r359067 - [Builtins] Implement __builtin_is_constant_evaluated for use in C++2a
Richard Smith via cfe-commits
cfe-commits at lists.llvm.org
Thu Apr 25 14:31:28 PDT 2019
On Wed, 24 Apr 2019 at 19:28, Eric Fiselier via cfe-commits
<cfe-commits at lists.llvm.org> wrote:
> Do I just edit the HTML file directly?
> Or is it generated by something?
Just edit the HTML file directly.
> On Wed, Apr 24, 2019 at 3:35 PM Richard Smith <richard at metafoo.co.uk> wrote:
>>
>> Thanks! Can you update cxx_status.html to mark P0595R2 as done?
>>
>> On Tue, 23 Apr 2019 at 19:21, Eric Fiselier via cfe-commits
>> <cfe-commits at lists.llvm.org> wrote:
>> >
>> > Author: ericwf
>> > Date: Tue Apr 23 19:23:30 2019
>> > New Revision: 359067
>> >
>> > URL: http://llvm.org/viewvc/llvm-project?rev=359067&view=rev
>> > Log:
>> > [Builtins] Implement __builtin_is_constant_evaluated for use in C++2a
>> >
>> > Summary:
>> > This patch implements `__builtin_is_constant_evaluated` as specifier by [P0595R2](https://wg21.link/p0595r2). It is built on the back of Bill Wendling's work for `__builtin_constant_p()`.
>> >
>> > More tests to come, but early feedback is appreciated.
>> >
>> > I plan to implement warnings for common mis-usages like those belowe in a following patch:
>> > ```
>> > void foo(int x) {
>> > if constexpr (std::is_constant_evaluated())) { // condition is always `true`. Should use plain `if` instead.
>> > foo_constexpr(x);
>> > } else {
>> > foo_runtime(x);
>> > }
>> > }
>> > ```
>> >
>> >
>> >
>> > Reviewers: rsmith, MaskRay, bruno, void
>> >
>> > Reviewed By: rsmith
>> >
>> > Subscribers: dexonsmith, zoecarver, fdeazeve, kristina, cfe-commits
>> >
>> > Differential Revision: https://reviews.llvm.org/D55500
>> >
>> > Added:
>> > cfe/trunk/test/CodeGenCXX/builtin-is-constant-evaluated.cpp
>> > cfe/trunk/test/SemaCXX/builtin-is-constant-evaluated.cpp
>> > Modified:
>> > cfe/trunk/include/clang/Basic/Builtins.def
>> > cfe/trunk/lib/AST/ExprConstant.cpp
>> > cfe/trunk/lib/Basic/Builtins.cpp
>> > cfe/trunk/lib/CodeGen/CGDecl.cpp
>> > cfe/trunk/test/Sema/builtins.c
>> >
>> > Modified: cfe/trunk/include/clang/Basic/Builtins.def
>> > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Builtins.def?rev=359067&r1=359066&r2=359067&view=diff
>> > ==============================================================================
>> > --- cfe/trunk/include/clang/Basic/Builtins.def (original)
>> > +++ cfe/trunk/include/clang/Basic/Builtins.def Tue Apr 23 19:23:30 2019
>> > @@ -500,6 +500,7 @@ BUILTIN(__builtin_vsprintf, "ic*cC*a", "
>> > BUILTIN(__builtin_vsnprintf, "ic*zcC*a", "nFP:2:")
>> > BUILTIN(__builtin_thread_pointer, "v*", "nc")
>> > BUILTIN(__builtin_launder, "v*v*", "nt")
>> > +LANGBUILTIN(__builtin_is_constant_evaluated, "b", "n", CXX_LANG)
>> >
>> > // GCC exception builtins
>> > BUILTIN(__builtin_eh_return, "vzv*", "r") // FIXME: Takes intptr_t, not size_t!
