https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95029
Bug ID: 95029
Summary: Compile error when using constant variable instead of
literal
Product: gcc
Version: 10.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: maxi.matthe at googlemail dot com
Target Milestone: ---
Created attachment 48494
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48494&action=edit
Original source file triggering the bug.
With the attached cpp-file, a strange behaviour is triggered. Tested with
g++-10.1 built with docker (docker run gcc:10.1). The bug is also present in
g++-7.5.0.
Upon compiling the attached source file, this output is obtained:
=====
# g++ -v -c -Wall -Wextra -fno-strict-aliasing -fwrapv
-fno-aggressive-loop-optimizations -save-temps test_fragmentation.cpp
Using built-in specs.
COLLECT_GCC=g++
Target: x86_64-linux-gnu
Configured with: /usr/src/gcc/configure --build=x86_64-linux-gnu
--disable-multilib --enable-languages=c,c++,fortran,go
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.1.0 (GCC)
COLLECT_GCC_OPTIONS='-v' '-c' '-Wall' '-Wextra' '-fno-strict-aliasing'
'-fwrapv' '-fno-aggressive-loop-optimizations' '-save-temps' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
/usr/local/libexec/gcc/x86_64-linux-gnu/10.1.0/cc1plus -E -quiet -v
-imultiarch x86_64-linux-gnu -D_GNU_SOURCE test_fragmentation.cpp
-mtune=generic -march=x86-64 -Wall -Wextra -fno-strict-aliasing -fwrapv
-fno-aggressive-loop-optimizations -fpch-preprocess -o test_fragmentation.ii
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/local/lib/gcc/x86_64-linux-gnu/10.1.0/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/lib/gcc/x86_64-linux-gnu/10.1.0/../../../../include/c++/10.1.0
/usr/local/lib/gcc/x86_64-linux-gnu/10.1.0/../../../../include/c++/10.1.0/x86_64-linux-gnu
/usr/local/lib/gcc/x86_64-linux-gnu/10.1.0/../../../../include/c++/10.1.0/backward
/usr/local/lib/gcc/x86_64-linux-gnu/10.1.0/include
/usr/local/include
/usr/local/lib/gcc/x86_64-linux-gnu/10.1.0/include-fixed
/usr/include/x86_64-linux-gnu
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-c' '-Wall' '-Wextra' '-fno-strict-aliasing'
'-fwrapv' '-fno-aggressive-loop-optimizations' '-save-temps' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
/usr/local/libexec/gcc/x86_64-linux-gnu/10.1.0/cc1plus -fpreprocessed
test_fragmentation.ii -quiet -dumpbase test_fragmentation.cpp -mtune=generic
-march=x86-64 -auxbase test_fragmentation -Wall -Wextra -version
-fno-strict-aliasing -fwrapv -fno-aggressive-loop-optimizations -o
test_fragmentation.s
GNU C++14 (GCC) version 10.1.0 (x86_64-linux-gnu)
compiled by GNU C version 10.1.0, GMP version 6.1.0, MPFR version
3.1.4, MPC version 1.0.3, isl version isl-0.18-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++14 (GCC) version 10.1.0 (x86_64-linux-gnu)
compiled by GNU C version 10.1.0, GMP version 6.1.0, MPFR version
3.1.4, MPC version 1.0.3, isl version isl-0.18-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 731fbf5b63dd31db9f4b6aef8d6447dc
test_fragmentation.cpp: In function 'void X()':
test_fragmentation.cpp:45:8: error: request for member 'popFragment' in 'frag',
which is of non-class type 'PacketFragmenting(MaxPacketSize, PhySize)' {aka
'PacketFragmenting(NamedType<long unsigned int, MaxPacketSize_t>,
NamedType<long unsigned int, PhySize_t>)'}
45 | frag.popFragment();
| ^~~~~~~~~~~
test_fragmentation.cpp:37:16: warning: unused variable 'PHY_SIZE'
[-Wunused-variable]
37 | const size_t PHY_SIZE = 112;
| ^~~~~~~~
test_fragmentation.cpp:38:16: warning: unused variable 'MAX_PACKET_SIZE'
[-Wunused-variable]
38 | const size_t MAX_PACKET_SIZE = 1500;
| ^~~~~~~~~~~~~~~
root@2580b215cc3e:/app/arm_apps/src/tests/bug#
====
Within the source file, there is a commented-out line. If I uncomment it, i.e.
switch from
const size_t PHY_SIZE = 112;
PacketFragmenting frag(MaxPacketSize(MAX_PACKET_SIZE), PhySize(PHY_SIZE));
to
PacketFragmenting frag(MaxPacketSize(MAX_PACKET_SIZE),
PhySize(static_cast<size_t>(112)));
the file compiles successfully.
To me this seems like a bug, because it should make no difference if I use the
const or the literal.
