Fold obj.GetType to a constant

[EgorBo]

TypeTest()=>"test".GetType();

Was:

; Method X:Test():System.Type:thissubrsp,40movrcx,0xD1FFAB1E ; 'test'call System.Object:GetType():System.Type:thisnopaddrsp,40ret; Total bytes of code: 25

Now:

; Method X:Test():System.Type:thismovrax,0xD1FFAB1E ; RuntimeType frozen object representing 'System.String'ret; Total bytes of code: 11

[ghost]

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Issue Details

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TypeTest()=>"test".GetType();

Was:

; Method X:Test():System.Type:thissubrsp,40movrcx,0xD1FFAB1E ; 'test'call System.Object:GetType():System.Type:thisnopaddrsp,40ret; Total bytes of code: 25

Now:

; Method X:Test():System.Type:thismovrax,0xD1FFAB1E ; RuntimeType frozen object representing 'System.String'ret; Total bytes of code: 11

Author:	EgorBo
Assignees:	EgorBo
Labels:	area-CodeGen-coreclr
Milestone:	-

[EgorBo]

Diffs are small: https://dev.azure.com/dnceng-public/public/_build/results?buildId=294970&view=ms.vss-build-web.run-extensions-tab due to new contexts (see missing contexts values).

We already had this optimization (mostly, for value types) this just extends it a bit 🙂 (not sure I understand why so many likes on it 😆)

PTAL @dotnet/jit-contrib

[ShreyasJejurkar]

I love to see this kind of improvement where the number of instructions is going down and down and down! 😅
These little improvements here and there contribute a lot to bigger efforts! 🙌

Keep those coming...🫡🎉