C++: Add more QLDoc.

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaInternals.qll

@@ -22,6 +22,7 @@ private module SourceVariables {
 
     SourceVariable() { this = TMkSourceVariable(base, ind) }
 
+    /** Gets the IR variable associated with this `SourceVariable`, if any. */
     IRVariable getIRVariable() { result = base.(BaseIRVariable).getIRVariable() }
 
     /**

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaInternalsCommon.qll

@@ -377,6 +377,7 @@ abstract private class AbstractBaseSourceVariable extends TBaseSourceVariable {
   /** Gets the type of this base source variable. */
   final DataFlowType getType() { this.getLanguageType().hasUnspecifiedType(result, _) }
 
+  /** Gets the `CppType` of this base source variable. */
   abstract CppType getLanguageType();
 }
 

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/ssa0/SsaInternals.qll

@@ -16,6 +16,9 @@ private import semmle.code.cpp.ir.dataflow.internal.SsaInternalsCommon
 
 private module SourceVariables {
   class SourceVariable extends BaseSourceVariable {
+    /**
+     * Gets the base source variable of this `SourceVariable`.
+     */
     BaseSourceVariable getBaseVariable() { result = this }
   }
 }