While investigating the optimizations performed by my prove CL 196679, I found out these two instances of what looks like dead code:
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j, searchIdx := s.chunkOf(ci).find(npages, 0) |
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if j < 0 { |
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// We couldn't find any space in this chunk despite the summaries telling |
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// us it should be there. There's likely a bug, so dump some state and throw. |
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sum := s.summary[len(s.summary)-1][i] |
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print("runtime: summary[", len(s.summary)-1, "][", i, "] = (", sum.start(), ", ", sum.max(), ", ", sum.end(), ")\n") |
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print("runtime: npages = ", npages, "\n") |
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throw("bad summary data") |
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} |
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j, searchIdx := s.chunkOf(i).find(npages, chunkPageIndex(s.searchAddr)) |
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if j < 0 { |
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print("runtime: max = ", max, ", npages = ", npages, "\n") |
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print("runtime: searchIdx = ", chunkPageIndex(s.searchAddr), ", s.searchAddr = ", hex(s.searchAddr), "\n") |
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throw("bad summary data") |
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} |
That branch is never taken because pallocBits.find() return an unsigned number:
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// find searches for npages contiguous free pages in pallocBits and returns |
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// the index where that run starts, as well as the index of the first free page |
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// it found in the search. searchIdx represents the first known free page and |
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// where to begin the search from. |
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// |
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// If find fails to find any free space, it returns an index of ^uint(0) and |
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// the new searchIdx should be ignored. |
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// |
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// Note that if npages == 1, the two returned values will always be identical. |
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func (b *pallocBits) find(npages uintptr, searchIdx uint) (uint, uint) { |
Given the documentation, it looks like the failure is reported as ^uint(0) so the above checks are probably wrong.
/cc @aclements @mknyszek
