[llvm-commits] X86 FastISel: Emit immediate call arguments locally to save stack size when compiling with -O0

[Jakob Stoklund Olesen]

On Aug 11, 2011, at 9:36 AM, Ivan Krasin wrote:

> https://spreadsheets.google.com/a/google.com/spreadsheet/ccc?key=0Ao3TPgpIlZ9ddHVpeDVCSzZHYXlJOTc0N1VKX1BFNVE&hl=en_US#gid=0

Thanks. Those numbers look really good, except for:

> There're few major regressions which I believe a show stopper for this
> patch (the top of the spreadsheet above):
> 
> objinst.llvm.bc	272	344	0	0.0027	245	184	0	0.0026	11.02%	86.96%	0.10%
> cast.linked.bc	1053	1224	0	0.0058	924	664	0	0.0051	13.96%	84.34%	0.67%
> cast.llvm.bc	1053	1224	0	0.0057	926	680	0	0.005	13.71%	80.00%	0.67%
> objinst.linked.bc	320	360	0	0.0038	301	232	0	0.0036	6.31%	55.17%	0.19%
> 
> The second column from right is stack size increase if patch is applied.
> 
> All of these examples could be described as "one global constant is
> used across many calls in one function".
> Probably, the fix should be "don't apply an optimization if the block
> uses global variables", but I'm not sure if it would help too much.

I don't understand how your patch can increase the stack space used. How does that happen? What is getting spilled?

/jakob