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perl - Perl optimizer question: Will the perl compiler optimize away all of these temporary variables?

问题描述

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.

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;

Thanks.

-E

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.

标签： perloptimization

解决方案

不。

以下是程序的编译版本

$ 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：

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

优化变量可以省去将一个值复制到其中的操作，但是将一个数值标量复制到另一个变量中是非常便宜的。

我会以可读的形式保留代码。可读性远比节省几纳秒更重要。

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