* Re: -fno-rtti [not found] <20000313103358.C25605@neel> @ 2000-03-13 11:20 ` llewelly 2000-04-01 0:00 ` -fno-rtti llewelly 0 siblings, 1 reply; 2+ messages in thread From: llewelly @ 2000-03-13 11:20 UTC (permalink / raw) To: Neelakanth Nadgir; +Cc: gcc-help On Mon, 13 Mar 2000, Neelakanth Nadgir wrote: > > Hi, > a quick question, I believe gcc@gcc.gnu.org is for gcc developer concerns; gcc-help@gcc.gnu.org is more apropriate for this question. > If a code uses RTTI, can it be compiled with -fno-rtti ? No. RTTI requires type_info nodes, which it uses to identify types at runtime. For example, dynamic_cast<> works by comparing type_info nodes. If you compile code which uses dynamic_cast<> or typeid with -fno-rtti, g++ will generate an error. > > Why is it that for some codes -fno-rtti decreases codesize by as > much as 5x? Every type in a C++ program needs a type_info node. C++ programs often contain many, many types. Thus the size increase. However, in my experience, I do not think I have ever seen 5x increase; 15-30% (1.15x to 1.3x) is more common. [snip] ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: -fno-rtti 2000-03-13 11:20 ` -fno-rtti llewelly @ 2000-04-01 0:00 ` llewelly 0 siblings, 0 replies; 2+ messages in thread From: llewelly @ 2000-04-01 0:00 UTC (permalink / raw) To: Neelakanth Nadgir; +Cc: gcc-help On Mon, 13 Mar 2000, Neelakanth Nadgir wrote: > > Hi, > a quick question, I believe gcc@gcc.gnu.org is for gcc developer concerns; gcc-help@gcc.gnu.org is more apropriate for this question. > If a code uses RTTI, can it be compiled with -fno-rtti ? No. RTTI requires type_info nodes, which it uses to identify types at runtime. For example, dynamic_cast<> works by comparing type_info nodes. If you compile code which uses dynamic_cast<> or typeid with -fno-rtti, g++ will generate an error. > > Why is it that for some codes -fno-rtti decreases codesize by as > much as 5x? Every type in a C++ program needs a type_info node. C++ programs often contain many, many types. Thus the size increase. However, in my experience, I do not think I have ever seen 5x increase; 15-30% (1.15x to 1.3x) is more common. [snip] ^ permalink raw reply [flat|nested] 2+ messages in thread
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