https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103631
Bug ID: 103631
Summary: Internal compiler error in C++20 class NTTP + concept
Product: gcc
Version: 11.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: winmikedows at hotmail dot com
Target Milestone: ---
I am using GCC 11.2.0 on macOS 10.15.7, and it throw ICE on the following code
snippet:
```cpp
// value_specialize, work with NTTP only
template<typename Target, template<auto> typename T>
inline constexpr bool is_specialize_value_v = false;
template<template<auto> typename T, auto Ts>
inline constexpr bool is_specialize_value_v<T<Ts>, T> = true;
template<typename Target, template<auto> typename T>
concept specialize_value = is_specialize_value_v<Target, T>;
template<int i> struct Test{};
template<Test str>
struct A
{
template<typename T> requires specialize_value<T, A>
int fun(T&&)
{
return 1;
}
};
```
The full compiler output of my invocation `g++-11 -v -save-temps -O0 -std=c++20
-Wall -Wextra -o code code.cpp` is (The intermediate file code.ii is identical
to code.cpp except some #-directives since I'm not using the preprocessor, and
code.s is empty, so I will not include them)
```
Using built-in specs.
COLLECT_GCC=g++-11
COLLECT_LTO_WRAPPER=/usr/local/Cellar/gcc/11.2.0_3/libexec/gcc/x86_64-apple-darwin19/11/lto-wrapper
Target: x86_64-apple-darwin19
Configured with: ../configure --prefix=/usr/local/Cellar/gcc/11.2.0_3
--libdir=/usr/local/Cellar/gcc/11.2.0_3/lib/gcc/11 --disable-nls
--enable-checking=release --with-gcc-major-version-only
--enable-languages=c,c++,objc,obj-c++,fortran,d --program-suffix=-11
--with-gmp=/usr/local/opt/gmp --with-mpfr=/usr/local/opt/mpfr
--with-mpc=/usr/local/opt/libmpc --with-isl=/usr/local/opt/isl
--with-zstd=/usr/local/opt/zstd --with-pkgversion='Homebrew GCC 11.2.0_3'
--with-bugurl=https://github.com/Homebrew/homebrew-core/issues
--enable-libphobos --build=x86_64-apple-darwin19 --with-system-zlib
--disable-multilib --with-native-system-header-dir=/usr/include
--with-sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (Homebrew GCC 11.2.0_3)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O0' '-std=c++20' '-Wall' '-Wextra'
'-o' 'code' '-mmacosx-version-min=10.15.0' '-asm_macosx_version_min=10.15'
'-shared-libgcc' '-mtune=core2'
/usr/local/Cellar/gcc/11.2.0_3/libexec/gcc/x86_64-apple-darwin19/11/cc1plus -E
-quiet -v -D__DYNAMIC__ code.cpp -fPIC -mmacosx-version-min=10.15.0
-mtune=core2 -std=c++20 -Wall -Wextra -O0 -fpch-preprocess -o code.ii
ignoring nonexistent directory
"/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/local/include"
ignoring nonexistent directory
"/usr/local/Cellar/gcc/11.2.0_3/lib/gcc/11/gcc/x86_64-apple-darwin19/11/../../../../../../x86_64-apple-darwin19/include"
ignoring nonexistent directory
"/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
/usr/local/Cellar/gcc/11.2.0_3/lib/gcc/11/gcc/x86_64-apple-darwin19/11/../../../../../../include/c++/11
/usr/local/Cellar/gcc/11.2.0_3/lib/gcc/11/gcc/x86_64-apple-darwin19/11/../../../../../../include/c++/11/x86_64-apple-darwin19
/usr/local/Cellar/gcc/11.2.0_3/lib/gcc/11/gcc/x86_64-apple-darwin19/11/../../../../../../include/c++/11/backward
/usr/local/Cellar/gcc/11.2.0_3/lib/gcc/11/gcc/x86_64-apple-darwin19/11/include
/usr/local/Cellar/gcc/11.2.0_3/lib/gcc/11/gcc/x86_64-apple-darwin19/11/include-fixed
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include
/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/System/Library/Frameworks
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-O0' '-std=c++20' '-Wall' '-Wextra'
'-o' 'code' '-mmacosx-version-min=10.15.0' '-asm_macosx_version_min=10.15'
'-shared-libgcc' '-mtune=core2'
/usr/local/Cellar/gcc/11.2.0_3/libexec/gcc/x86_64-apple-darwin19/11/cc1plus
-fpreprocessed code.ii -fPIC -quiet -dumpbase code.cpp -dumpbase-ext .cpp
-mmacosx-version-min=10.15.0 -mtune=core2 -O0 -Wall -Wextra -std=c++20 -version
-o code.s
GNU C++20 (Homebrew GCC 11.2.0_3) version 11.2.0 (x86_64-apple-darwin19)
compiled by GNU C version 11.2.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++20 (Homebrew GCC 11.2.0_3) version 11.2.0 (x86_64-apple-darwin19)
compiled by GNU C version 11.2.0, GMP version 6.2.1, MPFR version
4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: c8ad714ab17745b5fe60039e428beb58
code.cpp:14:35: internal compiler error: in unify, at cp/pt.c:23587
14 | template<typename T> requires specialize_value<T, A>
| ^~~~~~~~~~~~~~~~~~~~~~
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://github.com/Homebrew/homebrew-core/issues> for instructions.
```
I can also reproduce the behavior in godbolt on GCC trunk:
https://godbolt.org/z/bxeYvdezP, and clang++ pass with the code, so I think
this code is valid.
BTW, I also tried altering the code, and found that if you do any one of the
four things below, GCC will pass with it.
1. change line 6 to use `template<int>` instead of `template<auto>`
2. change line 9 to remove template and just use `struct Test{}`
3. change line 11 to use any other type of NTTP (like `int`)
4. change line 14 to use `is_specialize_value_v` instead of `specialize_value`
So probably this ICE is just the result of code complexity.
