Improve FMA code generation related to operand last use

[weilinwa]

In current xarch FMA code generation, last use information of operands are used to guide the form selection. There are spaces left to improve the usage of this info. Please refer to the comment here.

Another issue to solve is the last use info change in between lowering phase and lsra phase cause some assert failure in lsra phase here.

category:cq
theme:codegen
skill-level:expert
cost:medium
impact:medium

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Issue Details

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In current xarch FMA code generation, last use information of operands are used to guide the form selection. There are spaces left to improve the usage of this info. Please refer to the comment here.

Another issue to solve is the last use info change in between lowering phase and lsra phase cause some assert failure in lsra phase here.

Author:	weilinwa
Assignees:	-
Labels:	area-CodeGen-coreclr, untriaged
Milestone:	-

[JulieLeeMSFT]

CC @kunalspathak @dotnet/jit-contrib.

[JulieLeeMSFT]

Moved to .NET 8 becaue .NET 7 code complete is getting close.