Add a small speed up to PathDecanonicalized#2718
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elliotgoodrich wants to merge 1 commit intoninja-build:masterfrom
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Add a small speed up to PathDecanonicalized#2718elliotgoodrich wants to merge 1 commit intoninja-build:masterfrom
PathDecanonicalized#2718elliotgoodrich wants to merge 1 commit intoninja-build:masterfrom
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digit-google
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Jan 25, 2026
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Thanks. great PR. @jhasse please take a look
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elliotgoodrich
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Feb 8, 2026
src/graph.cc
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| c = static_cast<char*>(memchr(c, '/', end - c)); | ||
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| // If `memchr` returns null then there are too many bits in `slash_bits`, | ||
| // which happens when we pass `~0` in `build.cc` instead of calculating it. |
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Lines 997 to 1001 in cc60300
slash_bits is calculated correctly here.
Avoid a mandatory allocation in `PathDecanonicalized` by taking an output
`std::string*` to append to. Improve its performance by swapping
`strchr` with `std::string::find`, which can take advantage of knowing
the length of the string.
We can also return as soon as we run out of forwardslashes that need to be
turned into backslashes, instead of iterating through all
forwardslashes. If backslashes are the common path separator in ninja
build files on Windows, it may be worthwhile canonicalizing paths into
backslashes-only, which would now allow us to skip the loop entirely in
`PathDecanonicalized` in the case of paths with no forwardslashes.
Rename this function to `AppendPathDecanonicalized` to reflect its new
functionality.
Running `manifest_parser_perftest.exe` on Windows gives initial timings
of:
min 549ms max 613ms avg 573.1ms
and timings after this change of:
min 534ms max 597ms avg 559.9ms
which is a 2-3% improvement.
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Avoid a mandatory allocation in
PathDecanonicalizedby taking an outputstd::string*to append to. Improve its performance by swappingstrchrwithstd::string::find, which can take advantage of knowing the length of the string.We can also return as soon as we run out of forwardslashes that need to be turned into backslashes, instead of iterating through all forwardslashes.
If backslashes are the common path separator in ninja build files on Windows, it may be worthwhile canonicalizing paths into backslashes-only, which would now allow us to skip the loop entirely in
PathDecanonicalizedin the case of paths with no forwardslashes.Rename this function to
AppendPathDecanonicalizedto reflect its new functionality.Running
manifest_parser_perftest.exeon Windows gives initial timings of:and timings after this change of:
which is a 2-3% improvement.