[clang][bytecode] Consider unknown-size arrays in memcpy/memcmp (llvm#121462)

When emitting diagnostics for the number of elements.

Author: tbaederr

clang/lib/AST/ByteCode/InterpBuiltin.cpp

@@ -1871,7 +1871,9 @@ static bool interp__builtin_memcpy(InterpState &S, CodePtr OpPC,
   size_t RemainingDestElems;
   if (DestPtr.getFieldDesc()->isArray()) {
     DestElemType = DestPtr.getFieldDesc()->getElemQualType();
-    RemainingDestElems = (DestPtr.getNumElems() - DestPtr.getIndex());
+    RemainingDestElems = DestPtr.isUnknownSizeArray()
+                             ? 0
+                             : (DestPtr.getNumElems() - DestPtr.getIndex());
   } else {
     DestElemType = DestPtr.getType();
     RemainingDestElems = 1;
@@ -1890,7 +1892,9 @@ static bool interp__builtin_memcpy(InterpState &S, CodePtr OpPC,
   size_t RemainingSrcElems;
   if (SrcPtr.getFieldDesc()->isArray()) {
     SrcElemType = SrcPtr.getFieldDesc()->getElemQualType();
-    RemainingSrcElems = (SrcPtr.getNumElems() - SrcPtr.getIndex());
+    RemainingSrcElems = SrcPtr.isUnknownSizeArray()
+                            ? 0
+                            : (SrcPtr.getNumElems() - SrcPtr.getIndex());
   } else {
     SrcElemType = SrcPtr.getType();
     RemainingSrcElems = 1;

clang/test/AST/ByteCode/builtin-functions.cpp

@@ -1263,6 +1263,15 @@ namespace BuiltinMemcpy {
     return arr[0].ok() && arr[1].ok() && arr[2].ok();
   }
   static_assert(test_trivial());
+
+  // Check that an incomplete array is rejected.
+  constexpr int test_incomplete_array_type() { // both-error {{never produces a constant}}
+    extern int arr[];
+    __builtin_memmove(arr, arr, 4 * sizeof(arr[0]));
+    // both-note@-1 2{{'memmove' not supported: source is not a contiguous array of at least 4 elements of type 'int'}}
+    return arr[0] * 1000 + arr[1] * 100 + arr[2] * 10 + arr[3];
+  }
+  static_assert(test_incomplete_array_type() == 1234); // both-error {{constant}} both-note {{in call}}
 }
 
 namespace Memcmp {