[PATCH] D137488: [clang][Interp] Array initialization via string literal

[Tom Honermann via Phabricator via cfe-commits]

tahonermann added inline comments.


================
Comment at: clang/lib/AST/Interp/ByteCodeExprGen.cpp:1098-1099
+
+    unsigned N = SL->getLength();
+    for (size_t I = 0; I != NumElems; ++I) {
+      uint32_t CodePoint = I < N ? SL->getCodeUnit(I) : 0;
----------------
Aren't `N` and `NumElems` guaranteed to have the same value here? Both are derived from `SL`. The code seems to be written with the expectation that `NumElems` corresponds to the number of elements to be iniitialized in the target array.


================
Comment at: clang/lib/AST/Interp/ByteCodeExprGen.cpp:1100
+    for (size_t I = 0; I != NumElems; ++I) {
+      uint32_t CodePoint = I < N ? SL->getCodeUnit(I) : 0;
+      // TODO(Perf): 0 is implicit; we can just stop iterating at that point.
----------------
`CodePoint` should be `CodeUnit` here. `char` and friends all hold code units (in some cases, those code units may also constitute a code point).


================
Comment at: clang/test/AST/Interp/literals.cpp:354-359
+  constexpr char foo[12] = "abc";
+  static_assert(foo[0] == 'a', "");
+  static_assert(foo[1] == 'b', "");
+  static_assert(foo[2] == 'c', "");
+  static_assert(foo[3] == 0, "");
+  static_assert(foo[11] == 0, "");
----------------
aaron.ballman wrote:
> I'd like to see some tests for the other encodings, as well as a test with embedded null characters in the literal.
> 
> Testing a string literal that's longer than the array is something we should think about. That code is ill-formed in C++, so I don't think we can add a test for it yet, but it's only a warning in C.
I agree with Aaron's requests. Please also extend the test to include a `char` element that would be negative for a `signed` 8-bit `char`. Something like:
  constexpr char foo[12] = "abc\xff";
  ...
  #if defined(__CHAR_UNSIGNED__) || __CHAR_BIT__ > 8
  static_assert(foo[3] == 255, "");
  #else
  static_assert(foo[3] == -1, "");
  #endif

A couple of more tests to add:
- One where the string literal has the same length (including the implicit terminator) as the array; to ensure that the implicit terminator is properly accounted for.
- One where the target array size is deduced from the string literal; to ensure there are no dependencies on an explicit array size.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D137488/new/

https://reviews.llvm.org/D137488