Use StrongBox<Rect> over object field in GlyphRun

[h3xds1nz]

Description

Swaps an object field with StrongBox<Rect> when caching ink bounds to allow for faster unboxing when required and increase type-safety in the codebase. Given that caching is present on most codepaths, this could theoretically be better nowadays to embed the Rect directly into GlyphRun, but that requires more measurements.

In StrongBox, we just load the field:

   mov       rax,[rsi+8]
   test      rax,rax
   je        short M01_L00
   vmovdqu   ymm1,ymmword ptr [rax+8]
   vmovdqu   ymmword ptr [rbx],ymm1
   mov       rax,rbx

With object, we have to go through type-check etc:

     mov       rdi,[rsi+8]
     test      rdi,rdi
     je        short M01_L01
     mov       rcx,offset MT_System.Windows.Rect
     cmp       [rdi],rcx
     je        short M01_L00
     mov       rdx,rdi
     call      System.Runtime.CompilerServices.CastHelpers.Unbox(Void*, System.Object)
M01_L00:
     vmovdqu   ymm1,ymmword ptr [rdi+8]
     vmovdqu   ymmword ptr [rbx],ymm1
     mov       rax,rbx

With 1 box, 100 returns, this gets down to:

Method	Mean [ns]	Error [ns]	StdDev [ns]	Code Size [B]	Gen0	Allocated [B]
Original	196.4 ns	1.71 ns	1.60 ns	424 B	0.0048	80 B
PR__EDIT	174.3 ns	1.48 ns	1.32 ns	395 B	0.0048	80 B

Customer Impact

Increased performance, increased type safety and cleaner code.

Regression

No.

Testing

Local build.

Risk

Low.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 2.98859%. Comparing base (57fe8ac) to head (ef5c944).
Report is 10 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main     #10879          +/-   ##
===================================================
- Coverage   13.48885%   2.98859%   -10.50026%     
===================================================
  Files           3317       3319           +2     
  Lines         664749     664895         +146     
  Branches       74643      74675          +32     
===================================================
- Hits           89667      19871       -69796     
- Misses        572488     644844       +72356     
+ Partials        2594        180        -2414     

Flag	Coverage Δ
Debug	2.98859% <0.00000%> (-10.50026%)	⬇️

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