r291416 - [cxx1z-constexpr-lambda] Implement constant evaluation of non-capturing lambda expressions.
Richard Smith via cfe-commits
cfe-commits at lists.llvm.org
Sun Jan 8 22:13:18 PST 2017
On 8 January 2017 at 19:02, Faisal Vali via cfe-commits <
cfe-commits at lists.llvm.org> wrote:
> Author: faisalv
> Date: Sun Jan 8 21:02:53 2017
> New Revision: 291416
>
> URL: http://llvm.org/viewvc/llvm-project?rev=291416&view=rev
> Log:
> [cxx1z-constexpr-lambda] Implement constant evaluation of non-capturing
> lambda expressions.
>
> Add a visitor for lambda expressions to RecordExprEvaluator in
> ExprConstant.cpp that creates an empty APValue of Struct type to represent
> the closure object. Additionally, add a LambdaExpr visitor to the
> TemporaryExprEvaluator that forwards constant evaluation of
> immediately-called-lambda-expressions to the one in RecordExprEvaluator
> through VisitConstructExpr.
>
> This patch supports:
> constexpr auto ID = [] (auto a) { return a; };
> static_assert(ID(3.14) == 3.14);
> static_assert([](auto a) { return a + 1; }(10) == 11);
>
> Lambda captures are still not supported for constexpr lambdas.
>
>
> Modified:
> cfe/trunk/lib/AST/ExprConstant.cpp
> cfe/trunk/lib/Sema/SemaExpr.cpp
> cfe/trunk/test/SemaCXX/cxx1z-constexpr-lambdas.cpp
>
> Modified: cfe/trunk/lib/AST/ExprConstant.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/
> ExprConstant.cpp?rev=291416&r1=291415&r2=291416&view=diff
> ============================================================
> ==================
> --- cfe/trunk/lib/AST/ExprConstant.cpp (original)
> +++ cfe/trunk/lib/AST/ExprConstant.cpp Sun Jan 8 21:02:53 2017
> @@ -5868,6 +5868,7 @@ namespace {
> bool VisitCXXConstructExpr(const CXXConstructExpr *E) {
> return VisitCXXConstructExpr(E, E->getType());
> }
> + bool VisitLambdaExpr(const LambdaExpr *E);
> bool VisitCXXInheritedCtorInitExpr(const CXXInheritedCtorInitExpr
> *E);
> bool VisitCXXConstructExpr(const CXXConstructExpr *E, QualType T);
> bool VisitCXXStdInitializerListExpr(const CXXStdInitializerListExpr
> *E);
> @@ -6202,6 +6203,21 @@ bool RecordExprEvaluator::VisitCXXStdIni
> return true;
> }
>
> +bool RecordExprEvaluator::VisitLambdaExpr(const LambdaExpr *E) {
> + const CXXRecordDecl *ClosureClass = E->getLambdaClass();
> + if (ClosureClass->isInvalidDecl()) return false;
> +
> + if (Info.checkingPotentialConstantExpression()) return true;
> + if (E->capture_size()) {
> + Info.FFDiag(E, diag::note_unimplemented_constexpr_lambda_feature_ast)
> + << "can not evaluate lambda expressions with captures";
> + return false;
> + }
> + // FIXME: Implement captures.
> + Result = APValue(APValue::UninitStruct(), /*NumBases*/0,
> /*NumFields*/0);
> + return true;
> +}
> +
> static bool EvaluateRecord(const Expr *E, const LValue &This,
> APValue &Result, EvalInfo &Info) {
> assert(E->isRValue() && E->getType()->isRecordType() &&
> @@ -6251,6 +6267,9 @@ public:
> bool VisitCXXStdInitializerListExpr(const CXXStdInitializerListExpr
> *E) {
> return VisitConstructExpr(E);
> }
> + bool VisitLambdaExpr(const LambdaExpr *E) {
> + return VisitConstructExpr(E);
> + }
> };
> } // end anonymous namespace
>
>
> Modified: cfe/trunk/lib/Sema/SemaExpr.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/
> SemaExpr.cpp?rev=291416&r1=291415&r2=291416&view=diff
> ============================================================
> ==================
> --- cfe/trunk/lib/Sema/SemaExpr.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaExpr.cpp Sun Jan 8 21:02:53 2017
> @@ -13097,8 +13097,10 @@ void Sema::PopExpressionEvaluationContex
> // evaluate [...] a lambda-expression.
