[profile][test] Add -fuse-ld=bfd to make instrprof-lto-pgogen.c robust

[MaskRay]

Summary

Otherwise if 'ld' is an older system LLD (FreeBSD; or if someone adds 'ld' to
point to an LLD from a different installation) which does not support the
current ModuleSummaryIndex::BitCodeSummaryVersion, the test will fail.

Add lit feature 'binutils_lto'. GNU ld is more common than GNU gold, so
we can just require 'is_binutils_lto_supported' to additionally support GNU ld.

[myhsu]

According your problem statement, I think the correct way to approach it is to fix the environment (i.e. use the correct version of LLD) because apparently the root of cause is outdated linkers. In other words, your original argument can be extrapolated to outdated GNU as, outdated objdump, or even outdated shell. But I don't think it's a good idea to put version constrains on every of these items, or say "because it's possible that users are using an old version of bash shell, so let's use sh shell"

Also, I'm not sure if this test will work on platform that doesn't have BFD linker at all (e.g. Mac OSX). Although my original patch was fixing a problem targeting BFD linkers, but the original test (i.e. the one without -fuse-ld=bfd) will run on platforms (MSVC will fail but it's not caused by not finding a proper linker) regardless of what the system linker is, because the driver will handle that. But I'm worry that if you explicitly assign the linker to use, platforms without BFD linker will unable to fulfill your linker requirement and fail at the very early stage.

[MaskRay]

In D84133#2162498, @myhsu wrote:

According your problem statement, I think the correct way to approach it is to fix the environment (i.e. use the correct version of LLD) because apparently the root of cause is outdated linkers.

I don't agree with your statement. If you look at various UNSUPPORTED: XFAIL: changes to compiler-rt/test/, many changes are due to reasonable environment differences. On FreeBSD, /usr/bin/ld is a system LLD of an older version.

In other words, your original argument can be extrapolated to outdated GNU as, outdated objdump, or even outdated shell. But I don't think it's a good idea to put version constrains on every of these items, or say "because it's possible that users are using an old version of bash shell, so let's use sh shell"

That is why we can't use objdump, GNU as, readelf, etc. Instead, we use llvm-objdump, llvm-mc and llvm-readelf. I picked -fuse-ld=bfd because I saw -fuse-ld=gold which is already used in a few tests.

Also, I'm not sure if this test will work on platform that doesn't have BFD linker at all (e.g. Mac OSX). Although my original patch was fixing a problem targeting BFD linkers, but the original test (i.e. the one without -fuse-ld=bfd) will run on platforms (MSVC will fail but it's not caused by not finding a proper linker) regardless of what the system linker is, because the driver will handle that. But I'm worry that if you explicitly assign the linker to use, platforms without BFD linker will unable to fulfill your linker requirement and fail at the very early stage.

That was actually my original complaint. The test should be restricted to a few platforms where it makes sense.

[MaskRay]

REQUIRES linux

[arichardson]

compiler-rt/test/profile/instrprof-lto-pgogen.c

1

I wonder if this should be using a new REQUIRES: ld.bfd feature instead of assuming Linux means fuse-ld=bfd will work?

[myhsu]

compiler-rt/test/profile/instrprof-lto-pgogen.c

1

I think that's a good idea, it can solve many debates we discussed here

[MaskRay]

Add binutils_lto

[myhsu]

compiler-rt/test/lit.common.cfg.py

447 ↗

(On Diff #279583)

I think this line is redundant (duplicate with line 461)

[MaskRay]

Delete config.available_features.add('lto')

[myhsu]

Thank you!
LGTM

[MaskRay]

Fix a typo

compiler-rt/test/profile/instrprof-lto-pgogen.c

-// REQUIRES: lto
-// XFAIL: msvc
+// REQUIRES: linux, lto
 
-// RUN: %clang_pgogen=%t.profraw -flto %s -o %t
+// RUN: %clang_pgogen=%t.profraw -fuse-ld=bfd -flto %s -o %t
 // RUN: %run %t
 // RUN: llvm-profdata merge %t.profraw -o %t.profdata
 // RUN: llvm-profdata show %t.profdata | FileCheck %s
 
-// Testing a bug that happens when trying to generate IR
-// profile with BFD linker + LTO plugin
+// Test that we work around https://sourceware.org/bugzilla/show_bug.cgi?id=26262
+// which happens when trying to generate IR profile with BFD linker + LTO plugin.
 
 // CHECK: Instrumentation level: IR
 int main() { return 0; }