Should the build system use ar rcs instead of ranlib + ar rc?

[Andrew Pinski]

On Fri, Jul 15, 2016 at 6:46 PM, Patrick Palka <patrick@parcs.ath.cx> wrote:
> The build step that invokes "ranlib libbackend.a" (which immediately
> follows the invocation of "ar rc libbackend.a ...") takes over 7 seconds
> on my machine and causes the entire 450MB archive to be rewritten.  By
> instead making the build system use ar rcs -- so that the archive and
> its index are built at once -- the time it takes for the compiler to get
> rebuilt gets reduced by 25%, from 27s to 20s (in a --disable-bootstrap
> tree after touching a random source file).  This is a pretty significant
> reduction in compile time and disk io.
>
> Is this a good idea?

Yes and no.  Do we know if all ar support rcs now?  Or is it just binutils's ar?

Thanks,
Andrew


>
> Here's the patchlet I used:
>
> -- >8 --
>
> diff --git a/Makefile.in b/Makefile.in
> index 117fbf5..5ebc3a3 100644
> --- a/Makefile.in
> +++ b/Makefile.in
> @@ -393,7 +393,7 @@ MAKEINFOFLAGS = --split-size=5000000
>
>  AS = @AS@
>  AR = @AR@
> -AR_FLAGS = rc
> +AR_FLAGS = rcs
>  CC = @CC@
>  CXX = @CXX@
>  DLLTOOL = @DLLTOOL@
> diff --git a/Makefile.tpl b/Makefile.tpl
> index 94a4f79..72ba24b 100644
> --- a/Makefile.tpl
> +++ b/Makefile.tpl
> @@ -396,7 +396,7 @@ MAKEINFOFLAGS = --split-size=5000000
>
>  AS = @AS@
>  AR = @AR@
> -AR_FLAGS = rc
> +AR_FLAGS = rcs
>  CC = @CC@
>  CXX = @CXX@
>  DLLTOOL = @DLLTOOL@
> diff --git a/gcc/Makefile.in b/gcc/Makefile.in
> index 0786fa3..1c3a637 100644
> --- a/gcc/Makefile.in
> +++ b/gcc/Makefile.in
> @@ -236,7 +236,7 @@ BISONFLAGS =
>  FLEX = @FLEX@
>  FLEXFLAGS =
>  AR = @AR@
> -AR_FLAGS = rc
> +AR_FLAGS = rcs
>  NM = @NM@
>  RANLIB = @RANLIB@
>  RANLIB_FLAGS = @ranlib_flags@
> @@ -1883,17 +1883,14 @@ compilations: $(BACKEND)
>  libbackend.a: $(OBJS)
>         -rm -rf libbackend.a
>         $(AR) $(AR_FLAGS) libbackend.a $(OBJS)
> -       -$(RANLIB) $(RANLIB_FLAGS) libbackend.a
>
>  libcommon-target.a: $(OBJS-libcommon-target)
>         -rm -rf libcommon-target.a
>         $(AR) $(AR_FLAGS) libcommon-target.a $(OBJS-libcommon-target)
> -       -$(RANLIB) $(RANLIB_FLAGS) libcommon-target.a
>
>  libcommon.a: $(OBJS-libcommon)
>         -rm -rf libcommon.a
>         $(AR) $(AR_FLAGS) libcommon.a $(OBJS-libcommon)
> -       -$(RANLIB) $(RANLIB_FLAGS) libcommon.a
>
>  # We call this executable `xgcc' rather than `gcc'
>  # to avoid confusion if the current directory is in the path