Use poison instead of undef

[nikic]

In cases where it is legal, we should prefer poison values over undef values.

This replaces undef with poison for aggregate construction and for uninhabited types. There are more places where we can likely use poison, but I wanted to stay conservative to start with.

In particular the aggregate case is important for newer LLVM versions, which are not able to handle an undef base value during early optimization due to poison-propagation concerns.

r? @cuviper

[rustbot]

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo

[cuviper]

@bors r+ rollup=never

[bors]

📌 Commit 3033182 has been approved by cuviper

It is now in the queue for this repository.

[bors]

⌛ Testing commit 3033182 with merge 4260ed21b1bc5a071a06b541c1ed363c62ab9a61...

[bors]

💔 Test failed - checks-actions

[Noratrieb]

looks spurious
@bors retry

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

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

[bors]

⌛ Testing commit 3033182 with merge 14d4992647c7efd8d722c21bd6af3ff113939252...

[rust-log-analyzer]

The job armhf-gnu failed! Check out the build log: (web) (plain)

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

---- [ui] tests/ui/nll/issue-24535-allow-mutable-borrow-in-match-guard.rs stdout ----

error: test run failed!
status: exit status: 101
command: RUST_TEST_THREADS="16" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/remote-test-client" "run" "0" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/nll/issue-24535-allow-mutable-borrow-in-match-guard/a"
uploaded "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/nll/issue-24535-allow-mutable-borrow-in-match-guard/a", waiting for result
------------------------------------------
--- stderr -------------------------------
thread 'main' panicked at 'client.read_exact(&mut header) failed with Connection reset by peer (os error 104)', src/tools/remote-test-client/src/main.rs:310:9

[bors]

💔 Test failed - checks-actions

[tmiasko]

@bors retry spurious (?) error in a remote test client

[bors]

⌛ Testing commit 3033182 with merge 54d9f6a85c06d4426ec028246b6ee661eb588d7f...

[bors]

💔 Test failed - checks-actions

[nikic]

@bors retry

[ehuss]

@bors p=100

Trying to see if incident is resolved.

[bors]

⌛ Testing commit 3033182 with merge 64a937066e507a143f2935d909cebf13e58a2cf8...

[bors]

💔 Test failed - checks-actions

[nikic]

@bors retry

[bors]

⌛ Testing commit 3033182 with merge 31d74fb...

[bors]

☀️ Test successful - checks-actions
Approved by: cuviper
Pushing 31d74fb to master...

[rust-timer]

Finished benchmarking commit (31d74fb): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	2
All ❌✅ (primary)	-	-	0

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.

	mean	range	count
Regressions ❌ (primary)	3.5%	[3.3%, 3.7%]	2
Regressions ❌ (secondary)	1.6%	[1.1%, 2.1%]	2
Improvements ✅ (primary)	-2.8%	[-2.8%, -2.8%]	1
Improvements ✅ (secondary)	-0.9%	[-1.5%, -0.6%]	5
All ❌✅ (primary)	1.4%	[-2.8%, 3.7%]	3

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.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.4%	[0.4%, 0.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.5%	[-0.5%, -0.5%]	1
All ❌✅ (primary)	-	-	0