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Rollup merge of #113723 - khei4:khei4/llvm-stats, r=oli-obk,nikic

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Resurrect: rustc_llvm: Add a -Z `print-codegen-stats` option to expose LLVM statistics.

This resurrects PR https://github.com/rust-lang/rust/pull/104000, which has sat idle for a while. And I want to see the effect of stack-move optimizations on LLVM (like https://reviews.llvm.org/D153453) :).

I have applied the changes requested by `@oli-obk` and `@nagisa`  https://github.com/rust-lang/rust/pull/104000#discussion_r1014625377 and https://github.com/rust-lang/rust/pull/104000#discussion_r1014642482 in the latest commits.

r? `@oli-obk`

-----

LLVM has a neat [statistics](https://llvm.org/docs/ProgrammersManual.html#the-statistic-class-stats-option) feature that tracks how often optimizations kick in. It's very handy for optimization work. Since we expose the LLVM pass timings, I thought it made sense to expose the LLVM statistics too.

-----
(Edit: fix broken link
(Edit2: fix segmentation fault and use malloc

If `rustc` is built with
```toml
[llvm]
assertions = true
```
Then you can see like
```
rustc +stage1 -Z print-codegen-stats -C opt-level=3  tmp.rs
===-------------------------------------------------------------------------===
                          ... Statistics Collected ...
===-------------------------------------------------------------------------===
         3 aa                           - Number of MayAlias results
       193 aa                           - Number of MustAlias results
       531 aa                           - Number of NoAlias results
...
```

And the current default build emits only
```
$ rustc +stage1 -Z print-codegen-stats -C opt-level=3  tmp.rs
===-------------------------------------------------------------------------===
                          ... Statistics Collected ...
===-------------------------------------------------------------------------===
$
```
This might be better to emit the message to tell assertion flag necessity, but now I can't find how to do that...
This commit is contained in:
Matthias Krüger 2023-07-21 06:52:27 +02:00 • committed by GitHub
commit 2734b5ada9
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10 changed files with 69 additions and 5 deletions
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3
compiler/rustc_session/src/options.rs
View file

@ -1668,6 +1668,9 @@ options! {
"use a more precise version of drop elaboration for matches on enums (default: yes). \
This results in better codegen, but has caused miscompilations on some tier 2 platforms. \
See #77382 and #74551."),
#[rustc_lint_opt_deny_field_access("use `Session::print_codegen_stats` instead of this field")]
print_codegen_stats: bool = (false, parse_bool, [UNTRACKED],
"print codegen statistics (default: no)"),
print_fuel: Option<String> = (None, parse_opt_string, [TRACKED],
"make rustc print the total optimization fuel used by a crate"),
print_llvm_passes: bool = (false, parse_bool, [UNTRACKED],

4
compiler/rustc_session/src/session.rs
View file

@ -1057,6 +1057,10 @@ impl Session {
self.opts.unstable_opts.verbose
}
pub fn print_llvm_stats(&self) -> bool {
self.opts.unstable_opts.print_codegen_stats
}
pub fn verify_llvm_ir(&self) -> bool {
self.opts.unstable_opts.verify_llvm_ir || option_env!("RUSTC_VERIFY_LLVM_IR").is_some()
}