[BOLT] Fix incorrect basic block output addresses #70000
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Summary: Some optimization passes may duplicate basic blocks and assign the same input offset to a number of different blocks in a function. This is done e.g. to correctly map debugging ranges for duplicated code. However, duplicate input offsets present a problem when we use AddressMap to generate new addresses for basic blocks. The output address is calculated based on the input offset and will be the same for blocks with identical offsets. The result is potentially incorrect debug info and BAT records. To address the issue, we have to eliminate the dependency on input offsets while generating output addresses for a basic block. Each block has a unique label, hence we extend AddressMap to include address lookup based on MCSymbol and use the new functionality to update block addresses.
maksfb
requested review from
mtvec,
rafaelauler,
aaupov,
ayermolo and
spupyrev
mtvec
approved these changes
Oct 24, 2023
|
Thanks for quickly addressing the issue and congrats with 70000th PR :) |
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Some optimization passes may duplicate basic blocks and assign the same input offset to a number of different blocks in a function. This is done e.g. to correctly map debugging ranges for duplicated code.
However, duplicate input offsets present a problem when we use AddressMap to generate new addresses for basic blocks. The output address is calculated based on the input offset and will be the same for blocks with identical offsets. The result is potentially incorrect debug info and BAT records.
To address the issue, we have to eliminate the dependency on input offsets while generating output addresses for a basic block. Each block has a unique label, hence we extend AddressMap to include address lookup based on MCSymbol and use the new functionality to update block addresses.