[lld] r228077 - Simplify large switches.
Sean Silva
chisophugis at gmail.com
Wed Feb 4 18:04:45 PST 2015
On Wed, Feb 4, 2015 at 2:02 PM, Rui Ueyama <ruiu at google.com> wrote:
> Comment is back in r228201.
>
> As to the performance, LLD took 200 *microseconds* in
> GnuLdDriver::evaluateLinkerScript when linking itself on Linux (it parsed
> 600 bytes of data). And these functions are only a small part of the entire
> process. It's really negligible.
>
We use a linker script when self-hosting?
-- Sean Silva
>
> On Tue, Feb 3, 2015 at 10:29 PM, Chandler Carruth <chandlerc at google.com>
> wrote:
>
>> Comments are great, but I do much prefer the 'strchr' interface. So lets
>> go with comments and a strchr interface.
>>
>> If this doesn't generate good code for some reason (no idea, haven't
>> checked) we could either teach LLVM to generate awesome code for it or we
>> could provide our own strchr-like utility that generates awesome code....
>> But i'd like to see evidence that the performance of these is critical.
>>
>> On Tue, Feb 3, 2015 at 9:21 PM, Philip Reames <listmail at philipreames.com>
>> wrote:
>>
>>> To me the first change is a readability regression (lost comments if
>>> nothing else); the later two are neutral. I don't have a strong
>>> preference, but please preserve the comments from the first function if
>>> nothing else.
>>>
>>> p.s. Has anyone checked if we convert these strchrs to the "obvious"
>>> bits of code? Each of these should be nearly as fast as the original
>>> switches provided they're optimized correctly.
>>>
>>>
>>> On 02/03/2015 06:33 PM, Shankar Easwaran wrote:
>>>
>>>> The style used in the old code is followed in clang too in various
>>>> places. I felt its more readable too.
>>>>
>>>> This makes it less performant even if its not in performance critical
>>>> pass and less readable too.
>>>>
>>>> Shankar Easwaran
>>>>
>>>> On 2/3/2015 6:00 PM, Rui Ueyama wrote:
>>>>
>>>>> Author: ruiu
>>>>> Date: Tue Feb 3 18:00:21 2015
>>>>> New Revision: 228077
>>>>>
>>>>> URL: http://llvm.org/viewvc/llvm-project?rev=228077&view=rev
>>>>> Log:
>>>>> Simplify large switches.
>>>>>
>>>>> This may be a little bit inefficient than the original code
>>>>> but that should be okay as this is not really in a performance
>>>>> critical pass.
>>>>>
>>>>> http://reviews.llvm.org/D7393
>>>>>
>>>>> Modified:
>>>>> lld/trunk/lib/ReaderWriter/LinkerScript.cpp
>>>>>
>>>>> Modified: lld/trunk/lib/ReaderWriter/LinkerScript.cpp
>>>>> URL: http://llvm.org/viewvc/llvm-project/lld/trunk/lib/
>>>>> ReaderWriter/LinkerScript.cpp?rev=228077&r1=228076&r2=228077&view=diff
>>>>> ==============================================================================
>>>>>
>>>>> --- lld/trunk/lib/ReaderWriter/LinkerScript.cpp (original)
>>>>> +++ lld/trunk/lib/ReaderWriter/LinkerScript.cpp Tue Feb 3 18:00:21
>>>>> 2015
>>>>> @@ -242,66 +242,17 @@ bool Lexer::canStartNumber(char c) const
>>>>> }
>>>>> bool Lexer::canContinueNumber(char c) const {
>>>>> - switch (c) {
>>>>> - // Digits
>>>>> - case '0': case '1': case '2': case '3': case '4': case '5': case
>>>>> '6':
>>>>> - case '7': case '8': case '9':
>>>>> - case 'A': case 'B': case 'C': case 'D': case 'E': case 'F':
>>>>> - case 'a': case 'b': case 'c': case 'd': case 'e': case 'f':
>>>>> - // Hex marker
>>>>> - case 'x': case 'X':
>>>>> - // Type suffix
>>>>> - case 'h': case 'H': case 'o': case 'O':
>>>>> - // Scale suffix
>>>>> - case 'M': case 'K':
>>>>> - return true;
>>>>> - default:
>>>>> - return false;
>>>>> - }
>>>>> + return strchr("0123456789ABCDEFabcdefxXhHoOMK", c);
>>>>> }
>>>>> bool Lexer::canStartName(char c) const {
>>>>> - switch (c) {
>>>>> - case 'A': case 'B': case 'C': case 'D': case 'E': case 'F': case
>>>>> 'G':
>>>>> - case 'H': case 'I': case 'J': case 'K': case 'L': case 'M': case
>>>>> 'N':
>>>>> - case 'O': case 'P': case 'Q': case 'R': case 'S': case 'T': case
>>>>> 'U':
>>>>> - case 'V': case 'W': case 'X': case 'Y': case 'Z':
>>>>> - case 'a': case 'b': case 'c': case 'd': case 'e': case 'f': case
>>>>> 'g':
>>>>> - case 'h': case 'i': case 'j': case 'k': case 'l': case 'm': case
>>>>> 'n':
>>>>> - case 'o': case 'p': case 'q': case 'r': case 's': case 't': case
>>>>> 'u':
>>>>> - case 'v': case 'w': case 'x': case 'y': case 'z':
>>>>> - case '_': case '.': case '$': case '/': case '\\':
>>>>> - case '*':
>>>>> - return true;
>>>>> - default:
>>>>> - return false;
>>>>> - }
>>>>> + return strchr(
>>>>> + "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_.$/\\*", c);
>>>>> }
>>>>> bool Lexer::canContinueName(char c) const {
>>>>> - switch (c) {
>>>>> - case 'A': case 'B': case 'C': case 'D': case 'E': case 'F': case
>>>>> 'G':
>>>>> - case 'H': case 'I': case 'J': case 'K': case 'L': case 'M': case
>>>>> 'N':
>>>>> - case 'O': case 'P': case 'Q': case 'R': case 'S': case 'T': case
>>>>> 'U':
>>>>> - case 'V': case 'W': case 'X': case 'Y': case 'Z':
>>>>> - case 'a': case 'b': case 'c': case 'd': case 'e': case 'f': case
>>>>> 'g':
>>>>> - case 'h': case 'i': case 'j': case 'k': case 'l': case 'm': case
>>>>> 'n':
>>>>> - case 'o': case 'p': case 'q': case 'r': case 's': case 't': case
>>>>> 'u':
>>>>> - case 'v': case 'w': case 'x': case 'y': case 'z':
>>>>> - case '0': case '1': case '2': case '3': case '4': case '5': case
>>>>> '6':
>>>>> - case '7': case '8': case '9':
>>>>> - case '_': case '.': case '$': case '/': case '\\': case '~': case
>>>>> '=':
>>>>> - case '+':
>>>>> - case '[':
>>>>> - case ']':
>>>>> - case '*':
>>>>> - case '?':
>>>>> - case '-':
>>>>> - case ':':
>>>>> - return true;
>>>>> - default:
>>>>> - return false;
>>>>> - }
>>>>> + return strchr("ABCDEFGHIJKLMNOPQRSTUVWXYZabcd
>>>>> efghijklmnopqrstuvwxyz"
>>>>> + "0123456789_.$/\\~=+[]*?-:", c);
>>>>> }
>>>>> /// Helper function to split a StringRef in two at the nth
>>>>> character.
>>>>>
>>>>>
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>>>>>
>>>>>
>>>>>
>>>>
>>>>
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