Update var life for multireg local

[CarolEidt]

When a multi-reg var is defined by a call, but doesn't currently reside in a register,
we must still update liveness.

Fix #21500

[CarolEidt]

@dotnet/jit-contrib PTAL

[CarolEidt]

test OSX10.12 x64 Checked Innerloop Build and Test
test Ubuntu x64 Checked CoreFX Tests
test Windows_NT arm Cross Checked Innerloop Build and Test

[sandreenko]

@CarolEidt could you please explain the general rule that we use to decide were we need to call genUpdateLife for stack location?

Looking at codegenarm64.cpp I see different cases:
genCodeForStoreLclVar updates for both cases;

genLockedInstructions updates only for registers, is it another missed case that we do not have a repro for or we need an assert that reg != REG_NA?

coreclr/src/jit/codegenarm64.cpp

Lines 2717 to 2722 in bbfafe7

	if (treeNode->gtRegNum != REG_NA)
	{
	genProduceReg(treeNode);
	}
	}

The same for genCodeForStoreLclVar, genCodeForCompare,.

[CarolEidt]

could you please explain the general rule that we use to decide were we need to call genUpdateLife for stack location?

It needs to be called whenever the node is a tracked lclVar. Note that genProduceReg, in addition to updating liveness (in the lclVar case), also takes care of any necessary reload from spill (in the more general case).

[sandreenko]

It needs to be called whenever the node is a tracked lclVar. Note that genProduceReg, in addition to updating liveness (in the lclVar case), also takes care of any necessary reload from spill (in the more general case).

So do we need to call it in genLockedInstructions, genCodeForStoreLclVar, and genCodeForCompare?

[CarolEidt]

So do we need to call it in genLockedInstructions, genCodeForStoreLclVar, and genCodeForCompare?

It is already being called in genCodeForeStoreLclVar for the non-multireg-call case here: https://github.com/dotnet/coreclr/blob/master/src/jit/codegenarm64.cpp#L1759

It doesn't need to be called for the other two you mention because they are not lclVars. They may consume lclVars, in which case the genConsumeReg will take care of the liveness (note that on arm and arm64 we don't have contained nodes so we don't need to worry about taking care of liveness for a non-reg operand).

[sandreenko]

LGTM, thank you.