In order to extract the module dependency graph from the compilation the driver just ran, define a separate semantic type to hold a result code and the graph itself.
The target was added for Unix toolchains in #901, but a later pull #1891 added
it again. Since clang only uses the last target flag that's passed in, all
customization done for the first one was unused these last 4+ years, so remove
it and change tests that look for custom strings passed by the first one.
The "wave" of a compilation job describes the number of indirections through other compile jobs the driver required to reach the decision to schedule a job. In incremental mode, it should always be the case that it takes no more than two complete waves to arrive at a fixpoint in the build. This is a natural consequence of the structure of the dependencies emitted by the Swift frontend - namely we rely on transitivity in dependency arcs.
A quick proof sketch: Suppose an arbitrary perturbation of the inputs to an incremental compilation session are made. In the first wave, dependency edges from the prior build's state (the "zeroeth wave") are loaded and the files corresponding to invalidated edges are scheduled into the first wave. Supposing the second wave is not the null set - the trivial case - there are additional arcs that were invalidated. Now suppose that there were a third wave. Take an arbitrary arc invalidated by this third wave. It must be the case that the file containing the use is not new - else it would be scheduled. Further it must be the case that its def was not invalidated by the zeroeth or first waves of compilation otherwise we would have scheduled it into the first or second waves. Finally, it must have a use that was discovered in the second wave. But in order for that use to have been included in the second wave, there must have been an invalidated arc created by the first wave. By transitivity of dependency arcs, there must therefore be a dependency arc from a definition invalidated in the first wave to our third wave job, which implies that the file would be scheduled into the second wave!
[Insert contradiction pig image here]
In order to unblock the SwiftWASM project, which relies on an
incremental build of the Swift driver that relies on the merge-modules
job always being run. The situation appears to be something like this:
1) An incremental build is run
2) Temporary swiftmodule outputs are laid down
3) merge-modules is skipped
4) modulewrap is run anyways and reads the empty temp file
We should fix this by skipping modulewrap if we can skip merge-modules.
But for now, be conservative and fall back to the status quo behavior of
always running merge-modules whenever we encounter a modulewrap job.
Plumb the logic necessary to schedule merge-modules incrementally. This means that if any inputs jobs to merge-modules run, merge-modules is run. But, if they are all skipped, merge-modules will be skipped as well.
This requires some light special-casing of the legacy driver's incremental job handling because it assumes in a few places it can always extract a swiftdeps file. This invariant will be further broken when the precompile step for bridging headers is skipped as well.
rdar://65893400
The Optional parameter here was being copied instead of being taken by
const reference. The expectation is that we call this function and
extract the data from a ModuleDepGraphNode node, but instead we were
extracting a copy which would promptly blow up.
Thanks ASAN!
A more durable form of #34218. Keep a side cache of externally-dependent
jobs for now. This ensures our pseudo-Jobs don't get prematurely
deallocated before the tracing machinery has had a chance to report the
structure of the Job graph.
rdar://70053563
The fake job is entered into the map to satisfy the tracing machinery.
When that same machinery kicks into gear to print out paths, lookups
into the dictionary will access data has gone out of scope.
For now, cut off the read. There will be another refactoring patch that
keeps these temporaries out of the Driver's data structures entirely.
rdar://70053563
An incremental build involving incremental external dependencies behaves as a hybrid between an external dependency and a normal swiftdeps-laden Swift file.
In the simplest case, we will fall back to the behavior of a plain external dependency today. That is, we will check its timestamp, then schedule all jobs that involve these external dependencies if it is out of date.
Where things get interesting is when cross-module incremental builds are enabled. In such a case, we know that a previous compiler has already emitted serialized swiftdeps information inside of a swiftmodule file. Moreover, we know that that swiftmodule file was loaded by the build of the current swift module. Finally, thanks to the previous stack of commits, we now know exactly how to extract this information from the swiftmodule file. To bring this all home, we unpack incremental dependency information from external dependencies, then integrate them into the current dependency graph - as though they were any other swiftdeps file. This neatly extends the single-module incremental logic to the multi-module case.
Treat any incremental external depends like normal external depends. This will eventually become the fallback behavior for cross-module incremental builds.
With this option enabled, the dependency scanner gathers all import statements in source files of the main module (non-transitive) and outputs a list of imported modules.
This will be used by build systems and the swift-driver as a way to avoid redundant re-scanning in incremental contexts.
