On Mon, Jan 9, 2017 at 12:13 AM, Richard Smith <rich...@metafoo.co.uk> wrote:
> On 8 January 2017 at 19:02, Faisal Vali via cfe-commits
> <cfe-commits@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).
>
Yes - I'll add those restrictions back (I suppose we'll need to check
whether the nearest enclosing non-lambda context is a valid one [while
still allowing them in default function arguments]) - but then we'll
need to relax some of them when we implement P0315 in post-C++-17
right?
For e.g. these would be ok w P0315 right?
template<int N = []{ return 5; }()> struct X { };
X<[](auto a){ return a; }(10)> x;
Thanks!
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