>> >
>> > Modified: cfe/trunk/lib/AST/ExprConstant.cpp
>> > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ExprConstant.cpp?rev=359067&r1=359066&r2=359067&view=diff
>> > ==============================================================================
>> > --- cfe/trunk/lib/AST/ExprConstant.cpp (original)
>> > +++ cfe/trunk/lib/AST/ExprConstant.cpp Tue Apr 23 19:23:30 2019
>> > @@ -8279,6 +8279,9 @@ bool IntExprEvaluator::VisitBuiltinCallE
>> > return Success(false, E);
>> > }
>> >
>> > + case Builtin::BI__builtin_is_constant_evaluated:
>> > + return Success(Info.InConstantContext, E);
>> > +
>> > case Builtin::BI__builtin_ctz:
>> > case Builtin::BI__builtin_ctzl:
>> > case Builtin::BI__builtin_ctzll:
>> > @@ -11139,6 +11142,7 @@ bool Expr::EvaluateAsConstantExpr(EvalRe
>> > EvalInfo::EvaluationMode EM = EvalInfo::EM_ConstantExpression;
>> > EvalInfo Info(Ctx, Result, EM);
>> > Info.InConstantContext = true;
>> > +
>> > if (!::Evaluate(Result.Val, Info, this))
>> > return false;
>> >
>> >
>> > Modified: cfe/trunk/lib/Basic/Builtins.cpp
>> > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Basic/Builtins.cpp?rev=359067&r1=359066&r2=359067&view=diff
>> > ==============================================================================
>> > --- cfe/trunk/lib/Basic/Builtins.cpp (original)
>> > +++ cfe/trunk/lib/Basic/Builtins.cpp Tue Apr 23 19:23:30 2019
>> > @@ -75,9 +75,12 @@ bool Builtin::Context::builtinIsSupporte
>> > bool OclCUnsupported = !LangOpts.OpenCL &&
>> > (BuiltinInfo.Langs & ALL_OCLC_LANGUAGES);
>> > bool OpenMPUnsupported = !LangOpts.OpenMP && BuiltinInfo.Langs == OMP_LANG;
>> > + bool CPlusPlusUnsupported =
>> > + !LangOpts.CPlusPlus && BuiltinInfo.Langs == CXX_LANG;
>> > return !BuiltinsUnsupported && !MathBuiltinsUnsupported && !OclCUnsupported &&
>> > !OclC1Unsupported && !OclC2Unsupported && !OpenMPUnsupported &&
>> > - !GnuModeUnsupported && !MSModeUnsupported && !ObjCUnsupported;
>> > + !GnuModeUnsupported && !MSModeUnsupported && !ObjCUnsupported &&
>> > + !CPlusPlusUnsupported;
>> > }
>> >
>> > /// initializeBuiltins - Mark the identifiers for all the builtins with their
>> >
>> > Modified: cfe/trunk/lib/CodeGen/CGDecl.cpp
>> > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGDecl.cpp?rev=359067&r1=359066&r2=359067&view=diff
>> > ==============================================================================
>> > --- cfe/trunk/lib/CodeGen/CGDecl.cpp (original)
>> > +++ cfe/trunk/lib/CodeGen/CGDecl.cpp Tue Apr 23 19:23:30 2019
>> > @@ -1783,7 +1783,8 @@ void CodeGenFunction::EmitAutoVarInit(co
>> > }
>> >
>> > llvm::Constant *constant = nullptr;
>> > - if (emission.IsConstantAggregate || D.isConstexpr()) {
>> > + if (emission.IsConstantAggregate || D.isConstexpr() ||
>> > + D.isUsableInConstantExpressions(getContext())) {
>> > assert(!capturedByInit && "constant init contains a capturing block?");
>> > constant = ConstantEmitter(*this).tryEmitAbstractForInitializer(D);
>> > if (constant && trivialAutoVarInit !=
>> >
>> > Added: cfe/trunk/test/CodeGenCXX/builtin-is-constant-evaluated.cpp
>> > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/builtin-is-constant-evaluated.cpp?rev=359067&view=auto
>> > ==============================================================================
>> > --- cfe/trunk/test/CodeGenCXX/builtin-is-constant-evaluated.cpp (added)
>> > +++ cfe/trunk/test/CodeGenCXX/builtin-is-constant-evaluated.cpp Tue Apr 23 19:23:30 2019
>> > @@ -0,0 +1,133 @@
>> > +// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm %s -std=c++2a -o %t.ll
>> > +// RUN: FileCheck -check-prefix=CHECK-FN-CG -input-file=%t.ll %s
>> > +// RUN: FileCheck -check-prefix=CHECK-STATIC -input-file=%t.ll %s
>> > +// RUN: FileCheck -check-prefix=CHECK-DYN -input-file=%t.ll %s
