riccibruno added a comment. In https://reviews.llvm.org/D52268#1241033, @rjmccall wrote:
> `LinkageComputer` isn't actually persisted anywhere, right? And there's > maybe one computer active at once? So this compression is theoretically > saving one pointer of stack space but forcing a bunch of bit-manipulation > every time these fields are accessed. It is not persisted but this saves one pointer per entry in the map. Another factor is that hashing a pair involves hashing each component and then combining the result, which is comparatively much more expansive than just hashing a `PointerIntPair`, which involves only a shift and a xor. The field storing the `LVComputationKind` is never directly read but only used to differentiate various kinds of computations in the map. I went back and instrumented the lookup function `LinkageComputer::lookup` with `rdtsc`, and (with all the usual caveats about microbenchmarks and `rdtsc`) I get that this cuts the number of ticks spent inside `lookup` from about 8e6 to 3.5e6. Now of course taking a step back this represent only milliseconds and is firmly in the category of "way to small to bother", but now we might as well do it. Repository: rC Clang https://reviews.llvm.org/D52268 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
