Rollup of 6 pull requests
Successful merges:
- #125263 (rust-lld: fallback to rustc's sysroot if there's no path to the linker in the target sysroot)
- #125345 (rustc_codegen_llvm: add support for writing summary bitcode)
- #125362 (Actually use TAIT instead of emulating it)
- #125412 (Don't suggest adding the unexpected cfgs to the build-script it-self)
- #125445 (Migrate `run-make/rustdoc-with-short-out-dir-option` to `rmake.rs`)
- #125452 (Cleanup check-cfg handling in core and std)
r? `@ghost`
`@rustbot` modify labels: rollup
If we don't do this, some versions of LLVM (at least 17, experimentally)
will double-emit some error messages, which is how I noticed this. Given
that it seems to be costing some extra work, let's only request the
summary bitcode production if we'll actually bother writing it down,
otherwise skip it.
Typical uses of ThinLTO don't have any use for this as a standalone
file, but distributed ThinLTO uses this to make the linker phase more
efficient. With clang you'd do something like `clang -flto=thin
-fthin-link-bitcode=foo.indexing.o -c foo.c` and then get both foo.o
(full of bitcode) and foo.indexing.o (just the summary or index part of
the bitcode). That's then usable by a two-stage linking process that's
more friendly to distributed build systems like bazel, which is why I'm
working on this area.
I talked some to @teresajohnson about naming in this area, as things
seem to be a little confused between various blog posts and build
systems. "bitcode index" and "bitcode summary" tend to be a little too
ambiguous, and she tends to use "thin link bitcode" and "minimized
bitcode" (which matches the descriptions in LLVM). Since the clang
option is thin-link-bitcode, I went with that to try and not add a new
spelling in the world.
Per @dtolnay, you can work around the lack of this by using `lld
--thinlto-index-only` to do the indexing on regular .o files of
bitcode, but that is a bit wasteful on actions when we already have all
the information in rustc and could just write out the matching minimized
bitcode. I didn't test that at all in our infrastructure, because by the
time I learned that I already had this patch largely written.
Stop allowing `rustc::potential_query_instability` on all of
`rustc_codegen_llvm` and instead allow it on a case-by-case basis. In
this case, both instances are safe to allow.
If the TargetMachine is disposed after the Context is disposed, it can
lead to use after frees in some cases.
I've observed this happening occasionally on code compiled for
aarch64-pc-windows-msvc using `-Zstack-protector=strong` but other users
have reported AVs from host aarch64-pc-windows-msvc compilers as well.
Upstream change
llvm/llvm-project@6b539f5eb8 changed
`isSectionBitcode` works and it now only respects `.llvm.lto` sections
instead of also `.llvmbc`, which it says was never intended to be used
for LTO. We instead load sections by name, and sniff for raw bitcode by
hand.
r? @nikic
@rustbot label: +llvm-main
This reverts #46722, commit e0ab5d5feb.
Since #111167, commit 10b69dde3f, we are
generating DWARF subprograms in a way that is meant to be more compatible
with LLVM's expectations, so hopefully we don't need this workaround
rewriting CUs anymore.
Currently, LLVM profiling runtime counter relocation cannot be
used by rust during LTO because symbols are being internalized
before all symbol information is known.
This mode makes LLVM emit a __llvm_profile_counter_bias symbol
which is referenced by the profiling initialization, which itself
is pulled in by the rust driver here [1].
It is enabled with -Cllvm-args=-runtime-counter-relocation for
platforms which are opt-in to this mode like Linux. On these
platforms there will be no link error, rather just surprising
behavior for a user which request runtime counter relocation.
The profiling runtime will not see that symbol go on as if it
were never there. On Fuchsia, the profiling runtime must have
this symbol which will cause a hard link error.
