Conditionally enable debug! with --cfg debug
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…a noop based on cfg(debug).
Macros can be conditionally defined because stripping occurs before macro
expansion, but, the built-in macros were only added as part of the actual
expansion process and so couldn't be stripped to have definitions conditional
on cfg flags.
debug! is defined conditionally in terms of the debug config, expanding to
nothing unless the --cfg debug flag is passed (to be precise it expands to
`if false { normal_debug!(...) }` so that they are still type checked, and
to avoid unused variable lints).
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I'll discuss this in the meeting today to make sure the team is OK with this. Thanks! |
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(This is currently broken, fixing it now.) @pcwalton ok. FWIW, I think @alexcrichton's experimentation may've indicated a bigger performance gain, so my measurements are possibly skewed by my background use. (I guess we could get a definitive answer if @cmr's bencher stopped being unroutable.) |
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My "measurements" should barely be considered that. I just ad-hocly ran |
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Doing this for all of the logging statements would be nice. Like, |
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(Not that info/warn/error are really used...) |
The entire testsuite is converted to using info! rather than debug! because some depend on the code within the debug! being trans'd.
…ectly. An alloca in an unreachable block would shortcircuit with Undef, but with type `Type`, rather than type `*Type` (i.e. a plain value, not a pointer) but it is expected to return a pointer into the stack, leading to confusion and LLVM asserts later. Similarly, attaching the range metadata to a Load in an unreachable block makes LLVM unhappy, since the Load returns Undef. Fixes rust-lang#7344.
That is, the `b` branch in `if true { a } else { b }` will not be
trans'd, and that expression will be exactly the same as `a`. This
means that, for example, macros conditionally expanding to `if false
{ .. }` (like debug!) will not waste time in LLVM (or trans).
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Jul 16, 2013
As per @pcwalton's request, `debug!(..)` is only activated when the `debug` cfg is set; that is, for `RUST_LOG=some_module=4 ./some_program` to work, it needs to be compiled with `rustc --cfg debug some_program.rs`. (Although, there is the sneaky `__debug!(..)` macro that is always active, if you *really* need it.) It functions by making `debug!` expand to `if false { __debug!(..) }` (expanding to an `if` like this is required to make sure `debug!` statements are typechecked and to avoid unused variable warnings), and adjusting trans to skip the pointless branches in `if true ...` and `if false ...`. The conditional expansion change also required moving the inject-std-macros step into a new pass, and makes it actually insert them at the top of the crate; this means that the cfg stripping traverses over the macros and so filters out the unused ones. This appears to takes an unoptimised build of `librustc` from 65s to 59s; and the full bootstrap from 18m41s to 18m26s on my computer (with general background use). `./configure --enable-debug` will enable `debug!` statements in the bootstrap build.
flip1995
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Oct 21, 2021
`unnecessary_sort_by` checks if argument implements `Ord` trait closes rust-lang#7822 changelog: [`unnecessary_sort_by`] now checks if argument implements `Ord` trait
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As per @pcwalton's request,
debug!(..)is only activated when thedebugcfg is set; that is, forRUST_LOG=some_module=4 ./some_programto work, it needs to be compiled withrustc --cfg debug some_program.rs. (Although, there is the sneaky__debug!(..)macro that is always active, if you really need it.)It functions by making
debug!expand toif false { __debug!(..) }(expanding to aniflike this is required to make suredebug!statements are typechecked and to avoid unused variable warnings), and adjusting trans to skip the pointless branches inif true ...andif false ....The conditional expansion change also required moving the inject-std-macros step into a new pass, and makes it actually insert them at the top of the crate; this means that the cfg stripping traverses over the macros and so filters out the unused ones.
This appears to takes an unoptimised build of
librustcfrom 65s to 59s; and the full bootstrap from 18m41s to 18m26s on my computer (with general background use)../configure --enable-debugwill enabledebug!statements in the bootstrap build.