Copy propagation needs to propagate variables, not values

[SingleAccretion]

Copy propagation today can substitute uses with live defs of locals. In doing so, it compares the value number of the def to the value of the use as a LCL_VAR. This is not correct because of zero-offset field sequences. Consider:

var a1 = addr; // Zero [FldSeq]
var a2 = addr; // No FldSeq

use LCL_VAR a2 Zero [FldSeq] // Attached to the node itself

If we replace the use with a1, then on renumbering (under JitOptRepeat) we will have a duplicated sequence.

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Issue Details

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Copy propagation today can substitute uses with live defs of locals. In doing so, it compares the value number of the local's def to the value of the use as a LCL_VAR. This is not correct because of zero-offset field sequences. Consider:

var a1 = addr; // Zero [FldSeq]
var a2 = addr; // No FldSeq

use LCL_VAR a2 Zero [FldSeq] // Attached to the node itself

If we replace the use with a1, then on renumbering (under JitOptRepeat) we will have a duplicated sequence.

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