b/clang/test/AST/Interp/arrays.cpp
@@ -42,6 +42,21 @@ constexpr int getElement(const int *Arr, int index) {
   return *(Arr + index);
 }
 
+constexpr int derefPtr(const int *d) {
+  return *d;
+}
+static_assert(derefPtr(data) == 5, "");
+
+constexpr int storePtr() {
+  int b[] = {1,2,3,4};
+  int *c = b;
+
+  *c = 4;
+  return *c;
+}
+static_assert(storePtr() == 4, "");
+
+
 static_assert(getElement(data, 1) == 4, "");
 static_assert(getElement(data, 4) == 1, "");