Bug#1135970: performance regression when compiling linux-7.0.4 with gcc-16-20260425-1

Package: gcc-16
Version: 16-20260425-1
Severity: normal
X-Debbugs-Cc: [email protected]




-- System Information:
Debian Release: forky/sid
  APT prefers unstable
  APT policy: (1001, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 7.1.0-rc2-next-20260506-master (SMP w/32 CPU threads; PREEMPT)
Locale: LANG=de_DE.UTF-8, LC_CTYPE=C.UTF-8 (charmap=locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: unable to detect

Versions of packages gcc-16 depends on:
ii  binutils                 2.46-3
ii  cpp-16                   16-20260425-1
ii  gcc-16-base              16-20260425-1
ii  gcc-16-x86-64-linux-gnu  16-20260425-1

Versions of packages gcc-16 recommends:
ii  libc6-dev  2.42-16

Versions of packages gcc-16 suggests:
pn  gcc-16-doc       <none>
pn  gcc-16-locales   <none>
pn  gcc-16-multilib  <none>

-- debconf information excluded

When compiling linux-7.0.4 with module (allmodconfig) gcc-16 takes
~18.5min, while using gcc-{14.15} only takes ~11.25min.

Steps to reproduce:
1. Unpack linux-7.0.4.tar.xz (from kernel.org)
2. Apply this patch (otherwise compilation with gcc-16 fails)
https://lore.kernel.org/all/[email protected]/
3. Either install gcc from experimental or point the /usr/bin/{gcc,cpp}
symlinks to {gcc,cpp}-16 (using CC=gcc-16 does not work)
4. Compile with
$ make allmodconfig
$ time LANG=C make -j32
5. Wait for more than 18 minutes

A test with gcc-16.1.1 20260430 (in a cachyos chroot) shows no
performancee regression when compiling linux-7.0.4.

Bert Karwatzki