Re: C++ demangler fix

[Jakub Jelinek <jakub at redhat dot com>]

On Wed, Sep 11, 2013 at 01:49:46PM +0100, Gary Benson wrote:
> Jakub Jelinek wrote:
> > cp-demangle.c isn't used just in libiberty, where using hashtab,
> > xcalloc, XNEW etc. is fine, but also in libsupc++/libstdc++, where
> > none of that is fine.  That is why cp-demangle.c only uses
> > e.g. realloc, checks for allocation failures and propagates those to
> > the caller if they happen (see allocation_failure field).  hashtab.o
> > isn't linked into libstdc++ nor libsupc++, and the question is if we
> > really do want to link all the hashtable code into libstdc++.
> > How many hash table entries are there typically?  Is a hashtable
> > required?
> 
> Three entries were required for the symbol in the testcase:
> 
>   "_ZSt7forwardIRN1x14refobjiteratorINS0_3refINS0_4mime30multipart_se" \
>   "ction_processorObjIZ15get_body_parserIZZN14mime_processor21make_se" \
>   "ction_iteratorERKNS2_INS3_10sectionObjENS0_10ptrrefBaseEEEbENKUlvE" \
>   "_clEvEUlSB_bE_ZZNS6_21make_section_iteratorESB_bENKSC_clEvEUlSB_E0" \
>   "_ENS1_INS2_INS0_20outputrefiteratorObjIiEES8_EEEERKSsSB_OT_OT0_EUl" \
>   "mE_NS3_32make_multipart_default_discarderISP_EEEES8_EEEEEOT_RNSt16" \
>   "remove_referenceISW_E4typeE"
> 
> I don't think there will many symbols with very many entries required.
> I'm guessing that most symbols will require zero (which is why I made
> it defer hashtable creation until it was required).
> 
> What kind of data structure would you like to see here, a realloc'd
> array?  Do libsupc++ and libstdc++ use the demangler for anything more
> performance-sensitive than exception printing?

I don't know, I guess it isn't very performance sensitive, especially
if it is very rare to need too many of the scopes (at least on real-world
symbols, of course somebody can try to demangle something artificially
hacked up).

	Jakub