make PlaceholderConst not store the type of the const

[BoxyUwU]

Currently the Placeholder variant on ConstKind is 28 bytes when with this PR its 8 bytes, i am not sure this is really useful at all rn since Unevaluated and Value variants are huge still but eventually it should be possible to get both down to 16 bytes 🤔. Mostly opening this to see if this change has any perf impact when done before it can make ConstKind/ConstS smaller

[rust-highfive]

r? @estebank

(rust-highfive has picked a reviewer for you, use r? to override)

[compiler-errors]

i was always confused why this ty was stored twice in constkind...

[BoxyUwU]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit 49d001c with merge c2f4c0cd4fd72ff97cdb105e3b869619de400589...

[bors]

☀️ Try build successful - checks-actions
Build commit: c2f4c0cd4fd72ff97cdb105e3b869619de400589 (c2f4c0cd4fd72ff97cdb105e3b869619de400589)

[rust-timer]

Queued c2f4c0cd4fd72ff97cdb105e3b869619de400589 with parent c9e134e, future comparison URL.

[rust-timer]

Finished benchmarking commit (c2f4c0cd4fd72ff97cdb105e3b869619de400589): comparison url.

Instruction count

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

Max RSS (memory usage)

Results

• Primary benchmarks: 🎉 relevant improvement found
• Secondary benchmarks: 🎉 relevant improvement found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	-2.3%	-2.3%	1
Improvements 🎉 (secondary)	-3.0%	-3.0%	1
All 😿🎉 (primary)	-2.3%	-2.3%	1

Cycles

Results

• Primary benchmarks: 😿 relevant regression found
• Secondary benchmarks: no relevant changes found

	mean1	max	count2
Regressions 😿 (primary)	3.0%	3.0%	1
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	3.0%	3.0%	1

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

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

Footnotes

1. the arithmetic mean of the percent change ↩ ↩²

2. number of relevant changes ↩ ↩²

[compiler-errors]

@BoxyUwU: r=me unless you want someone else's review specifically! This is totally worth landing just for the code simplification, even if there's no perf impact.

[BoxyUwU]

@bors r=compiler-errors

[bors]

📌 Commit 49d001c has been approved by compiler-errors

It is now in the queue for this repository.

[bors]

⌛ Testing commit 49d001c with merge 06f4950...

[bors]

☀️ Test successful - checks-actions
Approved by: compiler-errors
Pushing 06f4950 to master...

[rust-timer]

Finished benchmarking commit (06f4950): comparison url.

Instruction count

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

Max RSS (memory usage)

Results

• Primary benchmarks: 🎉 relevant improvement found
• Secondary benchmarks: no relevant changes found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	-3.8%	-3.8%	1
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	-3.8%	-3.8%	1

Cycles

Results

• Primary benchmarks: no relevant changes found
• Secondary benchmarks: 😿 relevant regression found

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	6.2%	6.2%	1
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	N/A	N/A	0

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩²

2. number of relevant changes ↩ ↩²