Debug VM assert in DoubleToFloatInstr::Canonicalize

[fuzzybinary]

I build Dart from source to use it as an embedding scripting language and I've come across a weird assertion. After running my code for a few seconds, the compiler asserts with the following message:

../../runtime/vm/compiler/backend/il.cc: 2214: error: expected: use->instruction()->IsPhi() || use->instruction()->IsFloatToDouble() || (use->instruction()->IsStoreIndexed() && (use->instruction()->AsStoreIndexed()->class_id() == kTypedDataFloat32ArrayCid))

It appears the instruction failing the use assertion is a MaterializeObjectInstr instruction (see screenshot here):
https://twitter.com/fuzzybinary/status/1377418669567791104?s=20

I was asked to provide a dump from FlowGraphPrinter, which is here:
https://gist.github.com/fuzzybinary/2a6f82d9a358c886356e3de53eb1caa5

This is building Dart from the current 2.12.2 label on Windows

[gmpassos]

Can you test it at Linux too? Just to confirm if happens in other platforms.

[gmpassos]

The called method with the assertion error:
https://github.com/dart-lang/sdk/blob/master/runtime/vm/compiler/backend/il.cc#L2239

[fuzzybinary]

Can you test it at Linux too? Just to confirm if happens in other platforms.

Unfortunately not easily. I can maybe try to get my MacOS build running but it might take a few days.

It looks like the assertion is likely caused by this line in the FlowGraph:

 v1597 <- MaterializeObject(_Float32List, :array_element: v586, :array_element: v578, :array_element: v570) T{*?}

Which I think relates to this line in the provided code:

var tracking = Vector3(diff.x * parallax.trackCamera.x, diff.y * parallax.trackCamera.y, 0.0);

I can potentially try to reproduce using that code only, but I'm not entirely sure what's causing the recompile? Is it attempting to optimize a hotspot after several iterations?

[mraleph]

Related to recently implemented allocation sinking of the arrays. Probably benign (assertion just needs an adjustment) but we should check that we materialize correct array on deopt

[fuzzybinary]

For what it's worth, since I'm building from source I commented out the assertion for now and I'm not seeing any adverse effects.

[gmpassos]

Try a Linux VM with Virtual Box. I do this in my mac to test some code with Linux.

[fuzzybinary]

Try a Linux VM with Virtual Box. I do this in my mac to test some code with Linux.

My embedding use case is as a scripting language for a homegrown game engine. Reproducing in Linux would require porting the engine 😁

[alexmarkov]

In addition to an overly strict assertion, there was a bug in materialization of Float32List elements in case of deoptimization.
The bug is not platform-specific and may appear on any OS/CPU.

Fix: https://dart-review.googlesource.com/c/sdk/+/193831.