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author | Marek Polacek <polacek@redhat.com> | 2022-10-18 12:20:14 -0400 |
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committer | Marek Polacek <polacek@redhat.com> | 2022-10-19 15:27:56 -0400 |
commit | b3c98d6a59a6dcd5b0b52bd5676b586ef4fe785f (patch) | |
tree | 8f9a87dcd0a886370934e88cff686d89d84c7d23 /gcc/doc | |
parent | 79d38dd46e6b07e5a90ab25df1438eb0918eb475 (diff) | |
download | gcc-b3c98d6a59a6dcd5b0b52bd5676b586ef4fe785f.zip gcc-b3c98d6a59a6dcd5b0b52bd5676b586ef4fe785f.tar.gz gcc-b3c98d6a59a6dcd5b0b52bd5676b586ef4fe785f.tar.bz2 |
c++: Mitigate -Wuseless-cast with classes [PR85043]
-Wuseless-cast (not part of -Wall/-Wextra) warns here:
struct S { };
void g (S&&);
void f (S&& arg)
{
g (S(arg)); // warning: useless cast to type 'struct S'
}
which is wrong: the code will not compile without the cast because
"arg" is an lvalue which cannot bind to S&&.
This patch disables the warning when an object that isn't a prvalue
is cast to a non-reference type. Therefore we still warn about the
useless cast in "X(X{})".
PR c++/85043
gcc/cp/ChangeLog:
* typeck.cc (maybe_warn_about_useless_cast): Don't warn when
a glvalue is cast to a non-reference type.
gcc/ChangeLog:
* doc/invoke.texi: Update documentation of -Wuseless-cast.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wuseless-cast.C: Remove dg-warning.
* g++.dg/warn/Wuseless-cast3.C: New test.
Diffstat (limited to 'gcc/doc')
-rw-r--r-- | gcc/doc/invoke.texi | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index c176e2d..cd4d3c1 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -4551,7 +4551,18 @@ pointers after reallocation. @item -Wuseless-cast @r{(C++ and Objective-C++ only)} @opindex Wuseless-cast @opindex Wno-useless-cast -Warn when an expression is casted to its own type. +Warn when an expression is cast to its own type. This warning does not +occur when a class object is converted to a non-reference type as that +is a way to create a temporary: + +@smallexample +struct S @{ @}; +void g (S&&); +void f (S&& arg) +@{ + g (S(arg)); // make arg prvalue so that it can bind to S&& +@} +@end smallexample @item -Wno-conversion-null @r{(C++ and Objective-C++ only)} @opindex Wconversion-null |