Get rid of mir::Const::from_ty_const

[compiler-errors]

This function is strange, because it turns valtrees into mir::Const::Value, but the rest of the const variants stay as type system consts.

All of the callsites except for one in instsimplify (array length simplification of ptr_metadata call) just go through the valtree arm of the function, so it's easier to just create a mir::Const directly for those.

For the instsimplify case, if we have a type system const we should keep having a type system const, rather than turning it into a mir::Const::Value; it doesn't really matter in practice, though, bc usize has no padding, but it feels more principled.

[rustbot]

r? @oli-obk

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[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in exhaustiveness checking

cc @Nadrieril

[oli-obk]

@bors r+ rollup=never

May be perf sensitive

[bors]

📌 Commit e9a5660 has been approved by oli-obk

It is now in the queue for this repository.

[scottmcm]

For the instsimplify case, if we have a type system const we should keep having a type system const, rather than turning it into a mir::Const::Value; it doesn't really matter in practice, though, bc usize has no padding, but it feels more principled.

...and you'll be deleting this shortly (in #135748) anyway :)

[jieyouxu]

@bors p=5 (threading between rollups)

[bors]

⌛ Testing commit e9a5660 with merge d9b4598...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing d9b4598 to master...

[rust-timer]

Finished benchmarking commit (d9b4598): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (secondary 3.2%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.2%	[3.2%, 3.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary 6.6%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	6.6%	[6.6%, 6.6%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.0%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.0%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.0%]	1

Bootstrap: 771.892s -> 773.047s (0.15%)
Artifact size: 325.83 MiB -> 325.89 MiB (0.02%)