(This relands 59337263ab and makes sure comma operator
diagnostics are suppressed in a SFINAE context.)
While at it, add the diagnosis message "left operand of comma operator has no effect" (used by GCC) for comma operator.
This also makes Clang diagnose in the constant evaluation context which aligns with GCC/MSVC behavior. (https://godbolt.org/z/7zxb8Tx96)
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D103938
While at it, add the diagnosis message "left operand of comma operator has no effect" (used by GCC) for comma operator.
This also makes Clang diagnose in the constant evaluation context which aligns with GCC/MSVC behavior. (https://godbolt.org/z/7zxb8Tx96)
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D103938
See PR51862.
The consumers of the Elidable flag in CXXConstructExpr assume that
an elidable construction just goes through a single copy/move construction,
so that the source object is immediately passed as an argument and is the same
type as the parameter itself.
With the implementation of P2266 and after some adjustments to the
implementation of P1825, we started (correctly, as per standard)
allowing more cases where the copy initialization goes through
user defined conversions.
With this patch we stop using this flag in NRVO contexts, to preserve code
that relies on that assumption.
This causes no known functional changes, we just stop firing some asserts
in a cople of included test cases.
Reviewed By: rsmith
Differential Revision: https://reviews.llvm.org/D109800
While at it, add the diagnosis message "left operand of comma operator has no effect" (used by GCC) for comma operator.
This also makes Clang diagnose in the constant evaluation context which aligns with GCC/MSVC behavior. (https://godbolt.org/z/7zxb8Tx96)
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D103938
See PR51842.
This fixes an assert firing in the static analyzer, triggered by implicit moves
in blocks in C mode:
This also simplifies the AST a little bit when compiling non C++ code,
as the xvalue implicit casts are not inserted.
We keep and test that the nrvo flag is still being set on the VarDecls,
as that is still a bit beneficial while not really making anything
more complicated.
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: NoQ
Differential Revision: https://reviews.llvm.org/D109654
This patch replaces the workaround for simpler implicit moves
implemented in D105518.
The Microsoft STL currently has some issues with P2266.
Where before, with -fms-compatibility, we would disable simpler
implicit moves globally, with this change, we disable it only
when the returned expression is in a context contained by
std namespace and is located within a system header.
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: aaron.ballman, mibintc
Differential Revision: https://reviews.llvm.org/D105951
An empty enum is used to implement C++'s new-ish "byte" type (to make
sure it's a separate type for overloading, etc - compared to a typedef)
- without any enumerators. Some clang warnings don't make sense in this
sort of situation, so let's skip them for empty enums.
It's arguable that possibly some situations of enumerations without
enumerators might want the previous-to-this-patch behavior (if the enum
is autogenerated and in some cases comes up empty, then maybe a default
in an empty switch would still be considered problematic - so that when
you add the first enumeration you do get a -Wswitch warning). But I
think that's niche enough & this std::byte case is mainstream enough
that we should prioritize the latter over the former.
If someone's got a middle ground proposal to account for both of those
situations, I'm open to patches/suggestions/etc.
When disabling simpler implicit moves in MSVC compatibility mode as
a workaround in D105518, we forgot to make the opposite change and
enable regular (P1825) implicit moves in the same mode.
As a result, we were not doing any implicit moves at all. OOPS!
This fixes it and adds test for this.
This is a fix to a temporary workaround, there is ongoing
work to replace this, applying the workaround only to
system headers and the ::stl namespace.
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D106303
After taking C++98 implicit moves out in D104500,
we put it back in, but now in a new form which preserves
compatibility with pure C++98 programs, while at the same time
giving almost all the goodies from P1825.
* We use the exact same rules as C++20 with regards to which
id-expressions are move eligible. The previous
incarnation would only benefit from the proper subset which is
copy ellidable. This means we can implicit move, in addition:
* Parameters.
* RValue references.
* Exception variables.
* Variables with higher-than-natural required alignment.
* Objects with different type from the function return type.
* We preserve the two-overload resolution, with one small tweak to the
first one: If we either pick a (possibly converting) constructor which
does not take an rvalue reference, or a user conversion operator which
is not ref-qualified, we abort into the second overload resolution.
