0005133: Improve float allocation

View Issue Details [ Jump to Notes ]

[ Issue History ] [ Print ]

Project

Category

View Status

Date Submitted

Last Update

0005133

OCaml

OCaml backend (code generation)

public

2010-08-23 15:40

2012-06-21 20:10

Reporter

Christophe Troestler

Assigned To

Priority

normal

Severity

feature

Reproducibility

always

Status

acknowledged

Resolution

open

Platform

OS Version

Product Version

3.13.0+dev

Target Version

Fixed in Version

Summary

0005133: Improve float allocation

Description

There have been a number of significant improvements in float handling in 3.12 but the following example shows on could go further:

Program 1 ------------------------------
let r = ref 0.0 in
for i = 0 to 1000_000_000 do r := float i done;
Printf.printf "%f\n" !r;
Printf.printf "words: %f\n" (Gc.stat ()).Gc.minor_words

1000000000.000000
words: 2000000363.000000
2.79user 0.00system 0:02.79elapsed 99%CPU (0avgtext+0avgdata 4208maxresident)k
0inputs+0outputs (0major+313minor)pagefaults 0swaps

Program 2 ------------------------------
let r = ref 0.0 in
for i = 0 to 1000_000_000 do r := float i done;
Printf.printf "%f\n" (!r +. 0.);
Printf.printf "words: %f\n" (Gc.stat ()).Gc.minor_words

1000000000.000000
words: 363.000000
1.20user 0.00system 0:01.20elapsed 99%CPU (0avgtext+0avgdata 3152maxresident)k
0inputs+0outputs (0major+247minor)pagefaults 0swaps
----------------------------------------
The second version allocates much less and is way faster on my machine (Linux poincare 2.6.35 #1 SMP Fri Aug 20 14:34:25 CEST 2010 x86_64 GNU/Linux). Both programs were compiled to native code. It would be nice not to have to resort to such tricks to improve performance! Couldn't the compiler figure out this optimization?

Tags

No tags attached.

Attached Files

Relationships

child of

0005204

acknowledged

Unboxing parameters and more kinds of local bindings

Notes
(0007344) Christophe Troestler (reporter) 2012-04-12 19:27	See also bug 0005204.

(0007345) frisch (developer) 2012-04-12 19:49	Indeed, this is a typical case where the boxing/unboxing strategy proposed in 0005204 works nicely and avoids having to force manually the unboxing by adding an ad hoc "+. 0.".

Issue History
Date Modified	Username	Field	Change
2010-08-23 15:40	Christophe Troestler	New Issue
2011-05-20 17:56	doligez	Status	new => acknowledged
2012-04-12 19:27	Christophe Troestler	Note Added: 0007344
2012-04-12 19:47	frisch	Relationship added	child of 0005204
2012-04-12 19:49	frisch	Note Added: 0007345
2012-06-21 20:10	frisch	Category	OCaml general => OCaml backend (code generation)