SPARC -target-feature +vis breaks flang build on Linux/sparc64

[rorth]

A 2-stage build with flang included is currently broken on Linux/sparc64 with tons of errors like

error: current translation unit is compiled with the target feature '+vis' but the AST file 'tools/flang/lib/Parser/CMakeFiles/FortranParser.dir/cmake_pch.hxx.pch' was not

I could trace this to the fact that the object file creating is run with clang-21 -cc1 -triple sparc64-unknown-linux-gnu -emit-obj -target-feature +vis while the pch generation uses clang-21 -cc1 -triple sparc64-unknown-linux-gnu -emit-pch without the -target-feature +vis, thus the inconsistency.

Even without flang, there are three testsuite regressions showing the same error:

  Clang :: ClangScanDeps/modules-symlink.c
  Clang :: ClangScanDeps/prebuilt-modules-in-stable-dirs.c
  Clang :: SemaCXX/warn-unused-local-typedef-serialize.cpp

While I managed to get further along with the attached preliminary patch, which adds the missing option for -emit-pch and -emit-llvm (which fixes the flang build), this introduces tons of new regressions instead:

  Clang :: ClangScanDeps/module-format.c
  Clang :: ClangScanDeps/modules-pch-common-submodule.c
  Clang :: ClangScanDeps/modules-pch-common-via-submodule.c
  Clang :: ClangScanDeps/modules-pch-dangling.c
  Clang :: ClangScanDeps/modules-pch-imports.c
  Clang :: ClangScanDeps/modules-pch.c
  Clang :: ClangScanDeps/optimize-vfs-pch.m
  Clang :: Index/pch-with-errors.c
  Clang :: PCH/different-diagnostic-level.c
  Clang :: PCH/gch-probe.c
  Clang :: PCH/pch-dir.c
  Clang :: Tooling/pch.cpp

Now the .pch files are correctly built with -target-feature +vis, but the TUs are claimed to be not and I have no idea what's going on.

Fortunately, Solaris/sparcv9 isn't affected because for unknown reasons commit 3853116, which introduced -target-feature +vis, doesn't pass that option on Solaris.

It seems other targets are less affected because unlike the sparcv9 case they only enable -target-feature with special flags and not in general.

[rorth]

@s-barannikov , @MaskRay , @brad0 Any suggestions on how to tackle this?

[rorth]

Patch I've been testing with some success: clv.patch.txt

[koachan]

Fortunately, Solaris/sparcv9 isn't affected because for unknown reasons commit 3853116, which introduced -target-feature +vis, doesn't pass that option on Solaris.

Adding more context, this is because on the OSes listed in the commit (FreeBSD, OpenBSD, Linux), GCC enables VIS by default, and I turned it on to match GCC behavior (a similar treatment is already implemented for external assembler calls - -Av9a being the flag that enables VIS in the assembler -, and is depended on by e.g OpenBSD).

I suppose a proper fix would involve enabling VIS unconditionally throughout LLVM when targeting those OSes, and not just in clang?

[rorth]

When building LLVM 21.1.0 rc1 on sparc64-unknown-linux-gnu, I was reminded that this is still an issue: the build is broken due to the flang failures. This is a regression from LLVM 20 and must be fixed before the LLVM 21 release.

[rorth]

I suppose a proper fix would involve enabling VIS unconditionally throughout LLVM when targeting those OSes, and not just in clang?

No idea. Maybe this belongs into clang/lib/Driver/ToolChains/Arch/Sparc.cpp instead?

[koachan]

I suppose a proper fix would involve enabling VIS unconditionally throughout LLVM when targeting those OSes, and not just in clang?

No idea. Maybe this belongs into clang/lib/Driver/ToolChains/Arch/Sparc.cpp instead?

Thanks! Moving the addition to Arch/Sparc.cpp seems to help with the errors.
Created a PR here: #149652