Parallelize LLVM image generation

doc/src/devdocs/sysimg.md

@@ -8,6 +8,9 @@ as many platforms as possible, so as to give vastly improved startup times.  On
 not ship with a precompiled system image file, one can be generated from the source files shipped
 in Julia's `DATAROOTDIR/julia/base` folder.
 
+Julia will by default generate its system image on half of the available system threads. This
+may be controlled by the [`JULIA_IMAGE_THREADS`](@ref env-image-threads) environment variable.
+
 This operation is useful for multiple reasons.  A user may:
 
   * Build a precompiled shared library system image on a platform that did not ship with one, thereby

doc/src/manual/environment-variables.md

@@ -277,7 +277,7 @@ To use Visual Studio Code on Windows, set `$JULIA_EDITOR` to `code.cmd`.
 
 ## Parallelization
 
-### `JULIA_CPU_THREADS`
+### [`JULIA_CPU_THREADS`](@id env-cpu-threads)
 
 Overrides the global variable [`Base.Sys.CPU_THREADS`](@ref), the number of
 logical CPU cores available.
@@ -316,6 +316,19 @@ then spinning threads never sleep. Otherwise, `$JULIA_THREAD_SLEEP_THRESHOLD` is
 interpreted as an unsigned 64-bit integer (`uint64_t`) and gives, in
 nanoseconds, the amount of time after which spinning threads should sleep.
 
+### [`JULIA_IMAGE_THREADS`](@id env-image-threads)
+
+An unsigned 32-bit integer that sets the number of threads used by image
+compilation in this Julia process. The value of this variable may be
+ignored if the module is a small module. If left unspecified, the smaller
+of the value of [`JULIA_CPU_THREADS`](@ref env-cpu-threads) or half the
+number of logical CPU cores is used in its place.
+
+### `JULIA_IMAGE_TIMINGS`
+
+A boolean value that determines if detailed timing information is printed during
+during image compilation. Defaults to 0.
+
 ### `JULIA_EXCLUSIVE`
 
 If set to anything besides `0`, then Julia's thread policy is consistent with

src/Makefile

@@ -287,7 +287,7 @@ $(BUILDDIR)/julia_flisp.boot: $(addprefix $(SRCDIR)/,jlfrontend.scm flisp/aliase
 
 # additional dependency links
 $(BUILDDIR)/codegen-stubs.o $(BUILDDIR)/codegen-stubs.dbg.obj: $(SRCDIR)/intrinsics.h
-$(BUILDDIR)/aotcompile.o $(BUILDDIR)/aotcompile.dbg.obj: $(SRCDIR)/jitlayers.h $(SRCDIR)/llvm-codegen-shared.h
+$(BUILDDIR)/aotcompile.o $(BUILDDIR)/aotcompile.dbg.obj: $(SRCDIR)/jitlayers.h $(SRCDIR)/llvm-codegen-shared.h $(SRCDIR)/processor.h
 $(BUILDDIR)/ast.o $(BUILDDIR)/ast.dbg.obj: $(BUILDDIR)/julia_flisp.boot.inc $(SRCDIR)/flisp/*.h
 $(BUILDDIR)/builtins.o $(BUILDDIR)/builtins.dbg.obj: $(SRCDIR)/iddict.c $(SRCDIR)/builtin_proto.h
 $(BUILDDIR)/codegen.o $(BUILDDIR)/codegen.dbg.obj: $(addprefix $(SRCDIR)/,\