Perl优化器问题:Perl编译器会优化掉所有这些临时变量吗? [英] Perl optimizer question: Will the perl compiler optimize away all of these temporary variables?

问题描述

我有一个非常简单的算法，但是出于可读性和正确性，我将其扩展为一堆临时变量.更容易阅读，更改和检查表达式的部分内容.

I've got a pretty simple piece of arithmetic, but for readability and correctness, I've expanded it out into a bunch of temporary variables. It's easier to read, change, and examine partial pieces of the expression.

我的问题是，这段代码会不会因为扩展而在运行时被击败?我不知道perl编译器是如何工作的，但是在"C"之类的情况下，这些多余的(不太完全)的变量将不存在而被优化.

My question is, will this code take a run-time beating just because it's expanded? I don't know how the perl compiler works, but in 'C', or such, these extra (not quite) variables would be optimized right out of existence.

my $targetBasis = $$s{"basis"} * $nextBasisPct;
my $dollarsHeld = $$s{"basis"} * $$s{"held"};
my $targetDollars = $dollarsHeld + $opt{"buyDollars"};
my $targetShares = $targetDollars / $targetBasis;
my $newShares = $targetShares - $$s{"held"};
my $targetPrice = $opt{"buyDollars"} / $newShares;

谢谢.

-E

我刚刚完成了从一个看起来讨厌的班轮的扩展，只是发现它是正确的.如果没有理由，我宁愿不要将其放回无法阅读的状态.

I just got done expanding this from a nasty looking one liner, only to find that it was correct. I'd rather not put it back to unreadable if there's no reason to do so.

推荐答案

否.

以下程序的编译版本

$ perl -MO=Concise,-exec a.pl
1  <0> enter
2  <;> nextstate(main 2 a.pl:2) v:*,&,{,x*,x&,x$,$
3  <0> padrange[$s:2,8; %opt:2,8; $targetBasis:2,8] vM/LVINTRO,range=3
4  <;> nextstate(main 3 a.pl:3) v:*,&,{,x*,x&,x$,$
5  <+> multideref($s->{"basis"}) sK/STRICT
6  <+> multideref($s->{"held"}) sK/STRICT
7  <2> multiply[t5] sK/2
8  <0> padsv[$dollarsHeld:3,8] sRM*/LVINTRO
9  <2> sassign vKS/2
a  <;> nextstate(main 4 a.pl:4) v:*,&,{,x*,x&,x$,$
b  <0> padsv[$dollarsHeld:3,8] s
c  <+> multideref($opt{"buyDollars"}) sK
d  <2> add[t7] sK/2
e  <0> padsv[$targetDollars:4,8] sRM*/LVINTRO
f  <2> sassign vKS/2
g  <;> nextstate(main 5 a.pl:5) v:*,&,{,x*,x&,x$,$
h  <0> padsv[$targetDollars:4,8] s
i  <0> padsv[$targetBasis:2,8] s
j  <2> divide[t9] sK/2
k  <0> padsv[$targetShares:5,8] sRM*/LVINTRO
l  <2> sassign vKS/2
m  <;> nextstate(main 6 a.pl:6) v:*,&,{,x*,x&,x$,$
n  <0> padsv[$targetShares:5,8] s
o  <+> multideref($s->{"held"}) sK/STRICT
p  <2> subtract[t11] sK/2
q  <0> padsv[$newShares:6,8] sRM*/LVINTRO
r  <2> sassign vKS/2
s  <;> nextstate(main 7 a.pl:7) v:*,&,{,x*,x&,x$,$
t  <+> multideref($opt{"buyDollars"}) sK
u  <0> padsv[$newShares:6,8] s
v  <2> divide[t13] sK/2
w  <0> padsv[$targetPrice:7,8] sRM*/LVINTRO
x  <2> sassign vKS/2
y  <@> leave[1 ref] vKP/REFC
a.pl syntax OK

请注意，我首先在程序中添加了以下内容:

Note that I prepended the following to the program first:

use strict;
my ($s, %opt, $targetBasis);

优化变量可以节省将值复制到变量中的过程，但是将数字标量复制到另一个变量中非常便宜.

Optimizing the variables away would save copying a value into them, but copying a numerical scalar into another one is very cheap.

我将代码保留为可读形式.可读性比节省几纳秒重要得多.

I would leave the code in its readable form. Readability is far more important than saving a few nanoseconds.

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