Bug 33773 - Better codegen for lifted types in null operator
Summary: Better codegen for lifted types in null operator
Status: NEW
Alias: None
Product: Compilers
Classification: Mono
Component: C# ()
Version: unspecified
Hardware: PC Mac OS
: --- enhancement
Target Milestone: ---
Assignee: Marek Safar
Depends on:
Reported: 2015-09-08 08:06 UTC by Marek Safar
Modified: 2015-09-08 08:06 UTC (History)
1 user (show)

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

Notice (2018-05-24): bugzilla.xamarin.com is now in read-only mode.

Please join us on Visual Studio Developer Community and in the Xamarin and Mono organizations on GitHub to continue tracking issues. Bugzilla will remain available for reference in read-only mode. We will continue to work on open Bugzilla bugs, copy them to the new locations as needed for follow-up, and add the new items under Related Links.

Our sincere thanks to everyone who has contributed on this bug tracker over the years. Thanks also for your understanding as we make these adjustments and improvements for the future.

Please create a new report for Bug 33773 on GitHub or Developer Community if you have new information to add and do not yet see a matching new report.

If the latest results still closely match this report, you can use the original description:

  • Export the original title and description: GitHub Markdown or Developer Community HTML
  • Copy the title and description into the new report. Adjust them to be up-to-date if needed.
  • Add your new information.

In special cases on GitHub you might also want the comments: GitHub Markdown with public comments

Related Links:

Description Marek Safar 2015-09-08 08:06:58 UTC
For most left+right expressions like binary, probe, null coalescing, etc. we could generate much better IL code.


class A
	public int P { get; set; }

class X
	public static void Main ()
		A a = null;
		var m = a?.P ?? 2;

`a?.P ?? 2` lifts int P to int? and then unwraps it with branch for 2. This all can be avoided and value `2` can be directly injected instead of empty nullable type being constructed and then checked for hasValue.

This is done for value types only and it can get tricky when we have receiver of multiple null operators (e.g. a?.P?.X).