[llvm] r238104 - Bump SmallString to the minimum required amount for raw_ostream to avoid allocation.

[Yaron Keren]

grow() does the power of 2 thing, probably to avoid quadratic behaviour

http://llvm.org/klaus/llvm/blob/master/include/llvm/ADT/SmallVector.h#L-248


2015-05-29 2:00 GMT+03:00 Sean Silva <chisophugis at gmail.com>:

>
>
> On Thu, May 28, 2015 at 2:48 AM, Benjamin Kramer <benny.kra at gmail.com>
> wrote:
>
>> On Thu, May 28, 2015 at 3:25 AM, Sean Silva <chisophugis at gmail.com>
>> wrote:
>> >
>> >
>> > On Wed, May 27, 2015 at 6:24 PM, Sean Silva <chisophugis at gmail.com>
>> wrote:
>> >>
>> >> I've always thought that it was confusing that SmallString internally
>> did
>> >> so much processing on the number you give it to actually choose the
>> buffer
>> >> size. Maybe we can just static_assert it is a power of 2 so it is
>> always
>> >> WYSIWYG?
>> >
>> >
>> > (and all the other conditions it does, such as requiring 0 to mean "no
>> > buffer")
>>
>> Does it really modify the buffer size internally? I thought it just
>> forwarded to SmallVector, which shouldn't be restricted to powers of
>> 2.
>>
>
> Hmm.. not sure what I was remembering. I seem to recall SmallVector would
> always round the buffer size to a power of 2, but I guess not:
> http://llvm.org/klaus/llvm/blob/master/include/llvm/ADT/SmallVector.h#L-843
> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_klaus_llvm_blob_master_include_llvm_ADT_SmallVector.h-23L-2D843&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=9Q11tH9G2gqowmFtkwbMQvXQv-nLf4pqSkShmPhoQ2k&s=ZmHY7mQg1FsH1YGgmlOicA8YRpZ67UevR-BxlNMGVLE&e=>
>
>
> -- Sean Silva
>
>
>> This commit was about raw_svector_ostream always allocating 128 bytes
>> when its created, rendering the 60 bytes of inline storage completely
>> useless. This is very annoying but I have no idea how to fix it.
>>
>> - Ben
>>
>> >>
>> >> On Sat, May 23, 2015 at 10:20 AM, Benjamin Kramer
>> >> <benny.kra at googlemail.com> wrote:
>> >>>
>> >>> Author: d0k
>> >>> Date: Sat May 23 12:20:53 2015
>> >>> New Revision: 238104
>> >>>
>> >>> URL: http://llvm.org/viewvc/llvm-project?rev=238104&view=rev
>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D238104-26view-3Drev&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=9Q11tH9G2gqowmFtkwbMQvXQv-nLf4pqSkShmPhoQ2k&s=68kVpHm58qHqnifgI4sZAKvLwQHhJiTDfkcRB2NJX_0&e=>
>> >>> Log:
>> >>> Bump SmallString to the minimum required amount for raw_ostream to
>> avoid
>> >>> allocation.
>> >>>
>> >>> NFC.
>> >>>
>> >>> Modified:
>> >>>     llvm/trunk/lib/Target/TargetMachine.cpp
>> >>>
>> >>> Modified: llvm/trunk/lib/Target/TargetMachine.cpp
>> >>> URL:
>> >>>
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/TargetMachine.cpp?rev=238104&r1=238103&r2=238104&view=diff
>> <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_lib_Target_TargetMachine.cpp-3Frev-3D238104-26r1-3D238103-26r2-3D238104-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=9Q11tH9G2gqowmFtkwbMQvXQv-nLf4pqSkShmPhoQ2k&s=cyhaMAOkJrpQl0TWmHbwVXKICaMpb028BvNSV3IfxZw&e=>
>> >>>
>> >>>
>> ==============================================================================
>> >>> --- llvm/trunk/lib/Target/TargetMachine.cpp (original)
>> >>> +++ llvm/trunk/lib/Target/TargetMachine.cpp Sat May 23 12:20:53 2015
>> >>> @@ -185,7 +185,7 @@ void TargetMachine::getNameWithPrefix(Sm
>> >>>  }
>> >>>
>> >>>  MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV, Mangler
>> &Mang)
>> >>> const {
>> >>> -  SmallString<60> NameStr;
>> >>> +  SmallString<128> NameStr;
>> >>>    getNameWithPrefix(NameStr, GV, Mang);
>> >>>    const TargetLoweringObjectFile *TLOF = getObjFileLowering();
>> >>>    return TLOF->getContext().getOrCreateSymbol(NameStr);
>> >>>
>> >>>
>> >>> _______________________________________________
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>> >>
>> >>
>> >
>>
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