>> > +// RUN: FileCheck -check-prefix=CHECK-ARR -input-file=%t.ll %s
>> > +// RUN: FileCheck -check-prefix=CHECK-FOLD -input-file=%t.ll %s
>> > +
>> > +using size_t = decltype(sizeof(int));
>> > +
>> > +#define CONSTINIT __attribute__((require_constant_initialization))
>> > +
>> > +extern "C" [[noreturn]] void BOOM();
>> > +extern "C" void OK();
>> > +extern "C" size_t RANDU();
>> > +
>> > +namespace std {
>> > +inline constexpr bool is_constant_evaluated() noexcept {
>> > + return __builtin_is_constant_evaluated();
>> > +}
>> > +} // namespace std
>> > +
>> > +// CHECK-FN-CG-LABEL: define zeroext i1 @_Z3foov()
>> > +// CHECK-FN-CG: ret i1 false
>> > +bool foo() {
>> > + return __builtin_is_constant_evaluated();
>> > +}
>> > +
>> > +// CHECK-FN-CG-LABEL: define linkonce_odr i32 @_Z1fv()
>> > +constexpr int f() {
>> > + // CHECK-FN-CG: store i32 13, i32* %n, align 4
>> > + // CHECK-FN-CG: store i32 17, i32* %m, align 4
>> > + // CHECK-FN-CG: %1 = load i32, i32* %m, align 4
>> > + // CHECK-FN-CG: %add = add nsw i32 %1, 13
>> > + // CHECK-FN-CG: ret i32 %add
>> > + const int n = __builtin_is_constant_evaluated() && std::is_constant_evaluated() ? 13 : 17; // n == 13
>> > + int m = __builtin_is_constant_evaluated() ? 13 : 17; // m might be 13 or 17 (see below)
>> > + char arr[n] = {}; // char[13]
>> > + return m + int(sizeof(arr));
>> > +}
>> > +
>> > +// CHECK-STATIC-DAG: @p = global i32 26,
>> > +CONSTINIT int p = f(); // f().m == 13; initialized to 26
>> > +// CHECK-STATIC-DAG: @p2 = global i32 26,
>> > +int p2 = f(); // same result without CONSTINIT
>> > +
>> > +// CHECK-DYN-LABEL: define internal void @__cxx_global_var_init()
>> > +// CHECK-DYN: %0 = load i32, i32* @p, align 4
>> > +// CHECK-DYN-NEXT: %call = call i32 @_Z1fv()
>> > +// CHECK-DYN-NEXT: %add = add nsw i32 %0, %call
>> > +// CHECK-DYN-NEXT: store i32 %add, i32* @q, align 4
>> > +// CHECK-DYN-NEXT: ret void
>> > +int q = p + f(); // m == 17 for this call; initialized to 56
>> > +
>> > +int y;
>> > +
>> > +// CHECK-STATIC-DAG: @b = global i32 2,
>> > +CONSTINIT int b = __builtin_is_constant_evaluated() ? 2 : y; // static initialization to 2
>> > +
>> > +// CHECK-DYN-LABEL: define internal void @__cxx_global_var_init.1()
>> > +// CHECK-DYN: %0 = load i32, i32* @y, align 4
>> > +// CHECK-DYN: %1 = load i32, i32* @y, align 4
>> > +// CHECK-DYN-NEXT: %add = add
>> > +// CHECK-DYN-NEXT: store i32 %add, i32* @c,
>> > +int c = y + (__builtin_is_constant_evaluated() ? 2 : y); // dynamic initialization to y+y
>> > +
>> > +// CHECK-DYN-LABEL: define internal void @__cxx_global_var_init.2()
>> > +// CHECK-DYN: store i32 1, i32* @_ZL1a, align 4
>> > +// CHECK-DYN-NEXT: ret void
>> > +const int a = __builtin_is_constant_evaluated() ? y : 1; // dynamic initialization to 1
>> > +const int *a_sink = &a;
>> > +
>> > +// CHECK-ARR-LABEL: define void @_Z13test_arr_exprv
>> > +void test_arr_expr() {
>> > + // CHECK-ARR: %x1 = alloca [101 x i8],
>> > + char x1[std::is_constant_evaluated() && __builtin_is_constant_evaluated() ? 101 : 1];
>> > +
>> > + // CHECK-ARR: %x2 = alloca [42 x i8],
>> > + char x2[std::is_constant_evaluated() && __builtin_is_constant_evaluated() ? 42 : RANDU()];
>> > +
>> > + // CHECK-ARR: call i8* @llvm.stacksave()
>> > + // CHECK-ARR: %vla = alloca i8, i64 13,
>> > + char x3[std::is_constant_evaluated() || __builtin_is_constant_evaluated() ? RANDU() : 13];
>> > +}
>> > +
>> > +// CHECK-ARR-LABEL: define void @_Z17test_new_arr_exprv
>> > +void test_new_arr_expr() {
>> > + // CHECK-ARR: call i8* @_Znam(i64 17)
>> > + new char[std::is_constant_evaluated() || __builtin_is_constant_evaluated() ? 1 : 17];
>> > +}
>> > +
>> > +// CHECK-FOLD-LABEL: @_Z31test_constant_initialized_locali(
>> > +bool test_constant_initialized_local(int k) {