This gives C++98 almost all the implicit move patterns which we had created test
cases for, while at the same time preserving the meaning of these
three patterns, which are found in pure C++98 programs:
* Classes with both const and non-const copy constructors, but no move
constructors, continue to have their non-const copy constructor
selected.
* We continue to reject as ambiguous the following pattern:
```
struct A { A(B &); };
struct B { operator A(); };
A foo(B x) { return x; }
```
* We continue to pick the copy constructor in the following pattern:
```
class AutoPtrRef { };
struct AutoPtr {
AutoPtr(AutoPtr &);
AutoPtr();
AutoPtr(AutoPtrRef);
operator AutoPtrRef();
};
AutoPtr test_auto_ptr() {
AutoPtr p;
return p;
}
```
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: Quuxplusone
Differential Revision: https://reviews.llvm.org/D105756
C++23 will make these conversions ambiguous - so fix them to make the
codebase forward-compatible with C++23 (& a follow-up change I've made
will make this ambiguous/invalid even in <C++23 so we don't regress
this & it generally improves the code anyway)
The Microsoft STL currently has some issues with P2266.
We disable it for now in that mode, but we might come back later with a
more targetted approach.
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D105518
Named return of a variable with aligned attribute would
trip an assert in case alignment was dependent.
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: rsmith
Differential Revision: https://reviews.llvm.org/D105380
Named return of a variable with aligned attribute would
trip an assert in case alignment was dependent.
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: rsmith
Differential Revision: https://reviews.llvm.org/D105380
This extends the effects of [[ http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1825r0.html | P1825 ]] to all C++ standards from C++11 up to C++20.
According to Motion 23 from Cologne 2019, P1825R0 was accepted as a Defect Report, so we retroactively apply this all the way back to C++11.
Note that we also remove implicit moves from C++98 as an extension
altogether, since the expanded first overload resolution from P1825
can cause some meaning changes in C++98.
For example it can change which copy constructor is picked when both const
and non-const ones are available.
This also rips out warn_return_std_move since there are no cases where it would be worthwhile to suggest it.
This also fixes a bug with bailing into the second overload resolution
when encountering a non-rvref qualified conversion operator.
This was unnoticed until now, so two new test cases cover these.
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: rsmith
Differential Revision: https://reviews.llvm.org/D104500
This expands NRVO propagation for more cases:
Parse analysis improvement:
* Lambdas and Blocks with dependent return type can have their variables
marked as NRVO Candidates.
Variable instantiation improvements:
* Fixes crash when instantiating NRVO variables in Blocks.
* Functions, Lambdas, and Blocks which have auto return type have their
variables' NRVO status propagated. For Blocks with non-auto return type,
as a limitation, this propagation does not consider the actual return
type.
This also implements exclusion of VarDecls which are references to
dependent types.
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: Quuxplusone
Differential Revision: https://reviews.llvm.org/D99696
This change caused build errors related to move-only __block variables,
see discussion on https://reviews.llvm.org/D99696
> This expands NRVO propagation for more cases:
>
> Parse analysis improvement:
> * Lambdas and Blocks with dependent return type can have their variables
> marked as NRVO Candidates.
>
> Variable instantiation improvements:
> * Fixes crash when instantiating NRVO variables in Blocks.
> * Functions, Lambdas, and Blocks which have auto return type have their
> variables' NRVO status propagated. For Blocks with non-auto return type,
> as a limitation, this propagation does not consider the actual return
> type.
>
> This also implements exclusion of VarDecls which are references to
> dependent types.
>
> Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
>
> Reviewed By: Quuxplusone
>
> Differential Revision: https://reviews.llvm.org/D99696
This also reverts the follow-on change which was hard to tease apart
form the one above:
> "[clang] Implement P2266 Simpler implicit move"
>
> This Implements [[http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2266r1.html|P2266 Simpler implicit move]].
>
> Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
>
> Reviewed By: Quuxplusone
>
> Differential Revision: https://reviews.llvm.org/D99005
This reverts commits 1e50c3d785 and
bf20631782.
This expands NRVO propagation for more cases:
Parse analysis improvement:
* Lambdas and Blocks with dependent return type can have their variables
marked as NRVO Candidates.
Variable instantiation improvements:
* Fixes crash when instantiating NRVO variables in Blocks.
