https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86091
Bug ID: 86091 Summary: [fold expression] Slow compile time and high memory usage compared to initializer_list folds Product: gcc Version: 7.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: vasili.burdo at gmail dot com Target Milestone: --- Created attachment 44253 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44253&action=edit Test program Consider test program in attachment. This program tries to validate large (1000 entries) user-defined literal using c++17 fold expression - and its compile time is VERY slow. For c++ version earlier than c++17 fold is emulated using intitalizer_list - in this case compile time is MUCH better. Please note execution times and memory usage reported by `time' in invocation examples below. When compiled with command line (buggy behavior) "/usr/bin/time -v g++ -std=gnu++1z -Wall -Wextra -D BUG test.cpp" its output is: ---------------------------------------------------------- Command being timed: "g++ -std=gnu++1z -Wall -Wextra -D BUG test.cpp" User time (seconds): 30.40 System time (seconds): 1.72 Percent of CPU this job got: 99% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:32.12 Average shared text size (kbytes): 0 Average unshared data size (kbytes): 0 Average stack size (kbytes): 0 Average total size (kbytes): 0 Maximum resident set size (kbytes): 6760368 Average resident set size (kbytes): 0 Major (requiring I/O) page faults: 0 Minor (reclaiming a frame) page faults: 1690547 Voluntary context switches: 13 Involuntary context switches: 42 Swaps: 0 File system inputs: 0 File system outputs: 136 Socket messages sent: 0 Socket messages received: 0 Signals delivered: 0 Page size (bytes): 4096 Exit status: 0 ---------------------------------------------------------- When compiled with command line (no `BUG' defined) "/usr/bin/time -v g++ -std=gnu++1z -Wall -Wextra test.cpp" its output is: ---------------------------------------------------------- Command being timed: "g++ -std=gnu++1z -Wall -Wextra test.cpp" User time (seconds): 0.14 System time (seconds): 0.02 Percent of CPU this job got: 99% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.16 Average shared text size (kbytes): 0 Average unshared data size (kbytes): 0 Average stack size (kbytes): 0 Average total size (kbytes): 0 Maximum resident set size (kbytes): 47784 Average resident set size (kbytes): 0 Major (requiring I/O) page faults: 0 Minor (reclaiming a frame) page faults: 13603 Voluntary context switches: 12 Involuntary context switches: 5 Swaps: 0 File system inputs: 0 File system outputs: 880 Socket messages sent: 0 Socket messages received: 0 Signals delivered: 0 Page size (bytes): 4096 Exit status: 0 ---------------------------------------------------------- Compiler version (official Ubuntu GCC): ---------------------------------------------------------- Using built-in specs. COLLECT_GCC=g++ COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/7/lto-wrapper OFFLOAD_TARGET_NAMES=nvptx-none OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 7.3.0-16ubuntu3' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --with-as=/usr/bin/x86_64-linux-gnu-as --with-ld=/usr/bin/x86_64-linux-gnu-ld --program-suffix=-7 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix gcc version 7.3.0 (Ubuntu 7.3.0-16ubuntu3) ---------------------------------------------------------- OS Version: ---------------------------------------------------------- Linux epbyminw0019t2 4.15.0-22-generic #24-Ubuntu SMP Wed May 16 12:15:17 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux ---------------------------------------------------------- I tried multiple GCC versions starting from 5.3 to 8.0.0 on Ubuntu and Windows (MINGW) all of them have the same problem.