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Re: PR/15448: add a compiler timestamp to PCH files (take 3)


Mike Stump wrote:
On Feb 18, 2005, at 5:41 AM, Paolo Bonzini wrote:

Like the attached patch?


Ah, interesting... my main concern would be speed and size of the PCH file. If this only adds 1% or less and under 25ms, then, I don't have a problem with it.

It adds a fixed 2.5 kb to the PCH. I have not timed it, but reading and comparing 2.5 kb should be less than 2 million clock cycles (it depends a little on the vagaries of the OS since we use read instead of stdio).


Responding to Geoff, the patch *does* check things that affect PCH. While checking a single variable would have taken into account the size of the binary (if variables are stored in memory after the text segment, which they usually are), what about:

1) a struct whose size changes

2) inner pointers to other GTY globals

3) added or deleted variables (which would result in the whole rtab sliding by one or more entries).

All these invalidate the PCH.

Paolo


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