On Fri, Mar 15, 2019 at 8:42 AM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote: > > During a simple no-op (nothing changed) build I saw 39 invocations of > the C compiler with the argument "-print-file-name=include". We don't > need to call the C compiler 39 times for this--one time will suffice. > > Let's change NOSTDINC_FLAGS to a simply expanded variable to avoid > this since there doesn't appear to be any reason it should be > recursively expanded. > > On my build this shaved ~400 ms off my "no-op" build. > > Note that the recursive expansion seems to date back to the (really > old) commit e8f5bdb02ce0 ("[PATCH] Makefile include path ordering"). > It's a little unclear to me if the point of that patch was to switch > the variable to be recursively expanded (which it did) or to avoid > directly assigning to NOSTDINC_FLAGS (AKA to switch to +=) because > someone else (out of tree?) was setting it. I presume later since if > the only goal was to switch to recursive expansion the patch would > have just removed the ":". > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> Applied to linux-kbuild. Thanks. > --- > > Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/Makefile b/Makefile > index 9ef547fc7ffe..3034ba66ad51 100644 > --- a/Makefile > +++ b/Makefile > @@ -402,7 +402,7 @@ CHECK = sparse > > CHECKFLAGS := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \ > -Wbitwise -Wno-return-void -Wno-unknown-attribute $(CF) > -NOSTDINC_FLAGS = > +NOSTDINC_FLAGS := > CFLAGS_MODULE = > AFLAGS_MODULE = > LDFLAGS_MODULE = > -- > 2.21.0.360.g471c308f928-goog > -- Best Regards Masahiro Yamada