[cdt-dev] Considerable gnu make speedup with disabled implicit rules

[Raphael Zulliger <zulliger@xxxxxxxx>]

Hi

Is there any reason, why we don't turn off gnu makes "implicit rules" 
(make -r) for the gnu makefile builder in CDT? It seems to significantly 
speedup make!
  According to my understanding, the goal of the CDT toolchain 
definitions and the makefile generator is to define explicit rules for 
everything it needs to build and therefore, implicit rules are useless 
in our case (although I'm not very sure about that statement).

Running make on a projects which was already built (aka up-to-date) with 
disabled implicit rules gave me speedups of more than factor 10! (~12 
seconds vs. ~1 second) in the following use case:
  C++ project (~1500 .cpp files) on a Windows 7 64bit (running within 
VMWare) 2 years old Mac Book Pro with conventional harddisk (no SSD) 
using a mingw-built gnu make 3.82. (Side-note: On my Linux box, make is 
much faster and therefore the "-r" option doesn't help as much as on 
Windows.)

I was investigating in speeding up make because waiting ~12 second for 
make just to know that nothing needs to be built is an annoyingly long 
time... (note: it also takes ~12 seconds until make executes the first 
instance of the compiler when the project is not up-to-date). 
Personally, I hope that we could change the default behavior to use -r 
in order to improve user experience with CDT. If desired, I'll open a 
bugzilla for this.

Raphael