Remove current code for embedding command-line args in PDB

[Zalathar]

The compiler currently has code that will obtain a list of quoted command-line arguments, and pass it through to TargetMachine creation, so that the command-line args can be embedded in PDB output.

This PR removes that code, due to subtle concerns that might not have been apparent when it was originally added.

---

Those concerns include:

• The entire command-line quoting process is repeated every time a target-machine-factory is created. In incremental builds this typically occurs 500+ times, instead of happening only once. The repeated quoting constitutes a large chunk of instructions executed in the large-workspace benchmark.
  • See (EXPERIMENT) Perf experiments for target-machine command-line quoting #146804 (comment) for an example of the perf consequences of skipping all that work.
  • This overhead occurs even when building for targets or configurations that don't emit PDB output.
• Command-line arguments are obtained in a way that completely bypasses the query system, which is a problem for the integrity of incremental compilation.
  • Fixing this alone is likely to inhibit incremental rebuilds for most or all CGUs, even in builds that don't emit PDB output.
• Command-line arguments and the executable path are obtained in a way that completely bypasses the compiler's path-remapping system, which is a reproducibility hazard.
  • LF_BUILDINFO introduces non-determinism to Windows rlib builds #128842

---

Relevant PRs:

• Add CL and CMD into to pdb debug info #113492
• rustc_llvm: adapt to flattened CLI args in LLVM #130446
• rustc_llvm: Fix flattened CLI args #131805
• cg_llvm: Move target machine command-line quoting from C++ to Rust #146700
• Compute quoted args for debuginfo at most once per session #146973

Zulip thread:

• https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/Some.20PDB.20info.20bypasses.20the.20query.20system.20and.20path.20remapping/with/541432211

---

According to #96475, one of the big motivations for embedding the command-line arguments was to enable tools like Live++. It appears that Live++ doesn't actually support Rust yet, so it's possible that there aren't any existing workflows for this removal to break.

In the future, there could be a case for reintroducing some or all of this functionality, guarded behind an opt-in flag so that it doesn't cause problems for other users. But as it stands, the current implementation puts a disproportionate burden on other users and on compiler maintainers.

[rustbot]

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

[rustbot]

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[Zalathar]

@bors try @rust-timer queue

[Zalathar]

Looks flaky. Let’s try again.

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: e4d7ba7 (e4d7ba78e779e732d68b8f16c4348091513822d2, parent: 7cfd7d328b14b936c7ffede92cacebe8557c6388)

[rust-timer]

Finished benchmarking commit (e4d7ba7): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-0.5%, -0.2%]	8
Improvements ✅ (secondary)	-3.7%	[-20.6%, -0.7%]	17
All ❌✅ (primary)	-0.3%	[-0.5%, -0.2%]	8

Max RSS (memory usage)

Results (primary 4.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	4.1%	[4.1%, 4.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.1%	[4.1%, 4.1%]	1

Cycles

Results (secondary -2.8%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.4%	[2.0%, 2.7%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.2%	[-7.2%, -2.1%]	11
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 469.935s -> 470.607s (0.14%)
Artifact size: 388.04 MiB -> 388.06 MiB (0.01%)

[petrochenkov]

@rfcbot merge

[rust-rfcbot]

Team member @petrochenkov has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Mark-Simulacrum
• @Noratrieb
• @SparrowLii
• @cjgillot
• @compiler-errors
• @davidtwco
• @estebank
• @jieyouxu
• @matthewjasper
• @nagisa
• @oli-obk
• @petrochenkov
• @spastorino
• @wesleywiser

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