Group locals by written type in binary writer#8568
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We have logic to group locals by type in the binary writer to take advantage of the run-length encoding of locals. But that logic previously grouped locals by their IR types, rather than the types that would actually be written to the binary. These can differ in when the IR uses more precise types than are allowed to be written given the enabled feature set. For example, the IR might use exact types but have to write inexact types because custom descriptors are not enabled. In such cases, it is possible that different groups of locals would be written with the same type, which is suboptimal. Fix the problem by grouping locals by their written types given the enabled features. Fixes #7934.
kripken
approved these changes
Apr 2, 2026
tlively
commented
Apr 2, 2026
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We have logic to group locals by type in the binary writer to take advantage of the run-length encoding of locals. But that logic previously grouped locals by their IR types, rather than the types that would actually be written to the binary. These can differ in when the IR uses more precise types than are allowed to be written given the enabled feature set. For example, the IR might use exact types but have to write inexact types because custom descriptors are not enabled. In such cases, it is possible that different groups of locals would be written with the same type, which is suboptimal. Fix the problem by grouping locals by their written types given the enabled features.
Fixes #7934.