StateTransform: Only load pin field once.

[cjgillot]

The current implementation starts by transforming all instances of _1 into (*_1), and then traverses the body again to transform (*_1) into (*(_1.0)), and again for Derefer.

This PR changes the implementation to only traverse the body once. As _1.0 cannot be not modified inside the body (we just changed its type!), we have no risk of loading from the wrong pointer.

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[rustbot]

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[cjgillot]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 8a45031 (8a45031b817c65c13e267ee4f0c1aa833399b480, parent: 7a52736039856a3626eefec32d80c9df900b7afd)

[rust-timer]

Finished benchmarking commit (8a45031): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@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)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.9%	[-1.9%, -0.2%]	16
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary -5.2%)

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
Improvements ✅ (secondary)	-5.2%	[-5.2%, -5.2%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary 0.3%)

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)	1.9%	[1.5%, 2.4%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-2.9%, -2.9%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.0%, secondary -1.8%)

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)	-0.0%	[-0.1%, -0.0%]	7
Improvements ✅ (secondary)	-1.8%	[-6.0%, -0.2%]	12
All ❌✅ (primary)	-0.0%	[-0.1%, -0.0%]	7

Bootstrap: 472.232s -> 472.472s (0.05%)
Artifact size: 388.41 MiB -> 388.41 MiB (-0.00%)

[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.