Bug 11560 - Compiler should constant fold .Length calls on string constants
Summary: Compiler should constant fold .Length calls on string constants
Status: RESOLVED NOT_ON_ROADMAP
Alias: None
Product: Compilers
Classification: Mono
Component: C# ()
Version: unspecified
Hardware: PC Mac OS
: Lowest enhancement
Target Milestone: ---
Assignee: Marek Safar
URL:
Depends on:
Blocks:
 
Reported: 2013-04-03 17:24 UTC by Bojan Rajkovic [MSFT]
Modified: 2013-04-04 16:48 UTC (History)
1 user (show)

Tags:
Is this bug a regression?: ---
Last known good build:

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Status:
RESOLVED NOT_ON_ROADMAP

Description Bojan Rajkovic [MSFT] 2013-04-03 17:24:54 UTC
To save the JITter some time, it'd be nice if the compiler could transform Console.WriteLine ("foo".Length); into Console.WriteLine (3);. Currently, the IL produced does a ldstr followed by a callvirt to get_Length().
Comment 1 Marek Safar 2013-04-04 03:08:56 UTC
This cannot be done by compiler because people are running they own mscorlib with they own string implementation.
Comment 2 Mikayla Hutchinson [MSFT] 2013-04-04 13:26:16 UTC
Wait, what kind of argument is that? What are the chances anyones will ever replace string.Length with an implementation that behaves differently?
Comment 3 Marek Safar 2013-04-04 13:36:09 UTC
I saw 2 different mscorlib(s) with custom string, novell bugzilla should still have it somewhere in backlog
Comment 4 Mikayla Hutchinson [MSFT] 2013-04-04 13:57:22 UTC
I'm not disputing that there might be custom string implementations, but how likely is it that their .Length would behave differently for string constants in C# source? Is that edge case (which may never happen) really important enough to prevent this optimization?
Comment 5 Marek Safar 2013-04-04 16:48:50 UTC
It's as likely as this optimisation will have any effect. If you really need this optimisation it should be done at JIT/AOT level (it could be done already I didn't check) before doing this in all compilers. Just for C# you have normal C#, expressions trees, dynamic emitter + .net csc and I could continue with F# etc