Trim unused interfaces

[MichalStrehovsky]

So far, the compiler could only trim unused interface methods; the interface types themselves were left alone. There is not a huge cost associated with having these extra MethodTables, but it sill impacts size/working set/startup. Initial estimate showed this could actually be up to 2% for BasicMinimalApi so I decided to investigate a fix.

This is an attempt to start trimming them. I chose a relatively conservative approach:

• Stop unconditionally rooting the interface MethodTable in the implementing class MethodTable InterfaceList. Instead check whether someone else marked it first.
• Track whether an interface type definition is used in any way. This avoids problem with variance, etc. If an interface definition is used, all instantiations that we were trying to optimize away get the MethodTable and won't be optimized. We should be able to do better than this, maybe, at some point.
• Classes that implement generic interfaces with default methods need special treatment because we index into interface list at runtime and we might not know the correct index yet. So just forget the optimization in that case.

Fixes #66716.

[filipnavara]

I vaguely remember that some part of the iOS managed static registrar or the linker pipeline may depend on the current behavior. So, cc @ivanpovazan, @simonrozsival in case they do remember the details or have some general concerns.

[simonrozsival]

@filipnavara If I understand this change correctly, I don't think this should break iOS. There are cases when we explicitly cast objects to an interface they implement and call a method on the interface. I think that falls under the second bullet point and in that case the optimization won't be applied.

[filipnavara]

I think that falls under the second bullet point and in that case the optimization won't be applied.

Thanks for checking!

[MichalStrehovsky]

/azp run runtime-nativeaot-outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[EgorBo]

ID: 100000 🎉

[MichalStrehovsky]

So this won't be quite the promised 2% size saving on WebapiAot template because once I started to worry about generic interfaces and the suppressions that assume IL level trimming we have within the libraries, it became 0.7%.

In libraries, we have several places where we call GetInterfaces() without a properly annotated/statically known type and assume that if we grab the type definition of the interface we got from GetInterfaces() and compare with typeof(OpenVersion<>), it's going to be reliable and trim safe way to detect if the type implemented say OpenVersion<int>. It's safe in IL sense. In AOT sense, we could have stripped OpenVersion<int> if it was never used and then this trim-unsafe piece of code won't find it. So we can't do it. Oh well.

But the good news is that dotnet new console --aot followed by dotnet publish /p:OptimizationPreference=Size /p:StackTraceSupport=false /p:UseSystemResourceKeys=true is now 877 kB.

Size statistics

Pull request #100000

Project	Size before	Size after	Difference
avalonia.app-linux	24681968	24615120	-66848
avalonia.app-windows	22321152	22253568	-67584
hello-linux	1316304	1266592	-49712
hello-minimal-linux	1172808	1119000	-53808
hello-minimal-windows	947200	898560	-48640
hello-windows	1200640	1149952	-50688
webapiaot-linux	10363808	10301344	-62464
webapiaot-windows	9438720	9377280	-61440

[MichalStrehovsky]

@dotnet/ilc-contrib this is ready for review

[MichalStrehovsky]

/azp run runtime-nativeaot-outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jkotas]

Nice!

[MichalStrehovsky]

Hmm, the linux-arm failure is interesting but unrelated:

(lldb) bt
This version of LLDB has no plugin for the language "assembler". Inspection of frame variables will be limited.
* thread #1, name = 'Microsoft.Exten', stop reason = signal SIGSEGV
  * frame #0: 0x00eab31e Microsoft.Extensions.Logging.Console.Tests`RhpCheckedAssignRefr1 at WriteBarriers.S:251
    frame #1: 0x011ec304 Microsoft.Extensions.Logging.Console.Tests`System.Runtime.TypeCast___cctor at TypeCast.cs:36
    frame #2: 0x0121c2b8 Microsoft.Extensions.Logging.Console.Tests`Internal.Runtime.CompilerHelpers.StartupCodeHelpers__RunInitializers(typeManager=<unavailable>, section=<unavailable>) at StartupCodeHelpers.cs:181
    frame #3: 0x0121be8e Microsoft.Extensions.Logging.Console.Tests`Internal.Runtime.CompilerHelpers.StartupCodeHelpers__InitializeModules(osModule=<unavailable>, pModuleHeaders=<unavailable>, count=<unavailable>, pClasslibFunctions=<unavailable>, nClasslibFunctions=<unavailable>) at StartupCodeHelpers.cs:53
    frame #4: 0x00e6f4d4 Microsoft.Extensions.Logging.Console.Tests`main [inlined] InitializeRuntime() at main.cpp:203:5 [opt]
    frame #5: 0x00e6f470 Microsoft.Extensions.Logging.Console.Tests`main(argc=9, argv=0xffca6804) at main.cpp:221:19 [opt]
(lldb) dis -b -A thumbv7
Microsoft.Extensions.Logging.Console.Tests`RhpCheckedAssignRef:
    0xeab2be <+0>:   0xf3bf8f5f   dmb    sy

