Thinlink provides an opportunity to propagate function attributes across modules, enabling additional propagation opportunities.
This change propagates (currently default off, turn on with disable-thinlto-funcattrs=1) noRecurse and noUnwind based off of function summaries of the prevailing functions in bottom-up call-graph order. Testing on clang self-build:
- There's a 35-40% increase in noUnwind functions due to the additional propagation opportunities.
- Throughput is measured at 10-15% increase in thinlink time which itself is 1.5% of E2E link time.
Implementation-wise this adds the following summary function attributes:
- noUnwind: function is noUnwind
- mayThrow: function contains a non-call instruction that Instruction::mayThrow returns true on (e.g. windows SEH instructions)
- hasUnknownCall: function contains calls that don't make it into the summary call-graph thus should not be propagated from (e.g. indirect for now, could add no-opt functions as well)
Clang self-build passes and 2nd stage build passes check-all
ninja check-all with newly added tests passing