[PATCH] D137082: [clang][Interp] Fix dereferencing arrays with no offset applied

[Timm Bäder via Phabricator via cfe-commits]

tbaeder created this revision.
tbaeder added reviewers: aaron.ballman, erichkeane, tahonermann, shafik.
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There is a difference between a `Pointer` and a "`Pointer` to the first element of an array".


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D137082

Files:
  clang/lib/AST/Interp/Interp.h
  clang/test/AST/Interp/arrays.cpp


Index: clang/test/AST/Interp/arrays.cpp
===================================================================
--- clang/test/AST/Interp/arrays.cpp
+++ clang/test/AST/Interp/arrays.cpp
@@ -42,6 +42,12 @@
   return *(Arr + index);
 }
 
+constexpr int derefPtr(const int *d) {
+  return *d;
+}
+static_assert(derefPtr(data) == 5, "");
+
+
 static_assert(getElement(data, 1) == 4, "");
 static_assert(getElement(data, 4) == 1, "");
 
Index: clang/lib/AST/Interp/Interp.h
===================================================================
--- clang/lib/AST/Interp/Interp.h
+++ clang/lib/AST/Interp/Interp.h
@@ -949,7 +949,12 @@
   const Pointer &Ptr = S.Stk.peek<Pointer>();
   if (!CheckLoad(S, OpPC, Ptr))
     return false;
-  S.Stk.push<T>(Ptr.deref<T>());
+  // When getting the first value of an array, we need to offset to the
+  // first element.
+  if (Ptr.inArray() && Ptr.isRoot())
+    S.Stk.push<T>(Ptr.atIndex(0).deref<T>());
+  else
+    S.Stk.push<T>(Ptr.deref<T>());
   return true;
 }
 
@@ -958,7 +963,12 @@
   const Pointer &Ptr = S.Stk.pop<Pointer>();
   if (!CheckLoad(S, OpPC, Ptr))
     return false;
-  S.Stk.push<T>(Ptr.deref<T>());
+  // When getting the first value of an array, we need to offset to the
+  // first element.
+  if (Ptr.inArray() && Ptr.isRoot())
+    S.Stk.push<T>(Ptr.atIndex(0).deref<T>());
+  else
+    S.Stk.push<T>(Ptr.deref<T>());
   return true;
 }
 


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