Bug 171075

Summary: Air should support callsite-saves
Product: WebKit Reporter: Filip Pizlo <fpizlo>
Component: JavaScriptCoreAssignee: Filip Pizlo <fpizlo>
Status: RESOLVED WONTFIX    
Severity: Normal    
Priority: P2    
Version: WebKit Nightly Build   
Hardware: All   
OS: All   
Attachments:
Description Flags
it builds!
none
full attempt none

Filip Pizlo
Reported 2017-04-20 14:12:45 PDT
Callsite-saves are an optimization that I found to be useful in a previous compiler project. Basically, if you find that some register file needs callee-saves, but the ABI doesn't give them to you, you can fake it in the compiler: just designate some registers callsite-save and then do: - Ignore those registers if they appear in the clobber set for any instruction during interference graph building. Note that if an instruction defs a callsite-save, it still gets interference. - After register allocation completes, emit save/restore code around any instruction that clobbers but does not def a callsite save. I previously found this to be a >=30% speed-up on some floating-point code (some raytracer written in Java) on x86-32 when compiling to cdecl, which has no floating point callee-saves. I used 3 callsite-saves in that project. It's worth trying at B3 -O2.
Attachments
it builds! (31.51 KB, patch)
2017-04-20 14:16 PDT, Filip Pizlo 		no flags
DetailsFormatted DiffDiff
full attempt (45.86 KB, patch)
2017-04-21 11:51 PDT, Filip Pizlo 		no flags
DetailsFormatted DiffDiff
Show Obsolete (1) View All Add attachment proposed patch, testcase, etc.
Filip Pizlo
Comment 1 2017-04-20 14:16:06 PDT
Created attachment 307636 [details] it builds!
Filip Pizlo
Comment 2 2017-04-21 11:51:51 PDT
Created attachment 307764 [details] full attempt This is neutral on everything except Kraken, where it's a 1% regression. I guess we don't need it.
Filip Pizlo
Comment 3 2017-04-21 11:52:10 PDT
It's not a progression, so we shouldn't do it.
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