Optimizer - Some progress on building UD chains

From the table of variables we build a table of per-instruction
uses/defines.

c-opopt.cc

@@ -517,6 +517,59 @@ void BUDCVisitor_(
 	}
 }
 
+/*----------------------------------------------------------------------------*/
+
+struct T_UDEntry_
+{
+	uint32_t entry;
+	bool isUse;
+	uint32_t index;
+};
+
+using T_UDEPerInstr_ = T_KeyValueTable< uint32_t , T_AutoArray< T_UDEntry_ , 8 > >;
+
+template< uint32_t S >
+void BUDCAddEntries_(
+		T_UDEPerInstr_& out ,
+		const uint32_t mainEntry ,
+		const bool isUse ,
+		T_AutoArray< T_OptData::T_VarUDRecord , S > const& entries ) noexcept
+{
+	const auto na{ entries.size( ) };
+	for ( auto j = 0u ; j < na ; j ++ ) {
+		auto const& use{ entries[ j ] };
+		auto* rec{ out.get( use.node ) };
+		if ( !rec ) {
+			out.add( use.node , T_AutoArray< T_UDEntry_ , 8 >{ } );
+			rec = out.get( use.node );
+		}
+		assert( rec );
+		
+		auto& ne{ rec->addNew( ) };
+		ne.entry = mainEntry;
+		ne.isUse = isUse;
+		ne.index = j;
+	}
+}
+
+/*----------------------------------------------------------------------------*/
+
+struct T_VarEvt_
+{
+	enum E_VarEvt {
+		DEF , USE , KILL
+	};
+
+	uint32_t instrId;
+	E_VarEvt evt;
+	T_OptData::T_VarId var;
+
+	T_VarEvt_( uint32_t instrId , E_VarEvt evt ,
+			T_OptData::T_VarId const& var )
+		: instrId( instrId ) , evt( evt ) , var( var )
+	{ }
+};
+
 
 } // namespace <anon>
 
@@ -528,28 +581,27 @@ void T_OptData::buildUseDefineChains(
 	M_LOGSTR_( "Building use/define chains" , LL1 );
 	varUDChains.clear( );
 
-	/*
-	 * We need to locate all variable uses. For each use, we will go
-	 * backwards in the graph, until one of the following becomes true:
-	 *	- we find an instruction that sets the variable;
-	 *	- we find the initial block due to cycling back;
-	 *	- we reached the CFG_ENTER node.
-	 * In the latter case, it's an error - the variable is never set.
-	 *
-	 * FIXME: Nope, actually that won't work. We need to find (set)
-	 * instuctions, calls, and also resource initialisations as well
-	 * when visiting the tree; *then* we can associate records from
-	 * both lists.
-	 *
-	 * Note: for function arguments, most of this can be avoided by simply
-	 * looking at the call sites.
-	 */
+	// Find all definitions and uses, add them to the table
 	visitor.visit( program.root , [&]( auto& n , const bool exit ) {
 		if ( !exit ) {
 			BUDCVisitor_( program.root , *this , n );
 		}
 		return true;
 	} );
+
+	// Build a table of all variable uses/defines that were identified
+	T_UDEPerInstr_ udPerInstr;
+	auto const& udcEntries{ varUDChains.values( ) };
+	const auto n{ udcEntries.size( ) };
+	for ( auto i = 0u ; i < n ; i ++ ) {
+		auto const& r{ udcEntries[ i ] };
+		BUDCAddEntries_( udPerInstr , i , true , r.uses );
+		BUDCAddEntries_( udPerInstr , i , false , r.defines );
+	}
+
+	// For each node of the CFG graph, we need to generate a sequence that
+	// indicates what gets defined, used or killed.
+	T_MultiArray< T_VarEvt_ > cfgVarEvents;
 }