Accelerate the 'configure' script

[R. Diez]

Hi all:

I have this cross-compiling Autoconf project:

https://github.com/rdiez/JtagDue/tree/master/Project

I am not using Autoconf for portability, but mainly for handling C/C++ 
dependencies, so that not everything is rebuilt when I change one source file.

This is just an example project, I have others that are bigger, and I rebuild 
many of them automatically overnight. That is why I am looking at speeding up 
the configuration process.

The example project above does the following checks:

checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for arm-none-eabi-strip... arm-none-eabi-strip
checking for a race-free mkdir -p... /bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking whether make supports nested variables... yes
checking whether make supports nested variables... (cached) yes
checking for arm-none-eabi-gcc... ccache arm-none-eabi-gcc
checking whether we are cross compiling... yes
checking for suffix of object files... o
checking whether the compiler supports GNU C... yes
checking whether ccache arm-none-eabi-gcc accepts -g... yes
checking for ccache arm-none-eabi-gcc option to enable C11 features... none 
needed
checking whether ccache arm-none-eabi-gcc understands -c and -o together... yes
checking whether make supports the include directive... yes (GNU style)
checking dependency style of ccache arm-none-eabi-gcc... gcc3
checking whether the compiler supports GNU C++... yes
checking whether ccache arm-none-eabi-g++ accepts -g... yes
checking for ccache arm-none-eabi-g++ option to enable C++11 features... none 
needed
checking dependency style of ccache arm-none-eabi-g++... gcc3
checking dependency style of ccache arm-none-eabi-gcc... gcc3
checking for arm-none-eabi-ranlib... arm-none-eabi-gcc-ranlib

Is there a way to speed these checks up? The platform is always a reasonably 
modern Linux, the compiler is always GCC, and ccache is always at least version 
3.7.7, so most checks are unnecessary (for me).

Things I can think of:

- 'install' can be assumed to be OK.
- 'mkdir' can be assumed to be OK.
- I am always using GNU Make, so all 3 checks around make are dispensable.
- I am always using GCC, so checking whether it accepts -g etc. is not 
necessary.

Is there any article or blog post somewhere with speed-up hints for Autoconf?


I am aware that Autoconf has an optional config cache, but this time I am 
specifically looking for other ways.

One of the problems of the config cache is that I cannot share a config.cache for all 
possible build types of one project, let alone different projects. What I mean is that, 
if I configure the project above in different out-of-tree subdirectories (one for an ARM 
target as a debug build, another one for an Intel target as a release build, etc.), then 
I cannot easily share a global configure.cache with only the result of global checks like 
"whether mkdir -p" is race free.

Even if I managed to share one config.cache, I am not sure that multiple 
projects building in parallel would not corrupt it (race condition). That is 
not documented as far as I can tell.

I could try to generate a fake cache file, but that is not straightforward, and 
it is always somewhat brittle. For example, you cannot easily guarantee that 
the pre-calculated cache entries are actually being used by the next Autoconf 
version.

Thanks in advance,
  rdiez