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From: "michsteinb at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/105289] New: ICE on partial specialization
Date: Fri, 15 Apr 2022 22:59:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105289

            Bug ID: 105289
           Summary: ICE on partial specialization
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: michsteinb at gmail dot com
  Target Milestone: ---

Created attachment 52818
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D52818&action=3Dedit
Self-contained reproduction of the ICE, compile with -std=3Dc++20

arm-none-eabi-g++ 11.2 crashes on attached self-contained code with followi=
ng
prompt on win64:
```
PS H:\projects\install\arm-embedded-gcc\11.2-2022.02\bin>
.\arm-none-eabi-g++.exe -save-temps -std=3Dc++20 -c repro.cxx
repro.cxx:14:8: internal compiler error: Segmentation fault
   14 | struct push_front_vlist<XList<T, Vs...>, Arg>
      |        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://bugs.linaro.org/> for instructions.
```

The 10.x release cycle compilers accepted this code, so does clang, so this=
 is
a regression introduced with 11.0.

Further checks on godbolt showed the same behaviour on all 11.x compilers I
tried.

The problem stems from the primary template using a meta-function of its fi=
rst
parameter as type for its second. If I do not constrain the type of Arg, the
crash disappears.=