aaron.ballman added inline comments.
================
Comment at: clang/test/Sema/constant-builtins-ilogb.cpp:1
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+// expected-no-diagnostics
----------------
hubert.reinterpretcast wrote:
> There seems to be no C language test in the patch (although the builtin
> presumably is okay at least as part of arithmetic constant expressions).
>
> @aaron.ballman, what are your thoughts re: integer constant expression
> contexts? For example:
> ```
> struct C { int x : __builtin_ilogb(1. + 1.); };
> ```
WG14 adopted https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2713.htm for C2x
to clarify that implementations are not allowed to extend what they consider to
be an integer constant expression. The operand in this case is a function call
expression, which is not one of the permissible things in an ICE, so the
standard doesn't want us to make it one.
I believe that Clang's response to that paper is to implement it to the letter
rather than to the intent. e.g., issue a warning that a constant expression is
being folded into an ICE but otherwise accept the code. We have too many
situations already in which we fold a constant expression to an ICE and
changing that behavior would be observable (and a performance regression). So I
think it's fine for us to treat the builtin call as an ICE so long as we issue
a (pedantic) warning about folding it.
(FWIW, I don't think it qualifies as an arithmetic constant expression because
that also doesn't allow function call expressions. But we can extend the
definition of an arithmetic constant expression.)
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D136568/new/
https://reviews.llvm.org/D136568
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
