Introduce CompileMonoItem DepNode

[bjorn3]

This is likely required for allowing efficient hot code swap support in cg_clif's jit mode. My prototype currently requires re-compiling all functions, which is both slow and uses a lot of memory as there is not support for freeing the memory used by replaced functions yet.

cc https://github.com/bjorn3/rustc_codegen_cranelift/issues/1087

[rust-highfive]

r? @petrochenkov

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[cjgillot]

Can you expand how you plan to use this DepNode? Why isn't a query not sufficient?

[bjorn3]

This is similar to CompileCodegenUnit. A query has a return value. In this case it is only done for the side-effect of compiling the mono item to a cranelift_jit::JITModule stored in a static. By using a dep node directly, I can do tcx.try_mark_green and simply do nothing if it is green or use tcx.dep_graph.with_task if it is red to run it. If it was a query, the query would always run if it isn't added to the list of queries whose result can be stored on the disk. Adding it to this list would reduce performance a bit as it is unnecessary extra work. In addition the return value of a query must be serializable, so I can't switch to some way that avoids this global static in the future but instead for example returns a Cranelift Function directly as Function doesn't implement rustc_serialize::Encodable.

[petrochenkov]

r? @wesleywiser or @davidtwco maybe

[wesleywiser]

@bors r+

[bors]

📌 Commit 21f13af has been approved by wesleywiser

[bors]

⌛ Testing commit 21f13af with merge 77ab14be6a948c8c34ff011e12caafb6a6a631d3...

[rust-log-analyzer]

The job dist-x86_64-apple failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

      Memory: 14 GB
      Boot ROM Version: VMW71.00V.13989454.B64.1906190538
      Apple ROM Info: [MS_VM_CERT/SHA1/27d66596a61c48dd3dc7216fd715126e33f59ae7]Welcome to the Virtual Machine
      SMC Version (system): 2.8f0
      Serial Number (system): VM1SsKmQg2JZ

hw.ncpu: 3
hw.byteorder: 1234
hw.memsize: 15032385536
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error: Connection to server timed out
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make[2]: *** [lib/Core/CMakeFiles/lldCore.dir/DefinedAtom.cpp.o] Error 2
make[2]: *** Waiting for unfinished jobs....
make[2]: *** [lib/Core/CMakeFiles/lldCore.dir/Error.cpp.o] Error 2
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[  9%] Building CXX object Common/CMakeFiles/lldCommon.dir/DWARF.cpp.o
clang-10: warning: argument unused during compilation: '-static-libstdc++' [-Wunused-command-line-argument]
clang-10: warning: argument unused during compilation: '-static-libstdc++' [-Wunused-command-line-argument]
clang-10: warning: argument unused during compilation: '-static-libstdc++' [-Wunused-command-line-argument]
make[1]: *** [Common/CMakeFiles/lldCommon.dir/all] Error 2
make: *** [all] Error 2
command did not execute successfully, got: exit code: 2


build script failed, must exit now', /Users/runner/.cargo/registry/src/github.heygears.com-1ecc6299db9ec823/cmake-0.1.44/src/lib.rs:885:5
 finished in 37.086 seconds
failed to run: /Users/runner/work/rust/rust/build/bootstrap/debug/bootstrap dist
Build completed unsuccessfully in 0:49:28

[bors]

💔 Test failed - checks-actions

[bjorn3]

Seems to be spurious.

@bors retry

[bors]

⌛ Testing commit 21f13af with merge 9d9c2c9...