>> > + // CHECK-FOLD: store i8 1, i8* %n,
>> > + // CHECK-FOLD: store volatile i8* %n, i8** %p,
>> > + const bool n = __builtin_is_constant_evaluated() && std::is_constant_evaluated();
>> > + const bool *volatile p = &n;
>> > + return *p;
>> > +}
>> > +
>> > +// CHECK-FOLD-LABEL: define void @_Z21test_ir_constant_foldv()
>> > +void test_ir_constant_fold() {
>> > + // CHECK-FOLD-NEXT: entry:
>> > + // CHECK-FOLD-NEXT: call void @OK()
>> > + // CHECK-FOLD-NEXT: call void @OK()
>> > + // CHECK-FOLD-NEXT: ret void
>> > + if (std::is_constant_evaluated()) {
>> > + BOOM();
>> > + } else {
>> > + OK();
>> > + }
>> > + std::is_constant_evaluated() ? BOOM() : OK();
>> > +}
>> > +
>> > +// CHECK-STATIC-DAG: @ir = constant i32* @i_constant,
>> > +int i_constant;
>> > +int i_not_constant;
>> > +int &ir = __builtin_is_constant_evaluated() ? i_constant : i_not_constant;
>> > +
>> > +// CHECK-FOLD-LABEL: @_Z35test_ref_initialization_local_scopev()
>> > +void test_ref_initialization_local_scope() {
>> > + const int i_constant = 42;
>> > + const int i_non_constant = 101;
>> > + // CHECK-FOLD: store i32* %i_non_constant, i32** %r,
>> > + const int &r = __builtin_is_constant_evaluated() ? i_constant : i_non_constant;
>> > +}
>> > +
>> > +// CHECK-FOLD-LABEL: @_Z22test_ref_to_static_varv()
>> > +void test_ref_to_static_var() {
>> > + static int i_constant = 42;
>> > + static int i_non_constant = 101;
>> > + // CHECK-FOLD: store i32* @_ZZ22test_ref_to_static_varvE10i_constant, i32** %r,
>> > + int &r = __builtin_is_constant_evaluated() ? i_constant : i_non_constant;
>> > +}
>> > \ No newline at end of file
>> >
>> > Modified: cfe/trunk/test/Sema/builtins.c
>> > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/builtins.c?rev=359067&r1=359066&r2=359067&view=diff
>> > ==============================================================================
>> > --- cfe/trunk/test/Sema/builtins.c (original)
>> > +++ cfe/trunk/test/Sema/builtins.c Tue Apr 23 19:23:30 2019
>> > @@ -314,3 +314,9 @@ void test23() {
>> > memcpy(buf, src, 11); // expected-warning{{'memcpy' will always overflow; destination buffer has size 10, but size argument is 11}}
>> > my_memcpy(buf, src, 11); // expected-warning{{'memcpy' will always overflow; destination buffer has size 10, but size argument is 11}}
>> > }
>> > +
>> > +// Test that __builtin_is_constant_evaluated() is not allowed in C
>> > +int test_cxx_builtin() {
>> > + // expected-error at +1 {{use of unknown builtin '__builtin_is_constant_evaluated'}}
>> > + return __builtin_is_constant_evaluated();
>> > +}
>> >
>> > Added: cfe/trunk/test/SemaCXX/builtin-is-constant-evaluated.cpp
>> > URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/SemaCXX/builtin-is-constant-evaluated.cpp?rev=359067&view=auto
>> > ==============================================================================
>> > --- cfe/trunk/test/SemaCXX/builtin-is-constant-evaluated.cpp (added)
>> > +++ cfe/trunk/test/SemaCXX/builtin-is-constant-evaluated.cpp Tue Apr 23 19:23:30 2019
>> > @@ -0,0 +1,121 @@
>> > +// RUN: %clang_cc1 -std=c++2a -verify %s -fcxx-exceptions -triple=x86_64-linux-gnu
>> > +
>> > +using size_t = decltype(sizeof(int));
>> > +
>> > +namespace std {
>> > +inline constexpr bool is_constant_evaluated() noexcept {
>> > + return __builtin_is_constant_evaluated();
>> > +}
>> > +} // namespace std
>> > +
>> > +extern int dummy; // expected-note 1+ {{declared here}}
>> > +
>> > +static_assert(__builtin_is_constant_evaluated());
>> > +static_assert(noexcept(__builtin_is_constant_evaluated()));
>> > +
>> > +constexpr bool b = __builtin_is_constant_evaluated();
>> > +static_assert(b);
>> > +
>> > +const int n = __builtin_is_constant_evaluated() ? 4 : dummy;
>> > +static_assert(n == 4);
>> > +constexpr int cn = __builtin_is_constant_evaluated() ? 11 : dummy;
