Upgrade to LLVM's master branch (LLVM 7) #51966

alexcrichton · 2018-07-01T16:55:39Z

Current status

~~Blocked on a performance regression. The performance regression has an upstream LLVM issue and has also been bisected to an LLVM revision.~~

Ready to merge!

This commit upgrades the main LLVM submodule to LLVM's current master branch.
The LLD submodule is updated in tandem as well as compiler-builtins.

Along the way support was also added for LLVM 7's new features. This primarily
includes the support for custom section concatenation natively in LLD so we now
add wasm custom sections in LLVM IR rather than having custom support in rustc
itself for doing so.

Some other miscellaneous changes are:

We now pass --gc-sections to wasm-ld
The optimization level is now passed to wasm-ld
A --stack-first option is passed to LLD to have stack overflow always cause
a trap instead of corrupting static data
The wasm target for LLVM switched to wasm32-unknown-unknown.
The syntax for aligned pointers has changed in LLVM IR and tests are updated
to reflect this.
~~The thumbv6m-none-eabi target is disabled due to an LLVM bug~~

Nowadays we've been mostly only upgrading whenever there's a major release of
LLVM but enough changes have been happening on the wasm target that there's been
growing motivation for quite some time now to upgrade out version of LLD. To
upgrade LLD, however, we need to upgrade LLVM to avoid needing to build yet
another version of LLVM on the builders.

The revision of LLVM in use here is arbitrarily chosen. We will likely need to
continue to update it over time if and when we discover bugs. Once LLVM 7 is
fully released we can switch to that channel as well.

cc #50543

rust-highfive · 2018-07-01T16:55:42Z

r? @varkor

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

rust-highfive · 2018-07-01T16:55:43Z

Warning

These commits modify submodules.

alexcrichton · 2018-07-01T16:56:09Z

cc @fitzgen for the LLD update
cc @japaric ~~for the proposed removal of thumbv6m-none-eabi~~

varkor · 2018-07-02T00:52:28Z

src/librustc_codegen_llvm/back/linker.rs

+            OptLevel::Less => "-O1",
+            OptLevel::Default => "-O2",
+            OptLevel::Aggressive => "-O3",
+            OptLevel::Size => "-O2",


If this is intentional, it'd be helpful to have a comment here to explain why -O2 is used for the size opt levels (as opposed to -Os and -Oz).

Sure thing!

varkor · 2018-07-02T00:58:06Z

Everything looks reasonable to me, but it'd be better to have someone more familiar check over this.
r? @michaelwoerister

alexcrichton · 2018-07-02T21:43:23Z

Now that https://bugs.llvm.org/show_bug.cgi?id=37382 is fixed I've updated to bring back the thumbv6m build

alexcrichton · 2018-07-02T21:45:17Z

Oh one thing I forgot to mention in the OP as well is that there's a change to src/librustdoc/fold.rs which is a hack around either a bug in LLVM or a bug in our code generation. I was unable to reduce it down after a week or so of attempting various strategies, so I've opted to go ahead and apply the hack and see if we can find a reduced case in the wild.

alexcrichton · 2018-07-02T21:52:34Z

@bors: try

bors · 2018-07-02T21:53:39Z

⌛ Trying commit f29cd71c42d5099fd693e040f3802dc1c9548070 with merge b77640fe5342825939a1222f847c753f7b3c0968...

bors · 2018-07-11T07:20:21Z

⌛ Testing commit 42eb850 with merge ae5b629...

bors · 2018-07-11T10:00:25Z

☀️ Test successful - status-appveyor, status-travis
Approved by: michaelwoerister
Pushing ae5b629 to master...

Set opt-level = 3 the third time. This PR reverts #51165 (set -O2 to fix #50867), which reverted #50329 (set -O3), which was second attempt of #48204 (set -O3, closed due to Windows segfault that is fixed now), which reverted #42123 (set -O2 to fix spurious Windows segfaults), which reverted #41967 (set -O3). Last time we've found that setting -O3 regressed the wall time of NLL (#50329 (comment)), so we may need another perf run to confirm. I'd like to check this *after* the LLVM 7 upgrade #51966 has been merged, so marking this as <kbd>S-blocked</kbd> for now.

alexcrichton · 2018-07-11T14:08:23Z

Hm, this was a suspiciously smooth upgrade...

nnethercote · 2018-07-12T00:00:14Z

Perf regressions showed up on perf.rust-lang.org as expected:
https://perf.rust-lang.org/compare.html?start=4700e1188f66fdb4086b7593416b678b8fe935f4&end=989fa053895a27fd40896335224b619843b7e58a&stat=instructions:u

Then there was a slight improvement immediately afterward due to #51230:
https://perf.rust-lang.org/compare.html?start=989fa053895a27fd40896335224b619843b7e58a&end=66787e05242d86e0bcfa227265559330c45cdc42&stat=instructions:u

varkor · 2018-07-12T19:26:55Z

llvm-rebuild-trigger wasn't modified as part of this PR, which was an oversight. Is it worth updating in a standalone PR, to ease the transition for anyone who isn't yet up to date with master?

alexcrichton · 2018-07-12T19:29:23Z

Sure!

