[Bug c++/98429] New: Some FMA expressions are evaluated less efficiently when -ffast-math is active
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98429 Bug ID: 98429 Summary: Some FMA expressions are evaluated less efficiently when -ffast-math is active Product: gcc Version: 10.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: chtz at informatik dot uni-bremen.de Target Milestone: --- If you compile an expression like x - x*y using fast-math optimizations it appears to get re-arranged to x*(1-y) which is (probably) never more efficient than the original expression, especially if the target supports FMA operations. Simple godbolt demonstration: https://godbolt.org/z/4q1oj9 (This is very likely not C++ specific, but I'm not sure what the correct component is -- I also just tried this for AVX-FMA)
[Bug c++/89325] [7/8/9/10 Regression] False warnings about "optimization attribute" on operators when -fno-ipa-cp-clone
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89325 Christoph Hertzberg changed: What|Removed |Added CC||chtz at informatik dot uni-bremen. ||de --- Comment #6 from Christoph Hertzberg --- Related: http://eigen.tuxfamily.org/bz/show_bug.cgi?id=1724 We just mask the warning for g++-7 at the moment.
[Bug c++/84075] Template parameter not resolved: invalid application of ‘sizeof’ to incomplete type ‘boost::serialization::U’
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84075 --- Comment #9 from Christoph Hertzberg --- Independent of this issue, the forward declaration in boost/serialization/shared_ptr_helper.hpp does not make sense. I created a PR to fix that: https://github.com/boostorg/serialization/pull/144
[Bug c++/84075] Template parameter not resolved: invalid application of ‘sizeof’ to incomplete type ‘boost::serialization::U’
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84075 Christoph Hertzberg changed: What|Removed |Added CC||chtz at informatik dot uni-bremen. ||de --- Comment #8 from Christoph Hertzberg --- Another case where someone hit this problem: https://stackoverflow.com/questions/54534047/eigen-matrix-boostserialization-c17/ Corresponding Bug at the Eigen-library: http://eigen.tuxfamily.org/bz/show_bug.cgi?id=1676
[Bug c++/87613] New: Non-reachable default required in switch statement to get optimal code
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87613 Bug ID: 87613 Summary: Non-reachable default required in switch statement to get optimal code Product: gcc Version: 7.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: chtz at informatik dot uni-bremen.de Target Milestone: --- Created attachment 44841 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44841=edit Sample code with non-reachable default case Compiling the attached code with -O2 generates a jump-table, which directly contains the `foo()` function addresses. Removing the (non-reachable) `default` case generates an indirect jump-table which jumps to code that first moves the function address into a register and then jumps. In g++-8.x this always generates optimal code, but without the default-case a warning is generated: warning: control reaches end of non-void function [-Wreturn-type] Godbolt-Link (try around with commenting in/out the default or return 0;) https://godbolt.org/z/itpvL6 Directly returning writing this also leads to an indirect jump-table: case X: return foo();
[Bug c++/87503] New: Spurious -Wunused-but-set-variable warning in template function
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87503
Bug ID: 87503
Summary: Spurious -Wunused-but-set-variable warning in template
function
Product: gcc
Version: 8.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: chtz at informatik dot uni-bremen.de
Target Milestone: ---
Using g++ 8.1.0 and compiling the following minimal example with -Wall
template
Index bar(Index rows, Index cols) {
const bool left = flag;
Index x = left ? rows : cols;
return x;
}
int main() {
return bar(1,2);
}
I'm getting this:
warning: variable ‘left’ set but not used [-Wunused-but-set-variable]
This works fine with g++-7.3 (or earlier) and seems to be fixed in 8.2.0 (I
don't have easy access to 8.1.1. If it has been fixed there already, apologies
for the noise)
Maybe related issue: Bug 85827
[Bug libstdc++/81599] New: Error in documentation of std::stack
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81599 Bug ID: 81599 Summary: Error in documentation of std::stack Product: gcc Version: 7.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: libstdc++ Assignee: unassigned at gcc dot gnu.org Reporter: chtz at informatik dot uni-bremen.de Target Milestone: --- I just noticed an error in the documentation of std::stack. It is claimed here: https://gcc.gnu.org/onlinedocs/gcc-7.1.0/libstdc++/api/a01646_source.html#l00087 that the underlying container must support "@c back, @c push_back, and @c pop_front," however, it must of course provide pop_back (instead of pop_front). The error seems to have existed for quite a while, e.g., in version 4.6 is exactly the same paragraph: https://gcc.gnu.org/onlinedocs/gcc-4.6.4/libstdc++/api/a01078_source.html#l00083
[Bug c++/66472] -Wshadow gets confused by using statements in template classes
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66472
Christoph Hertzberg chtz at informatik dot uni-bremen.de changed:
What|Removed |Added
CC||chtz at informatik dot
uni-bremen.
