[llvm][test][NFCI] Use absolute build path instead of a relative path

[tambry]

Scoping to the root build directory instead of using the path directly is awkward and the only such occurrence in the test suite. Pass the appropriate substitution instead for this.

Background
In my downstream %llvmshlibdir is much more nested so the single ../ is insufficient.
But we can use a much more direct substitution rather than a round-about way, which is both cleaner and avoids me needing to patch this test.

[jh7370]

I don't think it's a good idea for me to review this. I've added some other reviewers, who reviewed the original PR that introduced the PR. Also pinging @Tcc100, since they were the one to originally introduce the test.

[arsenm]

I suppose this is only an issue because the plugin library is built into unittests, and not lib? The other sample plugin binaries just go to the ordinary lib directory

[tambry]

@arsenm Correct. The other sample plugins don't have any llc tests that manually -load the plugin and run unittests. So this is the only test where both need to work.

But I had another look now and managed to simplify this further. We can actually put the plugin into lib and just rely on the RPATH for it to be found. It's marked BUILDTREE_ONLY so it won't get installed and there seem to be other tests that rely on this too. I think PluginsTest.cpp, which the existing code was likely copy-paste from, could be simplified similarly, but I'll leave that as a follow-up.

[mgorny]

This change introduced test failures for me:

FAIL: LLVM :: Other/codegen-plugin-loading.ll (41910 of 62452)
******************** TEST 'LLVM :: Other/codegen-plugin-loading.ll' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
/var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm_build-.arm64/bin/llc -load %llvm_obj_root/unittests/CodeGen/CGPluginTest/CGTestPlugin.so /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm/test/Other/codegen-plugin-loading.ll -o - | /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm_build-.arm64/bin/FileCheck /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm/test/Other/codegen-plugin-loading.ll
# executed command: /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm_build-.arm64/bin/llc -load %llvm_obj_root/unittests/CodeGen/CGPluginTest/CGTestPlugin.so /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm/test/Other/codegen-plugin-loading.ll -o -
# .---command stderr------------
# | Error opening '%llvm_obj_root/unittests/CodeGen/CGPluginTest/CGTestPlugin.so': %llvm_obj_root/unittests/CodeGen/CGPluginTest/CGTestPlugin.so: cannot open shared object file: No such file or directory
# |   -load request ignored.
# `-----------------------------
# executed command: /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm_build-.arm64/bin/FileCheck /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm/test/Other/codegen-plugin-loading.ll
# .---command stderr------------
# | /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm/test/Other/codegen-plugin-loading.ll:4:10: error: CHECK: expected string not found in input
# | ; CHECK: CodeGen Test Pass running on main
# |          ^
# | <stdin>:1:1: note: scanning from here
# |  .file "codegen-plugin-loading.ll"
# | ^
# | <stdin>:3:12: note: possible intended match here
# |  .globl main // -- Begin function main
# |            ^
# | 
# | Input file: <stdin>
# | Check file: /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm/test/Other/codegen-plugin-loading.ll
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |            1:  .file "codegen-plugin-loading.ll" 
# | check:4'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
# |            2:  .text 
# | check:4'0     ~~~~~~~
# |            3:  .globl main // -- Begin function main 
# | check:4'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# | check:4'1                ?                            possible intended match
# |            4:  .p2align 2 
# | check:4'0     ~~~~~~~~~~~~
# |            5:  .type main,@function 
# | check:4'0     ~~~~~~~~~~~~~~~~~~~~~~
# |            6: main: // @main 
# | check:4'0     ~~~~~~~~~~~~~~~
# |            7:  .cfi_startproc 
# | check:4'0     ~~~~~~~~~~~~~~~~
# |            8: // %bb.0: 
# | check:4'0     ~~~~~~~~~~
# |            .
# |            .
# |            .
# | >>>>>>
# `-----------------------------
# error: command failed with exit status: 1

--

********************

My educated guess is that %llvm_obj_root is not in config.substitutions.

[tambry]

@mgorny Seems I forgot to revert one of the substitution changes while rebasing locally. Will fix promptly: #159914.

[mgorny]

This path still seems wrong:

# | Error opening '/var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm_build-.arm64/lib64/unittests/CodeGen/CGPluginTest/CGTestPlugin.so': /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm_build-.arm64/lib64/unittests/CodeGen/CGPluginTest/CGTestPlugin.so: cannot open shared object file: No such file or directory

I'm seeing:

# find /var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm_build-.arm64 -name CGTestPlugin.so
/var/tmp/portage/llvm-core/llvm-22.0.0.9999/work/llvm_build-.arm64/lib64/CGTestPlugin.so

[tambry]

@mgorny That's what I get for not waiting my local build and test run to finish... Finally fixed: #159923. 🤞

[mgorny]

Yeah, I can confirm it passes now.