eee944e7f9
This commit adds a new builtin, __builtin_bit_cast(T, v), which performs a bit_cast from a value v to a type T. This expression can be evaluated at compile time under specific circumstances. The compile time evaluation currently doesn't support bit-fields, but I'm planning on fixing this in a follow up (some of the logic for figuring this out is in CodeGen). I'm also planning follow-ups for supporting some more esoteric types that the constexpr evaluator supports, as well as extending __builtin_memcpy constexpr evaluation to use the same infrastructure. rdar://44987528 Differential revision: https://reviews.llvm.org/D62825 llvm-svn: 364954
40 lines
1.1 KiB
C++
40 lines
1.1 KiB
C++
// RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -triple x86_64-apple-macosx10.14.0 %s
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// RUN: %clang_cc1 -verify -std=c++2a -fsyntax-only -triple x86_64-apple-macosx10.14.0 %s -fno-signed-char
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#if !__has_builtin(__builtin_bit_cast)
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#error
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#endif
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template <class T, T v>
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T instantiate() {
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return __builtin_bit_cast(T, v);
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}
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int x = instantiate<int, 32>();
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struct secret_ctor {
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char member;
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private: secret_ctor() = default;
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};
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void test1() {
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secret_ctor c = __builtin_bit_cast(secret_ctor, (char)0);
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}
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void test2() {
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constexpr int i = 0;
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// expected-error@+1{{__builtin_bit_cast source size does not equal destination size (4 vs 1)}}
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constexpr char c = __builtin_bit_cast(char, i);
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}
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struct not_trivially_copyable {
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virtual void foo() {}
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};
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// expected-error@+1{{__builtin_bit_cast source type must be trivially copyable}}
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constexpr unsigned long ul = __builtin_bit_cast(unsigned long, not_trivially_copyable{});
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// expected-error@+1 {{__builtin_bit_cast destination type must be trivially copyable}}
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constexpr long us = __builtin_bit_cast(unsigned long &, 0L);
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