don't empty the vec in evaluate_goal_steps

[WaffleLapkin]

No description provided.

[WaffleLapkin]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 940ed37 (940ed3712bf2ac6ce1b5e54c09127373aaf85517)
Base parent: 8e15021 (8e150217bafcaaaa0c45bf685c55fd56cec48598)

[rust-timer]

Finished benchmarking commit (940ed37): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

This perf run didn't have relevant results for this metric.

Max RSS (memory usage)

This perf run didn't have relevant results for this metric.

Cycles

Results (primary 0.4%, secondary 2.4%)

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

	mean	range	count
Regressions ❌ (primary)	1.5%	[1.3%, 1.7%]	2
Regressions ❌ (secondary)	2.4%	[2.3%, 2.5%]	2
Improvements ✅ (primary)	-1.8%	[-1.8%, -1.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[-1.8%, 1.7%]	3

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 481.812s -> 482.089s (0.06%)
Artifact size: 390.71 MiB -> 391.22 MiB (0.13%)

[lcnr]

ur only doing this in the trait solver, not in fulfill 😅 the fulfill loop is significantly hotter and with potentially more elements '^^

[rust-log-analyzer]

The job test-aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

   |                 ^^^^^^^^   ------------ type must be known at this point
   |
help: consider giving `kept_end` an explicit type, where the type for type parameter `U` is specified
   |
66 |             let kept_end: NonNull<U> = slice.cast();
   |                         ++++++++++++

error[E0133]: call to unsafe function `std::ptr::copy` is unsafe and requires unsafe block
   --> compiler/rustc_next_trait_solver/src/vec_extractor.rs:123:9
    |
123 |         ptr::copy(self.rest.as_slice().as_ptr().cast(), self.kept_end.as_ptr(), rest);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ call to unsafe function
    |
    = note: consult the function's documentation for information on how to avoid undefined behavior

error[E0133]: call to unsafe function `Vec::<T, A>::set_len` is unsafe and requires unsafe block