[Bug target/98361] New: L1/L2 cache characteristics not recognized with -mtune=znver2

["sdack at gmx dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98361

            Bug ID: 98361
           Summary: L1/L2 cache characteristics not recognized with
                    -mtune=znver2
           Product: gcc
           Version: 10.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sdack at gmx dot com
  Target Milestone: ---

Hello,

I've come across an unexpected behaviour of gcc and wanted to ask for
help. I've noticed that when I specify '-march=znver2' does gcc use the
incorrect values for the L1/L2 cache. Only when '-march=native' was used
and gcc detected the CPU at run-time does it use the correct values. For
example on a Ryzen 7 3800X (a Zen 2 CPU):

$ gcc -march=znver2 --help=params -Q|fgrep cache
  --param=l1-cache-line-size=         32
  --param=l1-cache-size=              64
  --param=l2-cache-size=              512

versus:

$ gcc -march=native --help=params -Q|fgrep cache
  --param=l1-cache-line-size=         64
  --param=l1-cache-size=              32
  --param=l2-cache-size=              512

GCC does detect the CPU as 'znver2':

$ gcc -march=native --help=target -Q|fgrep march
  -march=                             znver2

I've also verified this behaviour with '-mtune=znver2', and again does
GCC only use the correct values when it uses auto-detection.

Why does GCC not use the correct L1/L2 cache values when '-march=znver2'
or '-mtune=znver2' is specified?

Sven

PS: I've now also checked parts of the gcc source code and
gcc/config/i386/x86-tune-costs.h (around line 1557) does hold the correct
values and it appears these only don't get used somehow.