.NET 9, Android: AOT compiler currently fails with an assertion

[jonathanpeppers]

Description

This started happening in our PR moving to .NET 9:

dotnet/android#8366

dotnet build -c Release fails with:

Microsoft.Android.Sdk.Aot.targets(109,5): Precompiling failed for obj\Release\android-arm64\linked\Java.Interop.dll with exit code 57005.
Mono Ahead of Time compiler - compiling assembly C:\a\_work\1\a\TestRelease\11-15_21.06.00\temp\BasicProjectTrue\obj\Release\android-arm64\linked\Java.Interop.dll
AOTID AF248EDF-40DF-6D3F-1C1A-A37FAD329420
Using profile data file 'C:\a\_work\1\s\bin\Release\dotnet\packs\Microsoft.Android.Sdk.Windows\34.99.0-ci.darc-main-583d6f71-0641-4428-9c9f-b64ebed2e33e.85\targets\dotnet.aotprofile'
Added 167 methods from profile.
* Assertion at D:\a\_work\1\s\src\mono\mono\mini\mini-arm64.c:673, condition `imms >= 0 && imms < 128' not met 

Reproduction Steps

1. dotnet new android
2. dotnet build -c Release

Expected behavior

No build error

Actual behavior

Build error with assertion in mini-arm64.c

Regression?

Yes

Known Workarounds

You could disable the AOT compiler with RunAOTCompilation=false.

Configuration

.NET SDK: 9.0.100-alpha.1.23563.1
Runtime: 9.0.0-alpha.1.23557.14

Other information

Binlog: net9aot.zip

I tried updating the AOT profile, just to see if it would help: dotnet/android@2bf05c3

But I get the same issue, still.

[jonathanpeppers]

/cc @steveisok

[steveisok]

@vargaz can you look into this?

[vargaz]

Seems to be caused by:
#93606

[steveisok]

/cc @SamMonoRT

[vargaz]

Can't test it, but the problem might be in the definition of mono_lzcnt32/mono_lzcnt64 on windows:

int mono_lzcnt32 (guint32 x)
{
#ifdef _MSC_VER
	unsigned long index = 0;
	if ( _BitScanReverse( &index, x ) )
		return (int)index;
	else
		return 32;
#else
	return __builtin_clz(x);
#endif
}

For 12, __builtin_clz () returns 28, while according to msdn, _BitScanReverse () returns 3:
https://learn.microsoft.com/en-us/cpp/intrinsics/bitscanreverse-bitscanreverse64?view=msvc-170

because _BitScanReverse () returns the bit position of the highest bit set, and clz returns the number of leading zeroes.

[vargaz]

#94901

[vargaz]

Could you bump the version in the PR to see if #94901 fixes it ?

[jonathanpeppers]

It looks like the dotnet/runtime in dotnet/installer is about 3 weeks old.

For now, I tried moving ahead to get the latest runtime: dotnet/android@5702a63

[jonathanpeppers]

It took a little work to get the right runtime bits installed, but this appears to be fixed now.

We still have some test failures, but all of the AOT failures before look to be gone. Thanks!