Generates a UWOP_PUSH_NONVOL unwind code entry for the specified register number using the current offset in the prologue.
.PUSHREG allows ml64.exe users to specify how a frame function unwinds, and is only allowed within the prologue, which extends from the PROC FRAME declaration to the .ENDPROLOG directive. These directives do not generate code; they only generate .xdata and .pdata. .PUSHREG should be preceded by instructions that actually implement the actions to be unwound. It is a good practice to wrap both the unwind directives and the code they are meant to unwind in a macro to ensure agreement.
For more information, see MASM for x64 (ml64.exe).