Use struct tail rather than metadata projection to compute coercion fast path

[compiler-errors]

cc #136127 (comment)

r? @ghost

[compiler-errors]

@bors try @rust-timer queue

[bors]

⌛ Trying commit b4cee9b with merge fbd9a21...

[bors]

☀️ Try build successful - checks-actions
Build commit: fbd9a21 (fbd9a21cdbc244602badb8908a529ff58579acfc)

[rust-timer]

Finished benchmarking commit (fbd9a21): comparison URL.

Overall result: ✅ improvements - 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 is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.5%	[-0.8%, -0.2%]	23
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 2.0%)

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)	2.0%	[2.0%, 2.0%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.0%	[2.0%, 2.0%]	1

Cycles

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

Binary size

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

Bootstrap: 770.102s -> 768.521s (-0.21%)
Artifact size: 361.98 MiB -> 361.98 MiB (-0.00%)

[compiler-errors]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 8ff333e with merge 19ae219...

[bors]

☀️ Try build successful - checks-actions
Build commit: 19ae219 (19ae2193b48a0d96abbd3d3ba745b99a240a14e0)

[rust-timer]

Finished benchmarking commit (19ae219): comparison URL.

Overall result: ✅ improvements - 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 is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.9%	[-3.3%, -0.2%]	92
Improvements ✅ (secondary)	-3.7%	[-11.5%, -0.5%]	68
All ❌✅ (primary)	-0.9%	[-3.3%, -0.2%]	92

Max RSS (memory usage)

Results (primary 0.9%, secondary -4.4%)

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)	3.0%	[3.0%, 3.0%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-4.4%	[-6.7%, -1.9%]	7
All ❌✅ (primary)	0.9%	[-1.1%, 3.0%]	2

Cycles

Results (primary -1.9%, secondary -5.8%)

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)	4.1%	[4.0%, 4.2%]	2
Improvements ✅ (primary)	-1.9%	[-4.0%, -1.0%]	18
Improvements ✅ (secondary)	-6.4%	[-12.0%, -1.9%]	31
All ❌✅ (primary)	-1.9%	[-4.0%, -1.0%]	18

Binary size

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

Bootstrap: 779.823s -> 777.929s (-0.24%)
Artifact size: 365.18 MiB -> 365.13 MiB (-0.01%)

[compiler-errors]

i have to rework how we emit diagnostics here i guess

[WaffleLapkin]

@rustbot author
based on the last comment and draft status

[compiler-errors]

not sure who the relabeling is for given this isn't assigned to anyone 🤔

[WaffleLapkin]

I'm eepy and thought I'm assigned to this (was confused by reviewer suggestions). Oops /_=

[compiler-errors]

anyways this pr was a failed experiment and is superseded by a more involved change in #138438