Try to shrink Alignment-related MIR in Layout

[scottmcm]

Noticed all this in https://rust.godbolt.org/z/55Tx65v4e:

        _22 = (_11.0: std::ptr::alignment::AlignmentEnum);
        _23 = discriminant(_22);
        _24 = Ge(_23, const 1_u64);
        _25 = Le(_23, const 9223372036854775808_u64);
        _26 = BitAnd(move _24, move _25);
        assume(move _26);
        _20 = _23 as usize (IntToInt);

So let's see if a non-as here works better.

[rustbot]

r? @joboet

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[scottmcm]

@bors try @rust-timer queue

[bors]

⌛ Trying commit ddcdc0e with merge 688a0c0...

[bors]

☀️ Try build successful - checks-actions
Build commit: 688a0c0 (688a0c061d888ae4c35fa5be1840a076d22f6644)

[rust-timer]

Finished benchmarking commit (688a0c0): comparison URL.

Overall result: ❌✅ regressions and improvements - 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.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +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)	0.4%	[0.4%, 0.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.7%, -0.3%]	5
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.3%	[-0.7%, 0.4%]	6

Max RSS (memory usage)

Results (primary 0.4%, secondary 2.6%)

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)	3.2%	[1.6%, 5.1%]	5
Regressions ❌ (secondary)	2.6%	[2.0%, 3.1%]	2
Improvements ✅ (primary)	-4.3%	[-5.3%, -2.7%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[-5.3%, 5.1%]	8

Cycles

Results (primary -1.0%)

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

Binary size

Results (primary 0.0%, secondary 0.3%)

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)	0.2%	[0.1%, 0.6%]	13
Regressions ❌ (secondary)	0.3%	[0.3%, 0.3%]	1
Improvements ✅ (primary)	-0.1%	[-0.6%, -0.0%]	23
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[-0.6%, 0.6%]	36

Bootstrap: 762.097s -> 760.688s (-0.18%)
Artifact size: 339.28 MiB -> 339.26 MiB (-0.00%)

[erikdesjardins]

Note that after #128371, we should be able to remove the assume entirely.

[joboet]

If #128371 does indeed fix this, I'd prefer that, so let's wait for that PR to be merged first.

[erikdesjardins]

#128371 enables the assumes to be removed, but doesn't do so.

I just opened #129027 which removes the assumes and should obviate the need for this change.