Add 0..=isize::MAX range metadata to size loads from vtables

[erikdesjardins]

This is the (much belated) size counterpart to #91569.

Inspired by https://rust-lang.zulipchat.com/#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/Range.20metadata.20for.20.60size_of_val.60.20and.20other.20isize.3A.3AMAX.20limits. This could help optimize layout computations based on the size of a dyn trait. Though, admittedly, adding this to vtables wouldn't be as beneficial as adding it to slice len, which is used much more often.

Miri detects this UB already:

rust/compiler/rustc_const_eval/src/interpret/traits.rs

Lines 119 to 121 in b7cc991

	if size >= self.tcx.data_layout.obj_size_bound() {
	throw_ub!(InvalidVtableSize);
	}

(In fact Miri goes further, assuming a 48-bit address space on 64-bit platforms, but I don't think we can assume that in an optimization.)

[rustbot]

r? @petrochenkov

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[nikic]

@bors try @rust-timer queue

[bors]

⌛ Trying commit a99e97a with merge 1e9be934e289bcfe6465db23c6e5cdbd94078d7c...

[bors]

☀️ Try build successful - checks-actions
Build commit: 1e9be934e289bcfe6465db23c6e5cdbd94078d7c (1e9be934e289bcfe6465db23c6e5cdbd94078d7c)

[rust-timer]

Finished benchmarking commit (1e9be934e289bcfe6465db23c6e5cdbd94078d7c): comparison URL.

Overall result: no relevant changes - no action needed

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-perf -perf-regression

Instruction count

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

Max RSS (memory usage)

Results

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)	1.0%	[1.0%, 1.0%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.0%	[-1.0%, -1.0%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results

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)	1.0%	[0.9%, 1.2%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.0%	[0.9%, 1.2%]	3

[petrochenkov]

r? @nikic

[nikic]

@bors r+

[bors]

📌 Commit e01d944 has been approved by nikic

It is now in the queue for this repository.

[bors]

⌛ Testing commit e01d944 with merge 2b094b1...

[bors]

☀️ Test successful - checks-actions
Approved by: nikic
Pushing 2b094b1 to master...

[rust-timer]

Finished benchmarking commit (2b094b1): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.1%	[-1.1%, -1.1%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

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)	1.8%	[1.2%, 2.9%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	3
All ❌✅ (primary)	-	-	0

Cycles

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