ppc64le: failing tests/debuginfo/opt/dead_refs

[blkerby]

On powerpc64le-unknown-linux-gnu, with $ ./x test debuginfo I'm getting this error:

failures:

---- [debuginfo-gdb] tests/debuginfo/opt/dead_refs.rs stdout ----
NOTE: compiletest thinks it is using GDB version 17001000
------gdb stdout------------------------------
GNU gdb (Ubuntu 17.1-2ubuntu1) 17.1
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Breakpoint 1 at 0xa00: file tests/debuginfo/opt/dead_refs.rs, line 46.

This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.ubuntu.com>
Enable debuginfod for this session? (y or [n]) [answered N; input not from terminal]
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/powerpc64le-linux-gnu/libthread_db.so.1".

Breakpoint 1, dead_refs::test_ref (ref_foo=0x7fffffffe8f8) at tests/debuginfo/opt/dead_refs.rs:46
46	}

------gdb stderr------------------------------
warning: File "/home/ubuntu/rustc-nightly-src/src/etc/gdb_load_rust_pretty_printers.py" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
/home/ubuntu/rustc-nightly-src/build/powerpc64le-unknown-linux-gnu/test/debuginfo/opt/dead_refs.gdb/dead_refs.debugger.script:9: Error in sourced command file:
No symbol 'ref_v0' in current context

------------------------------------------

error: gdb failed to execute
status: exit status: 1
command: PYTHONPATH="/home/ubuntu/rustc-nightly-src/src/etc" "/usr/bin/gdb" "-quiet" "-batch" "-nx" "-command=/home/ubuntu/rustc-nightly-src/build/powerpc64le-unknown-linux-gnu/test/debuginfo/opt/dead_refs.gdb/dead_refs.debugger.script"
--- stdout -------------------------------
GNU gdb (Ubuntu 17.1-2ubuntu1) 17.1
Copyright (C) 2025 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "powerpc64le-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word".
To enable execution of this file add
	add-auto-load-safe-path /home/ubuntu/rustc-nightly-src/src/etc/gdb_load_rust_pretty_printers.py
line to your configuration file "/home/ubuntu/.config/gdb/gdbinit".
To completely disable this security protection add
	set auto-load safe-path /
line to your configuration file "/home/ubuntu/.config/gdb/gdbinit".
For more information about this security protection see the
"Auto-loading safe path" section in the GDB manual.  E.g., run from the shell:
	info "(gdb)Auto-loading safe path"
Breakpoint 1 at 0xa00: file tests/debuginfo/opt/dead_refs.rs, line 46.

This GDB supports auto-downloading debuginfo from the following URLs:
  <https://debuginfod.ubuntu.com>
Enable debuginfod for this session? (y or [n]) [answered N; input not from terminal]
Debuginfod has been disabled.
To make this setting permanent, add 'set debuginfod enabled off' to .gdbinit.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/powerpc64le-linux-gnu/libthread_db.so.1".

Breakpoint 1, dead_refs::test_ref (ref_foo=0x7fffffffe8f8) at tests/debuginfo/opt/dead_refs.rs:46
46	}
------------------------------------------
--- stderr -------------------------------
warning: File "/home/ubuntu/rustc-nightly-src/src/etc/gdb_load_rust_pretty_printers.py" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
/home/ubuntu/rustc-nightly-src/build/powerpc64le-unknown-linux-gnu/test/debuginfo/opt/dead_refs.gdb/dead_refs.debugger.script:9: Error in sourced command file:
No symbol 'ref_v0' in current context
------------------------------------------

---- [debuginfo-gdb] tests/debuginfo/opt/dead_refs.rs stdout end ----

failures:
    [debuginfo-gdb] tests/debuginfo/opt/dead_refs.rs

test result: FAILED. 152 passed; 1 failed; 20 ignored; 0 measured; 0 filtered out; finished in 15.34s

[helce]

I've got the same problem. Made some investigation, reason is sext/zext loads during extension of 32-bit value to 64-bit g8rc register overwrites debug-location, same for sext/zext for return values in sparc64.

It is DAG->DAG Pattern Instruction Selection in llvm.

For example, check same load on powerpc and powerpc64

powerpc:
%1:gprc = LWZ 8, %0:gprc_and_gprc_nor0, debug-location !187 :: (dereferenceable load (s32) from %ir.0, align 8); dead_refs.rs:45:5

powerpc64:
%1:g8rc = LWZ8 8, %0:g8rc_and_g8rc_nox0, debug-location !188 :: (dereferenceable load (s32) from %ir.0, align 8); dead_refs.rs:46:2

Debug-location changes the line from dead_refs.rs:45 to dead_refs.rs:46.
But dead_refs.rs:46 is out of scope for checking refs, so test fails.
Looks like this test should be ignored for powerpc64, sparc64

[helce]

Can be fixed by specifying explicit integer args extension, like in #131955 via compute_rust_abi_info.