As an aside, I don't have enough context as to why rust's LTO
model is how it is. AFAICT, the internalize pass is only safe
to run at link time when all symbol information is actually
known, this being an example as to why. I think special casing
this symbol as a known one that LLVM can emit which should not
have it's visbility de-escalated should be fine given how
seldom this pattern of defining an undefined symbol to get
initilization code pulled in is. From a quick grep,
__llvm_profile_runtime is the only symbol that rustc does this
for.
[1] 0265a3e93b/compiler/rustc_codegen_ssa/src/back/linker.rs (L598)
The compiler currently has `-Ztime` and `-Ztime-passes`. I've used
`-Ztime-passes` for years but only recently learned about `-Ztime`.
What's the difference? Let's look at the `-Zhelp` output:
```
-Z time=val -- measure time of rustc processes (default: no)
-Z time-passes=val -- measure time of each rustc pass (default: no)
```
The `-Ztime-passes` description is clear, but the `-Ztime` one is less so.
Sounds like it measures the time for the entire process?
No. The real difference is that `-Ztime-passes` prints out info about passes,
and `-Ztime` does the same, but only for a subset of those passes. More
specifically, there is a distinction in the profiling code between a "verbose
generic activity" and an "extra verbose generic activity". `-Ztime-passes`
prints both kinds, while `-Ztime` only prints the first one. (It took me
a close reading of the source code to determine this difference.)
In practice this distinction has low value. Perhaps in the past the "extra
verbose" output was more voluminous, but now that we only print stats for a
pass if it exceeds 5ms or alters the RSS, `-Ztime-passes` is less spammy. Also,
a lot of the "extra verbose" cases are for individual lint passes, and you need
to also use `-Zno-interleave-lints` to see those anyway.
Therefore, this commit removes `-Ztime` and the associated machinery. One thing
to note is that the existing "extra verbose" activities all have an extra
string argument, so the commit adds the ability to accept an extra argument to
the "verbose" activities.
Allow to disable thinLTO buffer to support lto-embed-bitcode lld feature
Hello
This change is to fix issue (https://github.com/rust-lang/rust/issues/84395) in which passing "-lto-embed-bitcode=optimized" to lld when linking rust code via linker-plugin-lto doesn't produce the expected result.
Instead of emitting a single unified module into a llvmbc section of the linked elf, it emits multiple submodules.
This is caused because rustc emits the BC modules after running llvm `createWriteThinLTOBitcodePass` pass.
Which in turn triggers a thinLTO linkage and causes the said issue.
This patch allows via compiler flag (-Cemit-thin-lto=<bool>) to select between running `createWriteThinLTOBitcodePass` and `createBitcodeWriterPass`.
Note this pattern of selecting between those 2 passes is common inside of LLVM code.
The default is to match the old behavior.
Revert "Work around invalid DWARF bugs for fat LTO"
Since September, the toolchain has not been generating reliable DWARF
information for static variables when LTO is on. This has affected
projects in the embedded space where the use of LTO is typical. In our
case, it has kept us from bumping past the 2021-09-22 nightly toolchain
lest our debugger break. This has been a pretty dramatic regression for
people using debuggers and static variables. See #90357 for more info
and a repro case.
This commit is a mechanical revert of
d5de680e20 from PR #89041, which caused
the issue. (Note on that PR that the commit's author has requested it be
reverted.)
I have locally verified that this fixes#90357 by restoring the
functionality of both the repro case I posted on that bug, and debugger
behavior on real programs. There do not appear to be test cases for this
in the toolchain; if I've missed them, point me at 'em and I'll update
them.
Adding the option to control from rustc CLI
if the resulted ".o" bitcode module files are with
thinLTO info or regular LTO info.
Allows using "-lto-embed-bitcode=optimized" during linkage
correctly.
Signed-off-by: Ziv Dunkelman <ziv.dunkelman@nextsilicon.com>
To apply the optimization the `Virtual Function Elim` module flag has to
be set. To apply this optimization post-link the `LTOPostLink` module
flag has to be set.
