Clean up codegen_niche_literal #1486
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danielsn
approved these changes
Aug 11, 2022
| FieldsShape::Arbitrary { offsets, .. } => offsets[0], | ||
| _ => unreachable!("niche encoding must have arbitrary fields"), | ||
| }; | ||
| let niche_offset = layout.fields.offset(*tag_field); |
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Nice instead of hardcoding zero
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Description of changes:
Clean up
codegen_niche_literal: this does not require generating a separate function, similarly to #1457. I believe (and added assertions to that effect) that this code is only called when the whole type is the same size as the discriminant type and the offset of the discriminant is 0. Hence we can simply transmute the given scalar to the result type.Resolved issues:
Resolves #1485
Call-outs
This adds a byte extract instruction. I vaguely remember CBMC struggling with this sometimes. But it seems better than casting to a pointer, adding an offset and dereferencing, which is what we used to do.
Testing:
How is this change tested? Existing regression tests
Is this a refactor change? yes
Checklist
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.