Microsoft.Extensions.Logging.Console.Tests`RhpCheckedAssignRefr1:
    0xeab2c2 <+4>:   0x6001       str    r1, [r0]
    0xeab2c4 <+6>:   0xf2400c4c   movw   r12, #0x4c
    0xeab2c8 <+10>:  0xf2c00ca0   movt   r12, #0xa0
    0xeab2cc <+14>:  0x44fc       add    r12, pc
    0xeab2ce <+16>:  0xf8dcc000   ldr.w  r12, [r12]
    0xeab2d2 <+20>:  0x4560       cmp    r0, r12
    0xeab2d4 <+22>:  0xd328       blo    0x89b328                  ; <+106>
    0xeab2d6 <+24>:  0xf2400c3e   movw   r12, #0x3e
    0xeab2da <+28>:  0xf2c00ca0   movt   r12, #0xa0
    0xeab2de <+32>:  0x44fc       add    r12, pc
    0xeab2e0 <+34>:  0xf8dcc000   ldr.w  r12, [r12]
    0xeab2e4 <+38>:  0x4560       cmp    r0, r12
    0xeab2e6 <+40>:  0xd21f       bhs    0x89b328                  ; <+106>
    0xeab2e8 <+42>:  0xf6470ca0   movw   r12, #0x78a0
    0xeab2ec <+46>:  0xf2c00c9e   movt   r12, #0x9e
    0xeab2f0 <+50>:  0x44fc       add    r12, pc
    0xeab2f2 <+52>:  0xf8dcc000   ldr.w  r12, [r12]
    0xeab2f6 <+56>:  0x4561       cmp    r1, r12
    0xeab2f8 <+58>:  0xd31b       blo    0x89b332                  ; <+116>
    0xeab2fa <+60>:  0xf6470c92   movw   r12, #0x7892
    0xeab2fe <+64>:  0xf2c00c9e   movt   r12, #0x9e
    0xeab302 <+68>:  0x44fc       add    r12, pc
    0xeab304 <+70>:  0xf8dcc000   ldr.w  r12, [r12]
    0xeab308 <+74>:  0x4561       cmp    r1, r12
    0xeab30a <+76>:  0xd212       bhs    0x89b332                  ; <+116>
    0xeab30c <+78>:  0xf2400c00   movw   r12, #0x0
    0xeab310 <+82>:  0xf2c00c9f   movt   r12, #0x9f
    0xeab314 <+86>:  0x44fc       add    r12, pc
    0xeab316 <+88>:  0xf8dcc000   ldr.w  r12, [r12]
    0xeab31a <+92>:  0xeb0c2090   add.w  r0, r12, r0, lsr #10
->  0xeab31e <+96>:  0xf890c000   ldrb.w r12, [r0]
    0xeab322 <+100>: 0xf1bc0fff   cmp.w  r12, #0xff
    0xeab326 <+104>: 0xd100       bne    0x89b32a                  ; <+108>
    0xeab328 <+106>: 0xe003       b      0x89b332                  ; <+116>
    0xeab32a <+108>: 0xf04f0cff   mov.w  r12, #0xff
    0xeab32e <+112>: 0xf880c000   strb.w r12, [r0]
    0xeab332 <+116>: 0x4770       bx     lr
(lldb)

Cc @filipnavara

Runfo:

runfo get-helix-payload -j 320338f9-9d8c-4deb-9eeb-884cfb26892e -w Microsoft.Extensions.Logging.Console.Tests -o c:\helix_payload\Microsoft.Extensions.Logging.Console.Tests

[MichalStrehovsky]

I'll wait with merging this until after #98712. I don't want to mask off how much of a regression that PR is.

[jkotas]

the linux-arm failure is interesting

Opened #100112