Support embedding LLVM bitcode on AIX

[bzEq]

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r? @WaffleLapkin

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[WaffleLapkin]

r? compiler

[b-naber]

r? @nagisa

[nagisa]

Could you please reference some documentation on the section names AIX expects? IPA in .ipa appears to stand for inter-procedural-analysis. Is whatever stored there otherwise some sort of bytecode?

I’m particularly curious what happens if you try to link together some system library with an .ipa section with a rust library containing an .ipa section. Does that work correctly?

[bzEq]

Could you please reference some documentation on the section names AIX expects?

No, there isn't currently. We haven't support -fembed-bitcode in clang for XCOFF yet. See https://github.com/llvm/llvm-project/blob/267708f9d5150c5153e92e913c021918b790ac4f/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp#L5102.

The purpose of this PR currently is to workaround linking issue we have encountered during bootstrap, since the linker doesn't recognize the inline assembly generated by

rust/compiler/rustc_codegen_llvm/src/back/write.rs

Line 903 in 696aaad

} else {

.

IPA in .ipa appears to stand for inter-procedural-analysis. Is whatever stored there otherwise some sort of bytecode?

We are planning to support LTO on AIX, and this might be the name of the section to store LLVM bitcode.

I’m particularly curious what happens if you try to link together some system library with an .ipa section with a rust library containing an .ipa section.

AIX linker will ignore .ipa sections and they won't appear in the final object file if no symbol references this section.

[bzEq]

@rustbot ready

[nagisa]

Ah, sorry for missing this!

AIX linker will ignore .ipa sections and they won't appear in the final object file if no symbol references this section.

Awesome, this is the behaviour that resolves any worries I might have had about keeping this section.

@bors r+

[bors]

📌 Commit 7b79cb1 has been approved by nagisa

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7b79cb1 with merge 56d507d...

[bors]

☀️ Test successful - checks-actions
Approved by: nagisa
Pushing 56d507d to master...

[rust-timer]

Finished benchmarking commit (56d507d): 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.

	mean	range	count
Regressions ❌ (primary)	0.9%	[0.5%, 1.3%]	2
Regressions ❌ (secondary)	2.7%	[2.7%, 2.7%]	1
Improvements ✅ (primary)	-0.8%	[-1.5%, -0.4%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-1.5%, 1.3%]	6

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)	2.8%	[2.8%, 2.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 659.918s -> 660.386s (0.07%)