Summary:
The messages for two of the warnings are misleading:
* warn_for_range_const_reference_copy suggests that the initialization
of the loop variable results in a copy. But that's not always true,
we just know that some conversion happens, potentially invoking a
constructor or conversion operator. The constructor might copy, as in
the example that lead to this message [1], but it might also not.
However, the constructed object is bound to a reference, which is
potentially misleading, so we rewrite the message to emphasize that.
We also make sure that we print the reference type into the warning
message to clarify that this warning only appears when operator*
returns a reference.
* warn_for_range_variable_always_copy suggests that a reference type
loop variable initialized from a temporary "is always a copy". But
we don't know this, the range might just return temporary objects
which aren't copies of anything. (Assuming RVO a copy constructor
might never have been called.)
The message for warn_for_range_copy is a bit repetitive: the type of a
VarDecl and its initialization Expr are the same up to cv-qualifiers,
because Sema will insert implicit casts or constructor calls to make
them match.
[1] https://bugs.llvm.org/show_bug.cgi?id=32823
Reviewers: aaron.ballman, Mordante, rtrieu
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D75613
During the review of D73007 Aaron Puchert mentioned
`warn_for_range_variable_always_copy` shouldn't be part of -Wall since
some coding styles require `for(const auto &bar : bars)`. This warning
would cause false positives for these users. Based on Aaron's proposal
refactored the warnings:
* -Wrange-loop-construct warns about possibly unintended constructor
calls. This is part of -Wall. It contains
* warn_for_range_copy: loop variable A of type B creates a copy from
type C
* warn_for_range_const_reference_copy: loop variable A is initialized
with a value of a different type resulting in a copy
* -Wrange-loop-bind-reference warns about misleading use of reference
types. This is not part of -Wall. It contains
* warn_for_range_variable_always_copy: loop variable A is always a copy
because the range of type B does not return a reference
Differential Revision: https://reviews.llvm.org/D73434
When Wrange-loop-analysis issues a diagnostic on a dependent type in a
template the diagnostic may not be valid for all instantiations. Therefore
the diagnostic is suppressed during the instantiation. Non dependent types
still issue a diagnostic.
The same can happen when using macros. Therefore the diagnostic is
disabled for macros.
Fixes https://bugs.llvm.org/show_bug.cgi?id=44556
Differential Revision: https://reviews.llvm.org/D73007
No longer generate a diagnostic when a small trivially copyable type is
used without a reference. Before the test looked for a POD type and had no
size restriction. Since the range-based for loop is only available in
C++11 and POD types are trivially copyable in C++11 it's not required to
test for a POD type.
Since copying a large object will be expensive its size has been
restricted. 64 bytes is a common size of a cache line and if the object is
aligned the copy will be cheap. No performance impact testing has been
done.
Differential Revision: https://reviews.llvm.org/D72212
This makes the range loop warnings part of -Wall.
Fixes PR32823: Warn about accidental coping of data in range based for
Differential Revision: https://reviews.llvm.org/D68912
Recomitted after fixing the warnings it created.
This makes the range loop warnings part of -Wall.
Fixes PR32823: Warn about accidental coping of data in range based for
Differential Revision: https://reviews.llvm.org/D68912
The Wrange-loop-analyses warns if a copy is made. Suppress this warning when
a temporary is bound to a rvalue reference.
While fixing this issue also found a copy-paste error in test6, which is also
fixed.
Differential Revision: https://reviews.llvm.org/D71806
-Wrange-loop-analysis is a subgroup of -Wloop-analysis and will warn when
a range-based for-loop makes copies of the elements in the range. If possible,
suggest the proper type to prevent copies, or the non-reference to help
distinguish copy versus non-copy forms. Existing warnings in -Wloop-analysis
are moved to -Wfor-loop-analysis, also a subgroup of -Wloop-analysis.
Differential Revision: http://reviews.llvm.org/D4169
llvm-svn: 234804
Aaron Puchert