[PATCH] D86621: [clang][Sparc] Default to -mcpu=v9 for SparcV8 on Solaris

Wed Aug 26 07:03:08 PDT 2020

ro created this revision.
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As reported in Bug 42535, `clang` doesn't inline atomic ops on 32-bit Sparc, unlike `gcc` on
Solaris.  In a 1-stage build with `gcc`, only two testcases are affected (currently `XFAIL`ed), while in a 2-stage build more than 100 tests `FAIL` due to this issue.

The reason for this `gcc`/`clang` difference is that `gcc` on 32-bitSolaris/SPARC defaults to `-mpcu=v9` where atomic ops are supported, unlike with `clang`'s default of `-mcpu=v8`.  This patch changes `clang` to use `-mcpu=v9` on 32-bit Solaris/SPARC, too.

Doing so uncovered two bugs:

`clang -m32 -mcpu=v9` chokes with any Solaris system headers included:

  /usr/include/sys/isa_defs.h:461:2: error: "Both _ILP32 and _LP64 are defined"
  #error "Both _ILP32 and _LP64 are defined"

While `clang` currently defines `__sparcv9` in a 32-bit `-mcpu=v9` compilation, neither `gcc` nor Studio `cc` do.  In fact, the Studio 12.6 `cc(1)` man page clearly states:

            These predefinitions are valid in all modes:
  [...]
               __sparcv8 (SPARC)
               __sparcv9 (SPARC -m64)

At the same time, the patch defines `__GCC_HAVE_SYNC_COMPARE_AND_SWAP_[1248]` for a 32-bit Sparc compilation with any V9 cpu. I've also changed `MaxAtomicInlineWidth` for V9, matching what `gcc` does and the Oracle Developer Studio 12.6: C User's Guide documents (Ch. 3, Support for Atomic Types, 3.1 Size and Alignment of Atomic C Types).

The two testcases that had been `XFAIL`ed for Bug 42535 are un-`XFAIL`ed again.  However, one of those and another testcase now `FAIL` due to Bug 42493 and are thus `XFAIL`ed.

Tested on `sparcv9-sun-solaris2.11` and `amd64-pc-solaris2.11`.

While the fix proper is trivial: just two lines in `lib/Driver/ToolChains/CommonArgs.cpp`, finding the right place has been nightmarishly difficult: I'd have expected handling of a Solaris/SPARC CPU default in either of Solaris or SPARC specific files, but not deeply hidden in common code.  I've come across issues like this over and over again: configuration information in LLVM is spread all over the place, difficult to find or just to know that it exists.

Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D86621

Files:
  clang/lib/Basic/Targets/Sparc.cpp
  clang/lib/Basic/Targets/Sparc.h
  clang/lib/Driver/ToolChains/CommonArgs.cpp
  clang/test/Preprocessor/predefined-arch-macros.c
  compiler-rt/test/profile/Posix/instrprof-gcov-parallel.test
  compiler-rt/test/ubsan/TestCases/Float/cast-overflow.cpp
  compiler-rt/test/ubsan/TestCases/Misc/log-path_test.cpp

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