Review request (s): 7116081: USE_PRECOMPILED_HEADER=0 triggers a single threaded build of the JVM

[Stefan Karlsson]

David,

Thanks for the review.

All,

Updated webrev: http://cr.openjdk.java.net/~stefank/7116081/webrev.2/

The rationale for this change is inlined:

On 11/29/2011 12:48 AM, David Holmes wrote:
> Hi Stefan,
>
> On 29/11/2011 12:34 AM, Stefan Karlsson wrote:
>> http://cr.openjdk.java.net/~stefank/7116081/webrev/
>>
>> Turning off the precompiled headers is somewhat broken. It triggers a
>> single threaded build even when HOTSPOT_BUILD_JOBS has been set. With
>> this fix the compile times went from around 14 minutes to 2.5 minutes,
>> on an 8 core machine.
>
> Took me a while to figure out why this was the case :)
>
>> This affects both Linux and BSD builds, but has only been tested on
>> Linux. It would be great if someone with access to a BSD machine could
>> verify this fix.
>
> The problem here was using
>
> ifdef USE_PRECOMPILED_HEADER
>
> when defining it to 0 is used to turn it off - so it seems to me the 
> better fix here was to simply change to:
>
> ifeq ($(USE_PRECOMPILED_HEADER),1)

I've changed the conditional to check USE_PRECOMPILED_HEADER instead.

While doing that I found another issue. In gcc.make we try to redefine 
USE_PRECOMPILED_HEADER:

  88 ifneq ($(USE_PRECOMPILED_HEADER),0)
  89 USE_PRECOMPILED_HEADER=1


That doesn't work, so setting USE_PRECOMPILED_HEADER=<arbitrary string 
(not 0)> on the command line will leave the precompiled headers on, but 
later logic:

  219 ifneq ($(USE_PRECOMPILED_HEADER),1)
  220 CFLAGS += -DDONT_USE_PRECOMPILED_HEADER

will empty the precompiled.hpp file. From precompiled.hpp:

// Precompiled headers are turned off for Sun Studion,
// or if the user passes USE_PRECOMPILED_HEADER=0 to the makefiles.
#ifndef DONT_USE_PRECOMPILED_HEADER

In the new webrev I've changed all places where we read 
USE_PRECOMPILED_HEADER to always compare against 0.

thanks,
StefanK

>
>
> The removal of:
>
> PrecompiledOption = -DUSE_PRECOMPILED_HEADER
>
> seems okay.
>
> Cheers,
> David
>
>