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Stuart Pernsteiner
cf672850df
Refactor the code in `llvm::back` that invokes LLVM optimization and codegen passes so that it can be called from worker threads. (Previously, it used `&Session` extensively, and `Session` is not `Share`.) The new code can handle multiple compilation units, by compiling each unit to `crate.0.o`, `crate.1.o`, etc., and linking together all the `crate.N.o` files into a single `crate.o` using `ld -r`. The later linking steps can then be run unchanged. The new code preserves the behavior of `--emit`/`-o` when building a single compilation unit. With multiple compilation units, the `--emit=asm/ir/bc` options produce multiple files, so combinations like `--emit=ir -o foo.ll` will not actually produce `foo.ll` (they instead produce several `foo.N.ll` files). The new code supports `-Z lto` only when using a single compilation unit. Compiling with multiple compilation units and `-Z lto` will produce an error. (I can't think of any good reason to do such a thing.) Linking with `-Z lto` against a library that was built as multiple compilation units will also fail, because the rlib does not contain a `crate.bytecode.deflate` file. This could be supported in the future by linking together the `crate.N.bc` files produced when compiling the library into a single `crate.bc`, or by making the LTO code support multiple `crate.N.bytecode.deflate` files.