On 27.12.2012 17:53, Simon Urbanek wrote:
On Dec 23, 2012, at 9:22 PM, Matthew Dowle wrote:
Hi,
Similar questions have come up before on the list and elsewhere but
I haven't found a solution yet.
winbuilder's install.out shows data.table's .c files compiled with
-O3 on Win32 but -O2 on Win64. The same happens on R-Forge. I gather
that some packages don't work with -O3 so the default is -O2.
I've tried this in data.table's Makevars (entire contents) :
====
MAKEFLAGS="CFLAGS=-O3" # added
CFLAGS=-O3 # added
PKG_CFLAGS=-O3 # added
all: $(SHLIB) # no change
mv $(SHLIB) datatable$(SHLIB_EXT) # no change
====
but -O2 still appears in winbuilder's install.out (after -O3, and I
believe the last -O is the one that counts) :
gcc -m64 -I"D:/RCompile/recent/R-2.15.2/include" -DNDEBUG
-I"d:/Rcompile/CRANpkg/extralibs215/local215/include" -O3 -O2 -Wall
-std=gnu99 -mtune=core2 -c dogroups.c -o dogroups.o
How can I ensure that data.table is compiled with -O3 on Win64?
You can't - at least not in a way that doesn't circumvent the R build
system. Also it's not portable so you don't want to mess with
optimization flags and hard-code it in your package as it's user's
choice how they setup R and its flags. You can certainly setup your R
to compile with -O3, you just can't impose that on others.
Cheers,
Simon
Thanks Simon. This makes complete sense where users compile packages on
install (Unix and Mac, and I better check my settings then), but on
Windows where it's more common for the user to install the pre-compiled
.zip from CRAN is my concern. This came up because the new fread
function in data.table wasn't showing as much of a speedup on Win64 as
on Linux. I'm not 100% sure that non -O3 is the cause, but there are
some function calls which get iterated a lot (e.g. isspace) and I'd seen
that inlining was something -O3 did and not -O2.
In general, why wouldn't a user of a package want the best performance
from -O3? By non portable do you mean the executable produced by
winbuilder (or by CRAN) might not run on all Windows machines it's
installed on (because -O3 (over) optimizes for the machine it's built
on), or do you mean that -O3 itself might not be available on some
compilers (and if so which compilers don't have -O3?).
Thanks, Matthew
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