Fix for avr-rust issue 129 #9
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…nvention endianness as it does not always match the overall endianness. When an argument is too large to be legalised by the architecture and is split for the ABI, we may need flexibility how we order the resulting parameters. (alternative approach recommended by Eli Friedman)
carlos4242
changed the title
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Just pushed a unit test that detects the issue. Also the problem with return values is part of a more general regression, caused by some work in rust-lang#92, also tracked in rust-lang#130 and fixed by PR #10. |
- more test cleanup - name change
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@dylanmckay no pressure intended, but the "easiest" way to get these PRs from this repo into the new llvm-project repo would be to merge them into upstream LLVM and then we can cherry-pick them 😉 |
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I'll stop being an intermittent maintainer someday ;) This is looking really nice, I'm gonna do something with it tonight, I promise!! |
dylanmckay
approved these changes
May 16, 2019
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Raised https://reviews.llvm.org/D62003 for upstreaming. |
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Cool. Let me know if I should do anything else at all? |
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The bug is related to parameter ordering and endianness. (See avr-rust rust-lang#129.)
When a large type can't be legalised, it's broken into smaller types, those are passed as parameters in order based on the endianness of the platform, which is wrong in the case of AVR (at least) because of the way those parameters are then reversed into a semi-big-endian order for the AVR GCC ABI.
The problem is the legalising is in shared code, without any existing platform specific hooks that seemed appropriate, so I added an overridable function into the TypeLoweringInfo, overridden appropriately on the AVR platform to correct the issue on AVR.
Open to comments/suggestions, also...
i) this is not yet a complete fix because the return values are suffering a similar issue too
ii) the unit test is not complete, it doesn't yet test anything