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[cmake] Don't build with -O3 -fPIC on Solaris/sparcv9
Tests on Solaris/sparcv9 currently show about 250 failures when building
with gcc, most of them like the following:
FAIL: LLVM-Unit :: Support/./SupportTests/TaskQueueTest.UnOrderedFutures (4269 of 67884)
******************** TEST 'LLVM-Unit :: Support/./SupportTests/TaskQueueTest.UnOrderedFutures' FAILED ********************
Note: Google Test filter = TaskQueueTest.UnOrderedFutures
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from TaskQueueTest
[ RUN ] TaskQueueTest.UnOrderedFutures
0 SupportTests 0x0000000100753b20 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 32
1 SupportTests 0x0000000100752974 llvm::sys::RunSignalHandlers() + 68
2 SupportTests 0x0000000100752b18 SignalHandler(int) + 372
3 libc.so.1 0xffffffff7eedc800 __sighndlr + 12
4 libc.so.1 0xffffffff7eecf23c call_user_handler + 852
5 libc.so.1 0xffffffff7eecf594 sigacthandler + 84
6 SupportTests 0x00000001006f8cb8 std::thread::_State_impl<std::thread::_Invoker<std::tuple<llvm::ThreadPool::ThreadPool(llvm::ThreadPoolStrategy)::'lambda'()> > >::_M_run() + 512
7 libstdc++.so.6.0.28 0xfffffffc628117cc execute_native_thread_routine + 16
8 libc.so.1 0xffffffff7eedc6a0 _lwp_start + 0
Since it's effectively impossible to debug such a `SEGV` in a `Release`
build, I tried a `Debug` build instead, only to find that the failures had
gone away.
Further investigation revealed that most of the issue centers around
`llvm/lib/Support/ThreadPool.cpp`. That file is built with `-O3 -fPIC` in
a `Release` build. The failure vanishes if
- compiling without `-fPIC`
- compiling with `-O -fPIC`
- linking with GNU `ld` instead of Solaris `ld`
It has meanwhile been determined that `gcc` doesn't correctly heed some TLS
code sequences. To make things worse, Solaris `ld` doesn't properly
validate its assumptions against the input, generating wrong code.
`gld` like `gcc` is more liberal here and correctly deals with the code it
gets fed from `gcc`.
There's PR target/96607: GCC feeds SPARC/Solaris linker with unrecognized
TLS sequences <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96607> now.
An attempt to build with `-DLLVM_ENABLE_PIC=Off` initially failed since
neither `libRemarks.so` (D85626 <https://reviews.llvm.org/D85626>) nor
`LLVMPolly.so` (D85627 <https://reviews.llvm.org/D85627>) heed that option.
Even with that fixed, a few codegen failures remain.
Next I tried to build just `ThreadPool.cpp` with `-O -fPIC`. While that
fixed the vast majority of the failures, 16 `LLVM :: CodeGen/X86` failures
remained.
Given that that solution was both incomplete and fragile, I went for
building the whole tree with `-O -fPIC` for `Release` and `RelWithDebInfo`
builds.
As detailed in Bug 47304, 2-stage builds also show large numbers of
failures when building with `-O3` or `-O2`, which are likewise worked
around by building with `-O` until they are sufficiently analyzed and
fixed.
This way, all failures relative to a `Debug` build go away.
Tested on `sparcv9-sun-solaris2.11`.
Differential Revision: https://reviews.llvm.org/D85630