Let codegen_transmute_operand just handle everything

[scottmcm]

When combined with #143720, this means rvalue_creates_operand can just return true for every Rvalue. (A future PR could consider removing it, though just letting it optimize out is fine for now.)

It's nicer anyway, IMHO, because it avoids needing the layout checks to be consistent in the two places, and thus is an overall reduction in code. Plus it's a more helpful building block when used in other places this way.

(TBH, it probably would have been better to have it this way the whole time, but I clearly didn't understand rvalue_creates_operand when I originally wrote #109843.)

[rustbot]

r? @petrochenkov

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[rustbot]

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

[scottmcm]

@bors try @rust-timer queue

[bors]

⌛ Trying commit af1b680 with merge 1790c15...

[bors]

☀️ Try build successful - checks-actions
Build commit: 1790c15 (1790c15cb9074d67a9a5edd4ea709796b02df1ff)

[rust-timer]

Finished benchmarking commit (1790c15): comparison URL.

Overall result: ❌ regressions - no action needed

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.

@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)	0.4%	[0.4%, 0.5%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary -4.0%)

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)	-4.0%	[-4.0%, -4.0%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -2.1%)

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)	-2.1%	[-2.1%, -2.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.1%	[-2.1%, -2.1%]	1

Binary size

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

Bootstrap: 464.174s -> 465.333s (0.25%)
Artifact size: 374.70 MiB -> 374.75 MiB (0.01%)