compiler/rustc_codegen_ssa/src/mir/place.rs: Remove LLVM bug workaround

[mikebenfield]

This memset was inserted as a workaround to Rust issue #34427, which was
an LLVM bug that apparently no longer manifests.

[rust-highfive]

r? @TaKO8Ki

(rust-highfive has picked a reviewer for you, use r? to override)

[RalfJung]

Cc @nikic

[mikebenfield]

FWIW, I've verified that on an aarch64-unknown-linux-gnu machine, both ./x.py test --stage 1 and ./x.py test --stage 2 pass with this commit.

[cuviper]

Would you be able to try a 32-bit ARM toolchain as well?
(AArch64 and ARM are separate targets in LLVM.)

[mikebenfield]

Unfortunately I won't have access to an arm (not aarch64) machine in the immediate future. Worst case scenario it'll be tested on an arm machine before merge right?

[cuviper]

We don't have a 32-bit arm machine in CI, but we do test arm-android, cross-compiled and executed in qemu.

[RalfJung]

This is effectively a revert of #36496, so also Cc @pnkfelix

[cuviper]

I found a Fedora community machine to try armv7-unknown-linux-gnueabihf, and it looks good there as well.

[nikic]

@bors r+ rollup=never

[bors]

📌 Commit 12a9914 has been approved by nikic

It is now in the queue for this repository.

[bors]

⌛ Testing commit 12a9914 with merge 4f9898a...

[bors]

☀️ Test successful - checks-actions
Approved by: nikic
Pushing 4f9898a to master...

[rust-timer]

Finished benchmarking commit (4f9898a): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results

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.

	mean1	range	count2
Regressions ❌ (primary)	5.3%	[5.3%, 5.3%]	1
Regressions ❌ (secondary)	2.6%	[2.1%, 3.1%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.8%	[-6.8%, -6.8%]	1
All ❌✅ (primary)	5.3%	[5.3%, 5.3%]	1

Cycles

Results

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.

	mean1	range	count2
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-2.4%, -2.4%]	1
All ❌✅ (primary)	-	-	0

Footnotes

1. the arithmetic mean of the percent change ↩ ↩²

2. number of relevant changes ↩ ↩²