@alexcrichton

…excrichton Update llvm-rebuild-trigger in light of LLVM 7 upgrade Not triggering a LLVM rebuild [since the LLVM 7 upgrade](rust-lang#51966 (comment)) causes builds of rustc to fail. r? @alexcrichton

@alexcrichton

…excrichton Update llvm-rebuild-trigger in light of LLVM 7 upgrade Not triggering a LLVM rebuild [since the LLVM 7 upgrade](rust-lang#51966 (comment)) causes builds of rustc to fail. r? @alexcrichton

@alexcrichton

…excrichton Update llvm-rebuild-trigger in light of LLVM 7 upgrade Not triggering a LLVM rebuild [since the LLVM 7 upgrade](rust-lang#51966 (comment)) causes builds of rustc to fail. r? @alexcrichton

Set opt-level = 3 the third time. This PR reverts #51165 (set -O2 for fixing #50867), which reverted #50329 (set -O3), which was second attempt of #48204 (set -O3, closed due to Windows segfault that is fixed now), which reverted #42123 (set -O2 to fix spurious Windows segfaults), which reverted #41967 (set -O3). Since we have found the root cause of #50867, this optimization could be tried again. Last time we've found that setting -O3 regressed the wall time of NLL (#50329 (comment)), so we may need another perf run to confirm. I'd like to check this *after* the LLVM 7 upgrade #51966 has been merged, so marking this as <kbd>S-blocked</kbd> for now.

varkor · 2019-09-26T11:10:17Z

src/librustc/hir/check_attr.rs

@@ -57,7 +57,7 @@ struct CheckAttrVisitor<'a, 'tcx: 'a> {
 impl<'a, 'tcx> CheckAttrVisitor<'a, 'tcx> {
    /// Check any attribute.
    fn check_attributes(&self, item: &hir::Item, target: Target) {
-        if target == Target::Fn {
+        if target == Target::Fn || target == Target::Const {


@alexcrichton: what motivated this change?

Uh... well it's been over a year, so this is way out of cache. I suspect this was done to handle wasm attribute validation, but you are wondering you can remove this then seems fine to remove it.

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alexcrichton force-pushed the llvm7 branch from f440272 to 1f687f4 Compare July 1, 2018 17:05

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alexcrichton force-pushed the llvm7 branch 2 times, most recently from abbd4fc to aa667e3 Compare July 2, 2018 14:16

japaric mentioned this pull request Jul 2, 2018

Embedded WG meeting, July 2 rust-embedded/wg#110

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alexcrichton force-pushed the llvm7 branch 2 times, most recently from 1e57200 to f29cd71 Compare July 2, 2018 21:43

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bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 2, 2018

bors merged commit 42eb850 into rust-lang:master Jul 11, 2018

alexcrichton deleted the llvm7 branch July 11, 2018 14:08

glandium mentioned this pull request Jul 12, 2018

panic code is not deterministically lto'ed #52044

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varkor mentioned this pull request Jul 12, 2018

Update llvm-rebuild-trigger in light of LLVM 7 upgrade #52322

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alexcrichton mentioned this pull request Jul 13, 2018

LLVM 7.0 tracking issue #50543

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matklad mentioned this pull request Jul 14, 2018

New nightly shows mysterious changes of binary size rustwasm/team#214

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pepyakin mentioned this pull request Jul 15, 2018

Use --export-table from the latest LLD paritytech/substrate#316

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alexcrichton mentioned this pull request Jul 16, 2018

Duplicate definitions for enums in generated bindings rustwasm/wasm-bindgen#483

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sekineh mentioned this pull request Jul 18, 2018

Add CI test harness for thumb* targets. [IRR-2018-embedded] #52465

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bradjc mentioned this pull request Jul 23, 2018

RISCV Arch Support rust-embedded/wg#36

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cramertj mentioned this pull request Jul 31, 2018

Compiler segfaults when compiling the vte crate for aarch64 #52884

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japaric mentioned this pull request Aug 2, 2018

error: linker rust-lld not found #52362

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petrochenkov mentioned this pull request Aug 5, 2018

A number of debuginfo tests now fail on Windows/GNU and maybe other platforms #53098

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appaquet mentioned this pull request Feb 19, 2019

Support Apple app store bitcode #35968

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kennytm mentioned this pull request Mar 10, 2019

1.29 fails to build on a Windows networked drive #54216

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pnkfelix mentioned this pull request Jun 24, 2019

llvm lint: "Undefined behavior: Call argument type mismatches callee parameter type" with mixing debug and release #48310

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alexcrichton mentioned this pull request Aug 13, 2023

Compile time regression introduced in r322401 llvm/llvm-project#37436

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Upgrade to LLVM's master branch (LLVM 7) #51966

Upgrade to LLVM's master branch (LLVM 7) #51966

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Upgrade to LLVM's master branch (LLVM 7) #51966

Upgrade to LLVM's master branch (LLVM 7) #51966

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