||de
--- Comment #1 from Christoph Hertzberg chtz at informatik dot uni-bremen.de
---
Wouldn't this actually be a valid warning if BaseClass had a constructor taking
a function pointer/member function pointer?
struct BaseClass {
BaseClass(int) { std::cout int\n; }
BaseClass(int () ) { std::cout int()\n; }
BaseClass(int (BaseClass::*)()) {std::cout int (BaseClass::*)()\n; }
static int size() { return 0;}
int size2() { return 0; }
};
struct Foo : public BaseClass {
using BaseClass::size;
using BaseClass::size2;
// size shadows BaseClass::size!
Foo(int size) : BaseClass(size) {}
Foo() : BaseClass(size) {} // uses BaseClass::size
Foo(char) : BaseClass(size2) {} // uses BaseClass::size2
};
[Bug c++/66472] -Wshadow gets confused by using statements in template classes
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66472
--- Comment #6 from Christoph Hertzberg chtz at informatik dot uni-bremen.de
---
Ok, good point on shadowing free functions.
Next pathological example: If you have a template specialization of your Base
with a static member variable called `size`, wouldn't the warning make sense?
template class T
struct Base {
Base(int y) {std::cout y= y \n;}
T size();
};
templateclass T
struct Bar : BaseT {
using BaseT::size;
Bar(int size) : BaseT(size) {}
Bar() : BaseT(size) {} // only works for T==int
};
// Specialization, probably not visible when Bar is defined:
template
struct Baseint {
Baseint(int x) {std::cout x= x \n;}
const static int size=42;
};
[Bug c++/53900] [regression] Too optimistic on a alignment assert
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53900 --- Comment #7 from Christoph Hertzberg chtz at informatik dot uni-bremen.de 2013-01-07 10:19:13 UTC --- (In reply to comment #6) __attribute__((aligned(16))) float array[4]; Explicitly says the array is aligned to 16 bytes which means it is undefined by the C/C++ standard what happens if you a pointer to the struct which contains this array. As this pointer will always be aligned by definition of the struct (and any other use of it is undefined), then by definition std::ptrdiff_t(array) will always have the lower 8bits be zero. So does that mean that new and std::allocator act undefined for aligned objects? Is there anything wrong with Gael's second test case?
[Bug c++/46872] New: 'using' in templated inheritance makes protected member public
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46872 Summary: 'using' in templated inheritance makes protected member public Product: gcc Version: 4.3.2 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassig...@gcc.gnu.org ReportedBy: c...@informatik.uni-bremen.de Hi, I can compile the attached piece of code, which I think is illegal C++. I checked several other compilers which all reject it. Also, the same programm without templates fails in g++ (as expected), too. I'm not sure if this behaviour is somehow intended but it does not seem logical to me at all. Best regards, Christoph
[Bug c++/46872] 'using' in templated inheritance makes protected member public
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46872 --- Comment #1 from Christoph Hertzberg chtz at informatik dot uni-bremen.de 2010-12-09 17:21:37 UTC --- Created attachment 22694 -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=22694 code that should fail to compile
[Bug c++/46872] 'using' in templated inheritance makes protected member public
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46872 Christoph Hertzberg chtz at informatik dot uni-bremen.de changed: What|Removed |Added Resolution|WORKSFORME |FIXED --- Comment #3 from Christoph Hertzberg chtz at informatik dot uni-bremen.de 2010-12-09 18:23:32 UTC --- (In reply to comment #2) Indeed it does, in current 4.5 branch and mainline. 4.3.x is not maintained anymore. Just checked it on a slightly more up-to-date machine, it seems to have been fixed at least in 4.4.1 already. Sorry for the noise.
