[PATCH 1/3] Makefile: make the "sparse" target non-.PHONY

Change the "sparse" target and its *.sp dependencies to be non-.PHONY. It's now viable to run it as part of a normal compilation target, as we'll only re-generate these checks if the source *.c file has changed.

On my box with -j8 it was fast before, or around 5 seconds, now it only takes that long the first time, and the common case is <100ms, or however long it takes GNU make to stat the *.sp file and see that all the corresponding *.c files are older.

See 0bcd9ae85d7 (sparse: Fix errors due to missing target-specific variables, 2011-04-21) for the modern implementation of the sparse target being changed here.

It is critical that we use -Wsparse-error here, otherwise the error would only show up once, but we'd successfully create the empty *.sp file, and running a second time wouldn't show the error. I'm therefore not putting it into SPARSE_FLAGS or SP_EXTRA_FLAGS, it's not optional, the Makefile logic won't behave properly without it.

Appending to $@ without a move is OK here because we're using the .DELETE_ON_ERROR Makefile feature. See 7b76d6bf221 (Makefile: add and use the ".DELETE_ON_ERROR" flag, 2021-06-29). GNU make ensures that on error this file will be removed.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
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 .gitignore | 1 +
 Makefile   | 8 +++++---
 2 files changed, 6 insertions(+), 3 deletions(-)