Call Enter/LeaveRegion APIs for binary expressions

[RikkiGibson]

Closes #38087

[RikkiGibson]

We don't call 'VisitAlways' on the binary nodes themselves to avoid recursion. Therefore we need to take care to call Enter/LeaveRegion APIs appropriately when we start/finish with those nodes.

See also #74317 for a non-recursive visitor which makes similar calls.

[CyrusNajmabadi]

Thanks. I can also hellp with adding an ExtractMethod test if you need it.

[RikkiGibson]

We need to take care that Enter is called for all the binary ops, from outermost to innermost, and then Leave is called from innermost to outermost. Most convenient way to do this is to call Enter right after Push, then Leave right before "Pop or exit".

[RikkiGibson]

@CyrusNajmabadi If you have some time feel free to push an ExtractMethod test to this PR.

[RikkiGibson]

@dotnet/roslyn-compiler for review of a small fix

[AlekseyTs]

Does VB have the same issue?

[RikkiGibson]

VB implementation appears to be accounting for this when visiting binary expressions.

roslyn/src/Compilers/VisualBasic/Portable/Analysis/FlowAnalysis/AbstractFlowPass.vb

Lines 2135 to 2160 in fe3a243

	' As we emulate visiting, enter the region if needed.
	' We shouldn't do this for the top most node,
	' VisitBinaryOperator caller such as VisitRvalue(...) does this.
	If Me._regionPlace = RegionPlace.Before Then
	If stack.Count > 0 Then
	' Skipping the first node
	Debug.Assert(stack(0) Is node)
	For i As Integer = 1 To stack.Count - 1
	If stack(i) Is Me._firstInRegion Then
	Me.EnterRegion()
	GoTo EnteredRegion
	End If
	Next
	' Note, the last binary operator is not pushed to the stack, it is stored in [binary].
	Debug.Assert(binary IsNot node)
	If binary Is Me._firstInRegion Then
	Me.EnterRegion()
	End If
	EnteredRegion:
	Else
	Debug.Assert(binary Is node)
	End If
	End If

But, at a glance, I didn't find a test in RegionAnalysisTests.vb which is doing a dataflow analysis on a nested binary operator.

[AlekseyTs]

Consider adding a test

[AlekseyTs]

Done with review pass (commit 7)

[AlekseyTs]

LGTM (commit 8)