[clang][bytecode] Fix crash when array index is past end of array in C (#165186)

Fixes #165090

Make sure to reject invalid array pointer offsets in C.

Co-authored-by: camc <[email protected]>

Author: camc

clang/lib/AST/ByteCode/Interp.h

@@ -2283,7 +2283,7 @@ std::optional<Pointer> OffsetHelper(InterpState &S, CodePtr OpPC,
     }
   }
 
-  if (Invalid && S.getLangOpts().CPlusPlus)
+  if (Invalid && (S.getLangOpts().CPlusPlus || Ptr.inArray()))
     return std::nullopt;
 
   // Offset is valid - compute it on unsigned.

clang/test/AST/ByteCode/c.c

@@ -381,3 +381,9 @@ static char foo_(a) // all-warning {{definition without a prototype}}
 static void bar_(void) {
   foo_(foo_(1));
 }
+
+void foo2(void*);
+void bar2(void) {
+  int a[2][3][4][5]; // all-note {{array 'a' declared here}}
+  foo2(&a[0][4]); // all-warning {{array index 4 is past the end of the array}}
+}