* Functions, Lambdas, and Blocks which have auto return type have their
variables' NRVO status propagated. For Blocks with non-auto return type,
as a limitation, this propagation does not consider the actual return
type.
This also implements exclusion of VarDecls which are references to
dependent types.
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: Quuxplusone
Differential Revision: https://reviews.llvm.org/D99696
<string> is currently the highest impact header in a clang+llvm build:
https://commondatastorage.googleapis.com/chromium-browser-clang/llvm-include-analysis.html
One of the most common places this is being included is the APInt.h header, which needs it for an old toString() implementation that returns std::string - an inefficient method compared to the SmallString versions that it actually wraps.
This patch replaces these APInt/APSInt methods with a pair of llvm::toString() helpers inside StringExtras.h, adjusts users accordingly and removes the <string> from APInt.h - I was hoping that more of these users could be converted to use the SmallString methods, but it appears that most end up creating a std::string anyhow. I avoided trying to use the raw_ostream << operators as well as I didn't want to lose having the integer radix explicit in the code.
Differential Revision: https://reviews.llvm.org/D103888
This expands NRVO propagation for more cases:
Parse analysis improvement:
* Lambdas and Blocks with dependent return type can have their variables
marked as NRVO Candidates.
Variable instantiation improvements:
* Fixes crash when instantiating NRVO variables in Blocks.
* Functions, Lambdas, and Blocks which have auto return type have their
variables' NRVO status propagated. For Blocks with non-auto return type,
as a limitation, this propagation does not consider the actual return
type.
This also implements exclusion of VarDecls which are references to
dependent types.
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: Quuxplusone
Differential Revision: https://reviews.llvm.org/D99696
This renames the expression value categories from rvalue to prvalue,
keeping nomenclature consistent with C++11 onwards.
C++ has the most complicated taxonomy here, and every other language
only uses a subset of it, so it's less confusing to use the C++ names
consistently, and mentally remap to the C names when working on that
context (prvalue -> rvalue, no xvalues, etc).
Renames:
* VK_RValue -> VK_PRValue
* Expr::isRValue -> Expr::isPRValue
* SK_QualificationConversionRValue -> SK_QualificationConversionPRValue
* JSON AST Dumper Expression nodes value category: "rvalue" -> "prvalue"
Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>
Reviewed By: rsmith
Differential Revision: https://reviews.llvm.org/D103720
Warn when a declaration uses an identifier that doesn't obey the reserved
identifier rule from C and/or C++.
Differential Revision: https://reviews.llvm.org/D93095
These are intended to mimic warnings available in gcc.
-Wunused-but-set-variable is triggered in the case of a variable which
appears on the LHS of an assignment but not otherwise used.
For instance:
void f() {
int x;
x = 0;
}
-Wunused-but-set-parameter works similarly, but for function parameters
instead of variables.
In C++, they are triggered only for scalar types; otherwise, they are
triggered for all types. This is gcc's behavior.
-Wunused-but-set-parameter is controlled by -Wextra, while
-Wunused-but-set-variable is controlled by -Wunused. This is slightly
different from gcc's behavior, but seems most consistent with clang's
behavior for -Wunused-parameter and -Wunused-variable.
Reviewed By: aeubanks
Differential Revision: https://reviews.llvm.org/D100581
This is a Clang-only change and depends on the existing "musttail"
support already implemented in LLVM.
The [[clang::musttail]] attribute goes on a return statement, not
a function definition. There are several constraints that the user
must follow when using [[clang::musttail]], and these constraints
are verified by Sema.
Tail calls are supported on regular function calls, calls through a
function pointer, member function calls, and even pointer to member.
Future work would be to throw a warning if a users tries to pass
a pointer or reference to a local variable through a musttail call.
Reviewed By: rsmith
Differential Revision: https://reviews.llvm.org/D99517
This changes our approach to processing statement attributes to be more
similar to how we process declaration attributes. Namely,
ActOnAttributedStmt() now calls ProcessStmtAttributes() instead of
vice-versa, and there is now an interface split between building an
attributed statement where you already have a list of semantic
attributes and building an attributed statement with attributes from
the parser.
This should make it easier to support statement attributes that are
dependent on a template. In that case, you would add a
TransformFooAttr() function in TreeTransform.h to perform the semantic
checking (morally similar to how Sema::InstantiateAttrs() already works
for declaration attributes) when transforming the semantic attribute at
instantiation time.
