OpenAD - XAIF for toy problem

The XAIF representation for the toy problem
        subroutine head(x,y) 
double precision,intent(in) :: x
double precision,intent(out) :: y
y=sin(x*x)
end subroutine
is given below with colored sections for the assignment statement and front-end generated pseudo-registers and markers that are not subject to the transformation process. All other elements have the role indicated by their respective XML element names.
<?xml version="1.0" encoding="UTF-8"?>

<!-- ******************************************************************** -->
<!-- XAIF file translated from WHIRL at Mon Sep 13 03:47:55 2004 -->
<!-- ******************************************************************** -->

<xaif:CallGraph xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xaif="http://www.mcs.anl.gov/XAIF" xsi:schemaLocation="http://www.mcs.anl.gov/XAIF xaif.xsd" program_name="***myprog***" prefix="OpenAD_">
<xaif:ScopeHierarchy>
<xaif:Scope vertex_id="1" annotation="{SymTab_Id#1}">
<xaif:SymbolTable>
<xaif:Symbol symbol_id=".preg_B_1" kind="variable" type="integer" shape="scalar" annotation="{Sym_Id#1}" active="0"/>
<xaif:Symbol symbol_id=".preg_I4_2" kind="variable" type="integer" shape="scalar" annotation="{Sym_Id#2}" active="0"/>
<xaif:Symbol symbol_id=".preg_I8_3" kind="variable" type="integer" shape="scalar" annotation="{Sym_Id#3}" active="0"/>
<xaif:Symbol symbol_id=".preg_U4_4" kind="variable" type="integer" shape="scalar" annotation="{Sym_Id#4}" active="0"/>
<xaif:Symbol symbol_id=".preg_U8_5" kind="variable" type="integer" shape="scalar" annotation="{Sym_Id#5}" active="0"/>
<xaif:Symbol symbol_id=".preg_F4_6" kind="variable" type="real" shape="scalar" annotation="{Sym_Id#6}" active="0"/>
<xaif:Symbol symbol_id=".preg_F8_7" kind="variable" type="real" shape="scalar" annotation="{Sym_Id#7}" active="0"/>
<xaif:Symbol symbol_id=".preg_F10_8" kind="variable" type="real" shape="scalar" annotation="{Sym_Id#8}" active="0"/>
<xaif:Symbol symbol_id=".preg_F16_9" kind="variable" type="real" shape="scalar" annotation="{Sym_Id#9}" active="0"/>
<xaif:Symbol symbol_id=".preg_FQ_10" kind="variable" type="real" shape="scalar" annotation="{Sym_Id#10}" active="0"/>
<xaif:Symbol symbol_id=".preg_C4_11" kind="variable" type="complex" shape="scalar" annotation="{Sym_Id#11}" active="0"/>
<xaif:Symbol symbol_id=".preg_C8_12" kind="variable" type="complex" shape="scalar" annotation="{Sym_Id#12}" active="0"/>
<xaif:Symbol symbol_id=".preg_CQ_13" kind="variable" type="complex" shape="scalar" annotation="{Sym_Id#13}" active="0"/>
<xaif:Symbol symbol_id=".preg_C10_15" kind="variable" type="complex" shape="scalar" annotation="{Sym_Id#15}" active="0"/>
<xaif:Symbol symbol_id=".preg_C16_16" kind="variable" type="complex" shape="scalar" annotation="{Sym_Id#16}" active="0"/>
<xaif:Symbol symbol_id=".preg_I16_17" kind="variable" type="integer" shape="scalar" annotation="{Sym_Id#17}" active="0"/>
<xaif:Symbol symbol_id=".preg_U16_18" kind="variable" type="integer" shape="scalar" annotation="{Sym_Id#18}" active="0"/>
<xaif:Symbol symbol_id="head__20" kind="subroutine" type="void" annotation="{Sym_Id#20}"/>
<xaif:Symbol symbol_id="SIN_21" kind="subroutine" type="void" annotation="{Sym_Id#21}"/>
</xaif:SymbolTable>
</xaif:Scope>

<xaif:Scope vertex_id="2" annotation="{SymTab_Id#2}">
<xaif:SymbolTable>
<xaif:Symbol symbol_id="X_1" kind="variable" type="real" shape="scalar" annotation="{Sym_Id#1}" active="1"/>
<xaif:Symbol symbol_id="Y_2" kind="variable" type="real" shape="scalar" annotation="{Sym_Id#2}" active="1"/>
</xaif:SymbolTable>
</xaif:Scope>

<xaif:ScopeEdge edge_id="1" source="2" target="1"/>

</xaif:ScopeHierarchy>

<!-- ******************************************************************** -->
<xaif:ControlFlowGraph vertex_id="1" scope_id="1" symbol_id="head__20" annotation="{PU_Id#1}" controlflowgraph_scope_id="2">
<xaif:ArgumentList>
<xaif:ArgumentSymbolReference position="1" scope_id="2" symbol_id="X_1" intent="in" annotation="{WHIRL_Id#2}"/>
<xaif:ArgumentSymbolReference position="2" scope_id="2" symbol_id="Y_2" intent="out" annotation="{WHIRL_Id#3}"/>
</xaif:ArgumentList>

<xaif:Entry vertex_id="1" annotation="{WHIRL_Id#}"/>

<xaif:BasicBlock vertex_id="2" scope_id="2" annotation="{WHIRL_Id#7:8:14}">
<xaif:Marker statement_id="7" annotation="{WHIRL_Id#7} [passive: OPR_PRAGMA]"/>
<xaif:Assignment statement_id="8">
<xaif:AssignmentLHS du_ud="2">
<xaif:SymbolReference vertex_id="1" scope_id="2" symbol_id="Y_2"/>
</xaif:AssignmentLHS>
<xaif:AssignmentRHS>
<xaif:Intrinsic vertex_id="1" name="sin_scal" type="***" annotation="{IntrinsicKey#0_SIN}"/>
<xaif:Intrinsic vertex_id="2" name="mul_scal_scal" type="***"/>
<xaif:VariableReference vertex_id="3" du_ud="1">
<xaif:SymbolReference vertex_id="1" scope_id="2" symbol_id="X_1"/>
</xaif:VariableReference>
<xaif:VariableReference vertex_id="4" du_ud="1">
<xaif:SymbolReference vertex_id="1" scope_id="2" symbol_id="X_1"/>
</xaif:VariableReference>
<xaif:ExpressionEdge edge_id="1" source="3" target="2" position="1"/>
<xaif:ExpressionEdge edge_id="2" source="4" target="2" position="2"/>
<xaif:ExpressionEdge edge_id="3" source="2" target="1" position="1"/>
</xaif:AssignmentRHS>
</xaif:Assignment>
<xaif:Marker statement_id="14" annotation="{WHIRL_Id#14} [passive: OPR_RETURN]"/>
</xaif:BasicBlock>

<xaif:Exit vertex_id="3" annotation="{WHIRL_Id#}"/>

<xaif:ControlFlowEdge edge_id="1" source="1" target="2"/>
<xaif:ControlFlowEdge edge_id="2" source="2" target="3"/>
</xaif:ControlFlowGraph>

</xaif:CallGraph>