> D = diag::err_lambda_in_constant_expression;
> }
> - for (const auto *L : Rec.Lambdas)
> - Diag(L->getLocStart(), D);
> + // C++1z allows lambda expressions as core constant expressions.
> + if (Rec.Context != ConstantEvaluated || !getLangOpts().CPlusPlus1z)
> + for (const auto *L : Rec.Lambdas)
> + Diag(L->getLocStart(), D);
>
We'll need an implementation of DR1607 before we're done here, since it
looks like this has removed the last restriction on lambda-expressions in
function template signatures in some contexts (array bounds, template
arguments).
} else {
> // Mark the capture expressions odr-used. This was deferred
> // during lambda expression creation.
>
> Modified: cfe/trunk/test/SemaCXX/cxx1z-constexpr-lambdas.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/
> SemaCXX/cxx1z-constexpr-lambdas.cpp?rev=291416&r1=
> 291415&r2=291416&view=diff
> ============================================================
> ==================
> --- cfe/trunk/test/SemaCXX/cxx1z-constexpr-lambdas.cpp (original)
> +++ cfe/trunk/test/SemaCXX/cxx1z-constexpr-lambdas.cpp Sun Jan 8
> 21:02:53 2017
> @@ -96,4 +96,81 @@ decltype(deduced_return_type(0)) d; //e
>
> } // end ns test_conversion_function_for_non_capturing_lambdas
>
> +namespace test_lambda_is_cce {
> +namespace ns1_simple_lambda {
> +
> +namespace ns0 {
> +constexpr int I = [](auto a) { return a; }(10);
> +
> +static_assert(I == 10);
> +static_assert(10 == [](auto a) { return a; }(10));
> +static_assert(3.14 == [](auto a) { return a; }(3.14));
> +
> +} //end ns0
> +
> +namespace ns1 {
> +constexpr auto f(int i) {
> + double d = 3.14;
> + auto L = [=](auto a) {
> + int Isz = sizeof(i);
> + return sizeof(i) + sizeof(a) + sizeof(d);
> + };
> + int I = L("abc") + L(nullptr);
> + return L;
> +}
> +constexpr auto L = f(3);
> +constexpr auto M = L("abc") + L(nullptr);
> +
> +static_assert(M == sizeof(int) * 2 + sizeof(double) * 2 + sizeof(nullptr)
> + sizeof(const char*));
> +
> +} // end ns1
> +
> +namespace ns2 {
> +constexpr auto f(int i) {
> + auto L = [](auto a) { return a + a; };
> + return L;
> +}
> +constexpr auto L = f(3);
> +constexpr int I = L(6);
> +static_assert(I == 12);
> +} // end ns2
> +
> +namespace contained_lambdas_call_operator_is_not_constexpr {
> +constexpr auto f(int i) {
> + double d = 3.14;
> + auto L = [=](auto a) { //expected-note{{declared here}}
> + int Isz = sizeof(i);
> + asm("hello");
> + return sizeof(i) + sizeof(a) + sizeof(d);
> + };
> + return L;
> +}
> +
> +constexpr auto L = f(3);
> +
> +constexpr auto M = // expected-error{{must be initialized by}}
> + L("abc"); //expected-note{{non-constexpr function}}
> +
> +} // end ns contained_lambdas_call_operator_is_not_constexpr
> +
> +
> +
> +} // end ns1_simple_lambda
> +
> +namespace ns1_unimplemented {
> +namespace ns1_captures {
> +constexpr auto f(int i) {
> + double d = 3.14;
> + auto L = [=](auto a) { //expected-note{{coming soon}}
> + int Isz = i + d;
> + return sizeof(i) + sizeof(a) + sizeof(d);
> + };
> + return L;
> +}
> +constexpr auto M = f(3); //expected-error{{constant expression}}
> expected-note{{in call to}}
> +} // end ns1_captures
> +} // end ns1_unimplemented
> +
> +} // end ns test_lambda_is_cce
> +
> #endif // ndef CPP14_AND_EARLIER
>
>
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