Define _RUST_STAGEN when building rustrt. #6714
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This lets us use #ifdefs to determine which stage of the build we happen to be in, which is useful in the event we need to make changes to rustrt that are incompatible with the code generated by stage0. This should help pave the way to completing rust-lang#6575, which will likely require changes to type signatures for spawn_fn & glue_fn in rustrt.
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Oh, wow. It didn't occur to me that we only build rt in one stage. This is a bigger task than I thought. |
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I think this is probably the cleanest way to do this, since it makes the rt build like the rest of the libraries, but it is going to increase build times. We used to have a flag in the makefiles called USE_SNAPSHOT_RT (removed in e343abd) that we removed because it was no longer being used. That flag was used to make this sort of change by reusing the snapshot rt, core and/or std libraries in stage0. |
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@catamorphism What do you think of this? |
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@brson How much of an increase in build times do you think it will be? IME, the runtime doesn't take very long to build compared to the compiler and libraries. |
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@catamorphism Yeah, it shouldn't be that much, and it's parallelizable. |
As discussed with @brson on IRC: This lets us use #ifdefs to determine which stage of the build we happen to be in, which is useful in the event we need to make changes to rustrt that are incompatible with the code generated by a stage0 rustc. Example of the _RUST_STAGEN flag in action here: https://gist.github.com/thomaslee/5641890 I'm not sure what tests for this change should look like, so please advise if I need to do some work around that.
Fix typo changelog: none
As discussed with @brson on IRC:
This lets us use #ifdefs to determine which stage of the build we happen
to be in, which is useful in the event we need to make changes to rustrt
that are incompatible with the code generated by a stage0 rustc.
Example of the _RUST_STAGEN flag in action here: https://gist.github.com/thomaslee/5641890
I'm not sure what tests for this change should look like, so please advise if I need to do some work around that.