Updating lclmorph to support bitcast

[tannergooding]

With #71567, the front end now has minimal support for GT_BITCAST nodes including value numbering and constant folding.

It should now be feasible to address some of the TODO-ADDR comments in LocalAddressVisitor::SelectLocalIndirTransform and LocalAddressVisitor::MorphLocalAddress by recognizing certain indirections as being representable as a GT_BITCAST rather than keeping it as a GT_IND.

To start we should likely only handle float<->int/uint and double<->long/ulong. There may also be some benefit in handling conversions surrounding simd8.

In the future this could likely be extended to struct types and potentially other primitives as well.

category:cq
theme:morph

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Issue Details

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With #71567, the front end now has minimal support for GT_BITCAST nodes including value numbering and constant folding.

It should now be feasible to address some of the TODO-ADDR comments in LocalAddressVisitor::SelectLocalIndirTransform and LocalAddressVisitor::MorphLocalAddress by recognizing certain indirections as being representable as a GT_BITCAST rather than keeping it as a GT_IND.

To start we should likely only handle float<->int/uint and double<->long/ulong. There may also be some benefit in handling conversions surrounding simd8.

In the future this could likely be extended to struct types and potentially other primitives as well.

Author:	tannergooding
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[JulieLeeMSFT]

cc @dotnet/jit-contrib.

[AndyAyersMS]

@tannergooding is this something you hope to see in .net 8?

[SingleAccretion]

This is now effectively a one-line change:

runtime/src/coreclr/jit/lclmorph.cpp

Lines 1027 to 1035 in fb001c4

	// Turn this into a bitcast if we can.
	if ((genTypeSize(indir) == genTypeSize(varDsc)) && (varTypeIsFloating(indir) || varTypeIsFloating(varDsc)))
	{
	// TODO-ADDR: enable this optimization for all users and all targets.
	if (user->OperIs(GT_RETURN) && (genTypeSize(indir) <= TARGET_POINTER_SIZE))
	{
	return IndirTransform::BitCast;
	}
	}

[TIHan]

@SingleAccretion you still working on this one?

[SingleAccretion]

Yes, if not "right now". If someone wants to do the (small) amount of work to close this issue though, they should feel free to do so.