>> > +static_assert(cn == 11);
>> > +// expected-error at +1 {{'bn' must be initialized by a constant expression}}
>> > +constexpr int bn = __builtin_is_constant_evaluated() ? dummy : 42; // expected-note {{non-const variable 'dummy' is not allowed}}
>> > +
>> > +const int n2 = __builtin_is_constant_evaluated() ? dummy : 42; // expected-note {{declared here}}
>> > +static_assert(n2 == 42); // expected-error {{static_assert expression is not an integral constant}}
>> > +// expected-note at -1 {{initializer of 'n2' is not a constant expression}}
>> > +
>> > +template <bool V, bool Default = std::is_constant_evaluated()>
>> > +struct Templ { static_assert(V); static_assert(Default); };
>> > +Templ<__builtin_is_constant_evaluated()> x; // type X<true>
>> > +
>> > +template <class T>
>> > +void test_if_constexpr() {
>> > + if constexpr (__builtin_is_constant_evaluated()) {
>> > + static_assert(__is_same(T, int));
>> > + } else {
>> > + using Test = typename T::DOES_NOT_EXIST;
>> > + }
>> > +}
>> > +template void test_if_constexpr<int>();
>> > +
>> > +void test_array_decl() {
>> > + char x[__builtin_is_constant_evaluated() + std::is_constant_evaluated()];
>> > + static_assert(sizeof(x) == 2, "");
>> > +}
>> > +
>> > +void test_case_stmt(int x) {
>> > + switch (x) {
>> > + case 0: // OK
>> > + case __builtin_is_constant_evaluated(): // expected-note {{previous case}}
>> > + case std::is_constant_evaluated() + __builtin_is_constant_evaluated(): // expected-note {{previous case}}
>> > + case 1: // expected-error {{duplicate case value '1'}}
>> > + case 2: // expected-error {{duplicate case value '2'}}
>> > + break;
>> > + }
>> > +}
>> > +
>> > +constexpr size_t good_array_size() {
>> > + return std::is_constant_evaluated() ? 42 : static_cast<size_t>(-1);
>> > +}
>> > +
>> > +constexpr size_t bad_array_size() {
>> > + return std::is_constant_evaluated() ? static_cast<size_t>(-1) : 13;
>> > +}
>> > +
>> > +template <class T>
>> > +constexpr T require_constexpr(T v) {
>> > + if (!std::is_constant_evaluated())
>> > + throw "BOOM";
>> > + return v;
>> > +}
>> > +
>> > +void test_new_expr() {
>> > + constexpr size_t TooLarge = -1;
>> > + auto *x = new int[std::is_constant_evaluated() ? 1 : TooLarge]; // expected-error {{array is too large}}
>> > + auto *x2 = new int[std::is_constant_evaluated() ? TooLarge : 1]; // OK
>> > + auto *y = new int[1][std::is_constant_evaluated() ? TooLarge : 1]{}; // expected-error {{array is too large}}
>> > + auto *y2 = new int[1][require_constexpr(42)];
>> > +}
>> > +
>> > +void test_alignas_operand() {
>> > + alignas(std::is_constant_evaluated() ? 8 : 2) char dummy;
>> > + static_assert(__alignof(dummy) == 8);
>> > +}
>> > +
>> > +void test_static_assert_operand() {
>> > + static_assert(std::is_constant_evaluated(), "");
>> > +}
>> > +
>> > +void test_enumerator() {
>> > + enum MyEnum {
>> > + ZERO = 0,
>> > + ONE = std::is_constant_evaluated()
>> > + };
>> > + static_assert(ONE == 1, "");
>> > +}
>> > +
>> > +struct TestBitfieldWidth {
>> > + unsigned Bits : std::is_constant_evaluated();
>> > +};
>> > +
>> > +void test_operand_of_noexcept_fn() noexcept(std::is_constant_evaluated());
>> > +static_assert(noexcept(test_operand_of_noexcept_fn()), "");
>> > +
>> > +
>> > +namespace test_ref_initialization {
>> > +int x;
>> > +int y;
>> > +int &r = __builtin_is_constant_evaluated() ? x : y;
>> > +static_assert(&r == &x);
>> > +
>> > +} // namespace test_ref_initialization
>> > +
>> > +#if defined(__cpp_conditional_explicit)
>> > +struct TestConditionalExplicit {
>> > + explicit(__builtin_is_constant_evaluated()) TestConditionalExplicit(int) {}
>> > +};
>> > +TestConditionalExplicit e = 42;
>> > +#endif
>> >
>> >
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