try to reduce impact of scalar size checks

[RalfJung]

Investigating the perf regression in #161238.

[RalfJung]

@bors try
@rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 5e1a5a6 (5e1a5a6052b5d6d684b94bb5c2842e53fa58a153)
Base parent: 16a623a (16a623ad672a92409b5c04beb303583c6cf72a7e)

[rust-timer]

Finished benchmarking commit (5e1a5a6): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

@bors rollup=never rustc-perf
@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%	[-0.4%, -0.2%]	6
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.3%	[-0.4%, -0.2%]	6

Max RSS (memory usage)

Results (primary 2.1%, secondary 2.1%)

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

	mean	range	count
Regressions ❌ (primary)	2.1%	[0.7%, 3.5%]	2
Regressions ❌ (secondary)	6.4%	[6.4%, 6.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.2%	[-2.2%, -2.2%]	1
All ❌✅ (primary)	2.1%	[0.7%, 3.5%]	2

Cycles

Results (primary 2.4%, secondary 6.9%)

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

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.2%, 2.6%]	2
Regressions ❌ (secondary)	6.9%	[6.9%, 6.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.4%	[2.2%, 2.6%]	2

Binary size

Results (primary 0.1%, secondary 0.1%)

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

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.2%]	116
Regressions ❌ (secondary)	0.1%	[0.0%, 0.2%]	121
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.2%]	116

Bootstrap: 457.604s -> 457.186s (-0.09%)
Artifact size: 398.89 MiB -> 398.99 MiB (0.03%)

[RalfJung]

Looks like the right direction, but not quite enough. So I guess it's code size here, where previously we just constructed a little struct and now we invoke the panic machinery.

[RalfJung]

@bors try
@rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: d8dc741 (d8dc741a46ffa8d3eb34711760f4c5154fecbe5c)
Base parent: b662191 (b66219142c937562f2ff8e083be2a2b25b20199e)

[rust-timer]

Finished benchmarking commit (d8dc741): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

@bors rollup=never rustc-perf
@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)	-0.4%	[-0.5%, -0.4%]	6
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.4%	[-0.5%, -0.4%]	6

Max RSS (memory usage)

Results (primary 2.9%, secondary -1.3%)

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

	mean	range	count
Regressions ❌ (primary)	2.9%	[2.5%, 3.3%]	2
Regressions ❌ (secondary)	2.9%	[2.9%, 2.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.5%	[-5.5%, -5.5%]	1
All ❌✅ (primary)	2.9%	[2.5%, 3.3%]	2

Cycles

Results (primary -2.6%, secondary -1.9%)

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)	1.6%	[1.6%, 1.6%]	1
Improvements ✅ (primary)	-2.6%	[-3.0%, -2.1%]	2
Improvements ✅ (secondary)	-3.1%	[-3.6%, -2.7%]	3
All ❌✅ (primary)	-2.6%	[-3.0%, -2.1%]	2

Binary size

Results (primary -0.1%, secondary -0.1%)

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)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.0%]	93
Improvements ✅ (secondary)	-0.1%	[-0.2%, -0.0%]	66
All ❌✅ (primary)	-0.1%	[-0.2%, -0.0%]	93

Bootstrap: 470.067s -> 467.991s (-0.44%)
Artifact size: 400.02 MiB -> 400.02 MiB (0.00%)

[RalfJung]

That's at least reasonably close to the red numbers in the original PR I think.
r? @petrochenkov
since you reviewed the previous PR

[rustbot]

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri, @oli-obk, @lcnr

[rustbot]

r? @jackh726

rustbot has assigned @jackh726.
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