Review D88220 turns out to have some pretty severe bugs, but I *think*
this patch fixes them.
Paper P1825 is supposed to enable implicit move from "non-volatile objects
and rvalue references to non-volatile object types." Instead, what was committed
seems to have enabled implicit move from "non-volatile things of all kinds,
except that if they're rvalue references then they must also refer to non-volatile
things." In other words, D88220 accidentally enabled implicit move from
lvalue object references (super yikes!) and also from non-object references
(such as references to functions).
These two cases are now fixed and regression-tested.
Differential Revision: https://reviews.llvm.org/D98971
The condition variable is in scope in the loop increment, so we need to
emit the jump destination from wthin the scope of the condition
variable.
For GCC compatibility (and compatibility with real-world 'FOR_EACH'
macros), 'continue' is permitted in a statement expression within the
condition of a for loop, though, so there are two cases here:
* If the for loop has no condition variable, we can emit the jump
destination before emitting the condition.
* If the for loop has a condition variable, we must defer emitting the
jump destination until after emitting the variable. We diagnose a
'continue' appearing in the initializer of the condition variable,
because it would jump past the initializer into the scope of that
variable.
Reviewed By: rjmccall
Differential Revision: https://reviews.llvm.org/D98816
Implement all of P1825R0:
- implicitly movable entity can be an rvalue reference to non-volatile
automatic object.
- operand of throw-expression can be a function or catch-clause parameter
(support for function parameter has already been implemented).
- in the first overload resolution, the selected function no need to be
a constructor.
- in the first overload resolution, the first parameter of the selected
function no need to be an rvalue reference to the object's type.
This patch also removes the diagnostic `-Wreturn-std-move-in-c++11`.
Differential Revision: https://reviews.llvm.org/D88220
The ordered comparison operators are defined for the SourceLocation
class, so SourceLocation objects can be compared directly. There is no
need to extract the internal representation for comparison.
Reviewed By: aprantl
Differential Revision: https://reviews.llvm.org/D94231
In implicitly movable test, a two-stage overload resolution is performed.
If the first overload resolution selects a deleted function, Clang directly
performs the second overload resolution, without checking whether the
deleted function matches the additional criteria.
This patch fixes the above problem.
Reviewed By: Quuxplusone
Differential Revision: https://reviews.llvm.org/D92936
In implicitly movable test, a two-stage overload resolution is performed.
If the first overload resolution selects a deleted function, Clang directly
performs the second overload resolution, without checking whether the
deleted function matches the additional criteria.
This patch fixes the above problem.
Reviewed By: Quuxplusone
Differential Revision: https://reviews.llvm.org/D92936
We currently reject this valid C construct by claiming it declares a
non-local variable: for (struct { int i; } s={0}; s.i != 0; s.i--) ;
We expected all declaration in the clause-1 declaration statement to be
a local VarDecl, but there can be other declarations involved such as a
tag declaration. This fixes PR35757.
Given the following case:
```
auto k() {
return undef();
return 1;
}
```
Prior to the patch, clang emits an `cannot initialize return object of type
'auto' with an rvalue of type 'int'` diagnostic on the second return
(because the return type of the function cannot be deduced from the first contain-errors return).
This patch suppresses this error.
Differential Revision: https://reviews.llvm.org/D92211
In C++11 standard, to become implicitly movable, the expression in return
statement should be a non-volatile automatic object. CWG1579 changed the rule
to require that the expression only needs to be an automatic object. C++14
standard and C++17 standard kept this rule unchanged. C++20 standard changed
the rule back to require the expression be a non-volatile automatic object.
This should be a typo in standards, and VD should be non-volatile.
Differential Revision: https://reviews.llvm.org/D88295
Adds a diagnostic when the user annotates an `if constexpr` with a
likelihood attribute. The `if constexpr` statement is evaluated at compile
time so the attribute has no effect. Annotating the accompanied `else`
with a likelihood attribute has the same effect as annotating a generic
statement. Since the attribute there is most likely not intended, a
diagnostic will be issued. Since the attributes can't conflict, the
"conflict" won't be diagnosed for an `if constexpr`.
Differential Revision: https://reviews.llvm.org/D90336
Yuanfang Chen