rustc: Upgrade to LLVM 6

[alexcrichton]

The following submodules have been updated for a new version of LLVM:

• src/llvm
• src/libcompiler_builtins - transitively contains compiler-rt
• src/dlmalloc

This also updates the docker container for dist-i686-freebsd as the old 16.04
container is no longer capable of building LLVM. The
compiler-rt/compiler-builtins and dlmalloc updates are pretty routine without
much interesting happening, but the LLVM update here is of particular note.
Unlike previous updates I haven't cherry-picked all existing patches we had on
top of our LLVM branch as we have a huge amount and have at this
point forgotten what most of them are for. Instead I started from the current
release_60 branch in LLVM and only applied patches that were necessary to get
our tests working and building.

The current set of custom rustc-specific patches included in this LLVM update are:

• rust-lang/llvm@1187443 - this is how we actually implement
  cfg(target_feature) for now and continues to not be upstreamed. While a
  hazard for SIMD stabilization this commit is otherwise keeping the status
  quo of a small rustc-specific feature.
• rust-lang/llvm@013f2ec - this is a rustc-specific optimization that we haven't
  upstreamed, notably teaching LLVM about our allocation-related routines (which
  aren't malloc/free). Once we stabilize the global allocator routines we will
  likely want to upstream this patch, but for now it seems reasonable to keep it
  on our fork.
• rust-lang/llvm@a65bbfd - I found this necessary to fix compilation of LLVM in
  our 32-bit linux container. I'm not really sure why it's necessary but my
  guess is that it's because of the absolutely ancient glibc that we're using.
  In any case it's only updating pieces we're not actually using in LLVM so I'm
  hoping it'll turn out alright. This doesn't seem like something we'll want to
  upstream.c
• rust-lang/llvm@77ab1f0 - this is what's actually enabling LLVM to build in our
  i686-freebsd container, I'm not really sure what's going on but we for sure
  probably don't want to upstream this and otherwise it seems not too bad for
  now at least.
• rust-lang/llvm@9eb9267 - we currently suffer on MSVC from an upstream bug
  which although diagnosed to a particular revision isn't currently fixed
  upstream (and the bug itself doesn't seem too active). This commit is a
  partial revert of the suspected cause of this regression (found via a
  bisection). I'm sort of hoping that this eventually gets fixed upstream with a
  similar fix (which we can replace in our branch), but for now I'm also hoping
  it's a relatively harmless change to have.

After applying these patches (plus one backport which should be backported
upstream) I believe we should have all tests working on all
platforms in our current test suite. I'm like 99% sure that we'll need some more
backports as issues are reported for LLVM 6 when this propagates through
nightlies, but that's sort of just par for the course nowadays!

In any case though some extra scrutiny of the patches here would definitely be
welcome, along with scrutiny of the "missing patches" like a change to pass
manager order, another change to pass manager
order, some compile fixes for
sparc, and some fixes for
solaris.

---

The update to LLVM 6 is desirable for a number of reasons, notably:

• This'll allow us to keep up with the upstream wasm backend, picking up new
  features as they start landing.
• Upstream LLVM has fixed a number of SIMD-related compilation errors,
  especially around AVX-512 and such.
• There's a few assorted known bugs which are fixed in LLVM 5 and aren't fixed
  in the LLVM 4 branch we're using.
• Overall it's not a great idea to stagnate with our codegen backend!

This update is mostly powered by #47730 which is allowing us to update LLVM
independent of the version of LLVM that Emscripten is locked to. This means
that when compiling code for Emscripten we'll still be using the old LLVM 4
backend, but when compiling code for any other target we'll be using the new
LLVM 6 target. Once Emscripten updates we may no longer need this distinction,
but we're not sure when that will happen!

Closes#43370
Closes#43418
Closes#47015
Closes#47683
Closesrust-lang/stdarch#157
Closes rust-lang-nursery/rust-wasm#3

[rust-highfive]

r? @nikomatsakis

(rust_highfive has picked a reviewer for you, use r? to override)

[alexcrichton]

Note that this is currently based on #47730 which I'll rebase out once that lands. Also @rust-lang/infra could this get a perf run and a crater run? (to hopefully head of anything massive!)

@bors: try

cc @rust-lang/compiler

[bors]

⌛ Trying commit d9031ae with merge 38bd381...

[bors]

☀️ Test successful - status-travis
State: approved= try=True

[alexcrichton]

Perf comparison shows that nothing is too bad!

[est31]

Up to 13.5% improvement... wow.

[nikomatsakis]

@bors r+

Let's do it.

[bors]

📌 Commit 586488c has been approved by nikomatsakis

[cuviper]

rust-lang/llvm@1187443 - this is how we actually implement
cfg(target_feature) for now and continues to not be upstreamed. While a
hazard for SIMD stabilization this commit is otherwise keeping the status
quo of a small rustc-specific feature.

Maybe update run-pass/sse2 to // min-llvm-version 6.0? But really that needs a rustllvm flag.

Apart from that, testing on this branch also looks good with external LLVM 5.

[mattico]

I did some investigation on the FreeBSD issue. FreeBSD 10 uses Clang 3.0. Clang didn't support std::atomic until 3.3. I think that's all the issue is. FreeBSD 10 is only supported until Oct 31 of this year, so it should be safe to update that soon enough.

[alexcrichton]

@cuviper ah yes that test should definitely have a // no-system-llvm flag. Otherwise though this is an existing issue, I just wanted to highlight it again :)

@mattico ok cool, thanks!

[kennytm]

@bors p=1

[bors]

⌛ Testing commit 586488c with merge 22d405f...

