[PATCH] D54355: Use is.constant intrinsic for __builtin_constant_p

[James Y Knight via Phabricator via cfe-commits]

jyknight added a comment.

In D54355#1328557 <https://reviews.llvm.org/D54355#1328557>, @void wrote:

> The issue is that "`n`" is expecting an immediate value, but the result of the ternary operator isn't calculated by the front-end, because it doesn't "know" that the evaluation of `__builtin_constant_p` shouldn't be delayed (it being compiled at `-O0`). I suspect that this issue will also happen with the "`i`" constraint.


Indeed. We _do_ actually already know that in clang too, however -- clang already knows that "n" requires an immediate, and does constant expression evaluation for it, e.g. to expand constexpr functions. Grep for "requiresImmediateConstant". I guess it's just not hooked up to the __b_c_p correctly, though.

(Note, as a workaround, you could use `|` instead of `||`, or put the expression as the value of an enumeration constant).


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  rC Clang

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