Improve codegen for bitfield operations #3325
Open
+19,616
−4,707
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Replace bit-at-a-time loops in get(), set(), raw_get(), and raw_set() with byte-wise shift/mask operations. This significantly improves performance for multi-bit field access. The new implementation reads/writes bytes in chunks and uses shifts and masks to extract/insert values, rather than iterating over each bit individually. For big-endian targets, the algorithm reverses bits within bytes and the final value to maintain the same semantics as the original implementation.
jsgf
force-pushed
the
fix-bitfield-get
branch
2 times, most recently
from
9f5c6c5 to
00e5503
Compare
Add a specialized impl block for `__BindgenBitfieldUnit<[u8; N]>` with const-generic methods: `get_const`, `set_const`, `raw_get_const`, and `raw_set_const`. These methods take bit offset and width as const generic parameters, allowing the compiler to fully optimize bitfield access at compile time. Update codegen to use the new const-generic methods for generated bitfield accessors. Since all bitfield offsets and widths are known at code generation time, this enables better optimization. The original runtime-parameter methods are preserved for backwards compatibility with users who provide custom implementations via the blocklist mechanism.
jsgf
force-pushed
the
fix-bitfield-get
branch
from
00e5503 to
8496a59
Compare
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The current bit-at-a-time implementations of bitfield insertion and extraction can generate very bad code, at least for riscv. This PR does two things:
Since in general bitfields have constant offset and size, having a function with const params allows the code to be even more specialized at compile time.