https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124431
Bug ID: 124431
Summary: See incorrect 'error: accessing uninitialised array
element' in C++20 module
Product: gcc
Version: 16.0
URL: https://github.com/sebsjames/mathplot/tree/dev/modules
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: sebj_coder3 at pm dot me
CC: sebj_coder3 at pm dot me
Target Milestone: ---
When building a C++ module, I have a compiler error from g++ (built from
master; gcc16-prerelease) that I don't think is correct. clang++-main (version
23 prerelease) is able to compile the module. g++ versions 13 and 14 compile a
header-only version of the same (or at least, very similar) code.
I am afraid I don't have a minimal example for this problem, but here are steps
to reproduce:
Install some prerequisites. On Ubuntu/Debian it's these:
sudo apt install build-essential git wget \
librapidxml-dev ninja-build \
freeglut3-dev libglu1-mesa-dev libxmu-dev libxi-dev \
libglfw3-dev libfreetype-dev libarmadillo-dev libhdf5-dev
PLUS g++ compiled from master and cmake at least version 3.28.5.
clone mathplot recursively (it has two submodules):
git clone --recurse-submodules [email protected]:sebsjames/mathplot
switch to the dev/modules branch
cd mathplot
git co dev/modules
git submodule update
Build using cmake:
mkdir bgcc
cd bgcc
CC=/path/to/gcc CXX=/path/to/g++ cmake .. -GNinja
ninja helloworld
You should see this error output:
[11:37:39 bgcc] ninja helloworld
[1/2] Building CXX object examples/CMakeFiles/helloworld.dir/helloworld.cpp.o
FAILED: examples/CMakeFiles/helloworld.dir/helloworld.cpp.o
/opt/gcc-master/bin/g++ -I/home/seb/src/mathplot -I/usr/include/hdf5/serial
-I/home/seb/src/mathplot/maths -I/home/seb/src/mathplot/json/include
-I/home/seb/src/mathplot/include/rapidxml-1.13 -isystem /usr/include/freetype2
-g -Wall -Wextra -Wpedantic -pedantic-errors -Werror -Wfatal-errors -Wno-psabi
-O3 -fconstexpr-ops-limit=5000000000 -DMPLOT_HAVE_STD_FORMAT -fopenmp
-DMPLOT_FONTS_DIR="\"/home/seb/src/mathplot/fonts\"" -std=c++20 -MD -MT
examples/CMakeFiles/helloworld.dir/helloworld.cpp.o -MF
examples/CMakeFiles/helloworld.dir/helloworld.cpp.o.d -fmodules-ts
-fmodule-mapper=examples/CMakeFiles/helloworld.dir/helloworld.cpp.o.modmap -MD
-fdeps-format=p1689r5 -x c++ -o
examples/CMakeFiles/helloworld.dir/helloworld.cpp.o -c
/home/seb/src/mathplot/examples/helloworld.cpp
In module sm.mat, imported at /home/seb/src/mathplot/mplot/VisualCommon.h:20,
of module mplot.visualcommon, imported at
/home/seb/src/mathplot/mplot/VisualResources.h:35,
of module mplot.visualresources, imported at
/home/seb/src/mathplot/mplot/Visual.h:34,
of module mplot.visual, imported at
/home/seb/src/mathplot/examples/helloworld.cpp:1:
/home/seb/src/mathplot/maths/sm/mat: In instantiation of ‘void
mplot::[email protected]<glver>::computeSceneview_for_follower()
[with int glver = 262145]’:
/home/seb/src/mathplot/mplot/VisualOwnable.h:1245:23: required from ‘void
mplot::[email protected]<glver>::computeSceneview() [with int
glver = 262145]’
1245 | this->computeSceneview_for_follower();
| ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/seb/src/mathplot/mplot/VisualOwnable.h:427:19: required from ‘void
mplot::[email protected]<glver>::render() [with int glver =
262145]’
427 | this->computeSceneview();
| ~~~~~~^~~~~~~~~~~~~~~~
/home/seb/src/mathplot/mplot/Visual.h:179:29: required from ‘void
mplot::[email protected]<glver>::keepOpen() [with int glver = 262145]’
179 | this->render();
| ~~~~~~~~~~~~^~
/home/seb/src/mathplot/examples/helloworld.cpp:8:15: required from here
8 | v.keepOpen();
| ~~~~~~~~~~^~
/home/seb/src/mathplot/mplot/VisualOwnable.h:1232:64: in ‘constexpr’
expansion of
‘mplot::[email protected]<262145>::rotate_about_y()’
1232 | constexpr sm::mat<float, 4> rotn_y = rotate_about_y();
| ~~~~~~~~~~~~~~^~
/home/seb/src/mathplot/mplot/VisualOwnable.h:1175:22: in ‘constexpr’
expansion of ‘r.sm::[email protected]<float, 4>::rotate<>(sm::[email protected]<float,
3>{std::array<float, 3>{std::__array_traits<float, 3>::_Type{0.0f, 1.0e+0f}}},
sm::mathconst<float>::pi)’
1175 | r.rotate (sm::vec<>::uy(), sm::mathconst<float>::pi);
| ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/seb/src/mathplot/maths/sm/mat:924:29: in ‘constexpr’ expansion of
‘((sm::[email protected]<float, 4>*)this)->sm::[email protected]<float,
4>::rotate<float>(q)’
924 | this->rotate<T> (q);
| ~~~~~~~~~~~~~~~~^~~
/home/seb/src/mathplot/maths/sm/mat:881:77: in ‘constexpr’ expansion of
‘((sm::[email protected]<float, 4>*)this)->sm::[email protected]<float,
4>::operator*=<float,
4, 4>(sm::[email protected]<float, 4>::pure_rotation<float>((* & q)))’
881 | constexpr void rotate (const sm::quaternion<T>& q) noexcept {
*this *= this->pure_rotation (q); }
|
~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
/home/seb/src/mathplot/maths/sm/mat:1240:64: error: accessing uninitialised
array element
1240 | m[0] = this->arr[0] * m2.arr[0] + this->arr[4] *
m2.arr[1] + this->arr[8] * m2.arr[2] + this->arr[12] * m2.arr[3];
|
~~~~~~~~~~~~~^~~~~~~~~
compilation terminated due to -Wfatal-errors.
ninja: build stopped: subcommand failed.
Expected behaviour: The program to compile.
Hope this helps C++ module development.