[bors]

💔 Test failed - status-appveyor

[kennytm]

😕

Assuming spurious first.

@bors retry #33434

Could not compile rustc_errors with error code 3221225477 (0xc0000005)

[01:40:22] Building stage1 compiler artifacts (x86_64-pc-windows-msvc -> x86_64-pc-windows-msvc)
[01:40:22] Compiling graphviz v0.0.0 (file:///C:/projects/rust/src/libgraphviz)
<snip>
[01:41:43] Compiling rustc_errors v0.0.0 (file:///C:/projects/rust/src/librustc_errors)
[01:41:49] error: Could not compile `rustc_errors`.
[01:41:49] [01:41:49] Caused by:
[01:41:49] process didn't exit successfully: `C:\projects\rust\build\bootstrap/debug/rustc --crate-name rustc_errors librustc_errors\lib.rs --color always --error-format json --crate-type dylib --emit=dep-info,link -C prefer-dynamic -C opt-level=2 -C metadata=65687244e9f663b1 -C extra-filename=-65687244e9f663b1 --out-dir C:\projects\rust\build\x86_64-pc-windows-msvc\stage1-rustc\x86_64-pc-windows-msvc\release\deps --target x86_64-pc-windows-msvc -L dependency=C:\projects\rust\build\x86_64-pc-windows-msvc\stage1-rustc\x86_64-pc-windows-msvc\release\deps -L dependency=C:\projects\rust\build\x86_64-pc-windows-msvc\stage1-rustc\release\deps --extern rustc_data_structures=C:\projects\rust\build\x86_64-pc-windows-msvc\stage1-rustc\x86_64-pc-windows-msvc\release\deps\rustc_data_structures-fe1c5452c3c89758.dll --extern serialize=C:\projects\rust\build\x86_64-pc-windows-msvc\stage1-rustc\x86_64-pc-windows-msvc\release\deps\serialize-e9133ab5aa0e0076.dll --extern serialize=C:\projects\rust\build\x86_64-pc-windows-msvc\stage1-rustc\x86_64-pc-windows-msvc\release\deps\libserialize-e9133ab5aa0e0076.rlib --extern unicode_width=C:\projects\rust\build\x86_64-pc-windows-msvc\stage1-rustc\x86_64-pc-windows-msvc\release\deps\libunicode_width-850dabec54650530.rlib --extern syntax_pos=C:\projects\rust\build\x86_64-pc-windows-msvc\stage1-rustc\x86_64-pc-windows-msvc\release\deps\syntax_pos-f4ba1a45fc002844.dll` (exit code: 3221225477)
[01:41:49] thread 'main' panicked at 'command did not execute successfully: "C:\\projects\\rust\\build\\x86_64-pc-windows-msvc\\stage0/bin\\cargo.exe" "build" "--target" "x86_64-pc-windows-msvc" "-j" "2" "--release" "--locked" "--color" "always" "--features" "" "--manifest-path" "C:\\projects\\rust\\src/rustc/Cargo.toml" "--message-format" "json"
[01:41:49] expected success, got: exit code: 101', bootstrap\compile.rs:1062:9
[01:41:49] note: Run with `RUST_BACKTRACE=1` for a backtrace.
[01:41:49] failed to run: C:\projects\rust\build\bootstrap\debug\bootstrap dist

[alexcrichton]

@bors: r-

nah I saw that in development and thought it was spurious, at this point I sort of doubt it is...

[Zoxc]

I see access violations all the time when building on Windows using master, rebuilding makes it go away, so this error might be spurious.

[bors]

⌛ Testing commit 6b7b6b6 with merge 39abcc0...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: nikomatsakis
Pushing 39abcc0 to master...

[kennytm]

o_O The debugging code seems harmless, but is this supposed to be get actually merged now?

[alexcrichton]

@kennytm I'm sort of just glad to have this done with, but I'll send a follow-up to clean up that code. With #47657 (comment) though it seems like it's not helping anyway...

[shepmaster]

With #47657 (comment) though it seems like it's not helping anyway...

I think you meant to refer to #48116?

[alexcrichton]

@shepmaster oh I was just linking to the failure on #47657, but yeah #48116 is in general tracking the failure.

[boozook]

Now really looking forward to the bitcode feature of LLVM7. Today - LLVM6, tomorrow - LLVM7!

[martell]

@alexcrichton
Author of https://reviews.llvm.org/D29892 here

rust-lang/llvm@9eb9267 - we currently suffer on MSVC from an upstream bug which although diagnosed to a particular revision isn't currently fixed upstream (and the bug itself doesn't seem too active). This commit is a partial revert of the suspected cause of this regression (found via a bisection). I'm sort of hoping that this eventually gets fixed upstream with a similar fix (which we can replace in our branch), but for now I'm also hoping it's a relatively harmless change to have.

https://bugs.llvm.org/show_bug.cgi?id=36096
Let's make this bug report a little more active and see if we can find the correct fix. :)

[gaming-hacker]

Not to nag but has this issue with llvm-60 been resolved on OSX/Linux and merged into master?

[shepmaster]

@gaming-hacker

Yes it has been merged. You can tell by scrolling to the top of the page and checking out the header:

If you click through to the commit, you can see which tags the commit is part of:

You can also check out the 1.25 release notes which lists this (emphasis mine):

The last few releases have been relatively minor, but Rust 1.25 contains a bunch of stuff! The first one is straightforward: we’ve upgraded to LLVM 6 from LLVM 4

[gaming-hacker]

Ah thanks, i use source tree as a gui to display the status of the commits and it shows these as unmerged, i'll report a bug to source tree.