C#: Instantiate shared SSA wrappers.

Author: aschackmull

csharp/ql/lib/semmle/code/csharp/dataflow/SSA.qll

@@ -3,13 +3,15 @@
  */
 
 import csharp
+private import internal.SsaImpl as SsaImpl
+import SsaImpl::Ssa_
 
 /**
  * Provides classes for working with static single assignment (SSA) form.
  */
 module Ssa {
-  private import internal.SsaImpl as SsaImpl
   private import semmle.code.csharp.internal.Location
+  import SsaImpl::Ssa_
 
   pragma[nomagic]
   private predicate assignableDefinitionLocalScopeVariable(

csharp/ql/lib/semmle/code/csharp/dataflow/internal/BaseSSA.qll

@@ -1,9 +1,20 @@
-import csharp
+private import csharp as CS
 
 /**
  * Provides a simple SSA implementation for local scope variables.
  */
 module BaseSsa {
+  private import BaseSsaImpl
+
+  class SimpleLocalScopeVariable = BaseSsaImpl::SimpleLocalScopeVariable;
+
+  module Ssa = SsaImpl::MakeSsa<SsaInput>;
+
+  import Ssa
+}
+
+private module BaseSsaImpl {
+  private import CS
   private import AssignableDefinitions
   private import codeql.ssa.Ssa as SsaImplCommon
 
@@ -13,7 +24,7 @@ module BaseSsa {
     predicate ref() { any() }
 
     cached
-    predicate backref() { (exists(any(SsaDefinition def).getARead()) implies any()) }
+    predicate backref() { (exists(any(BaseSsa::SsaDefinition def).getARead()) implies any()) }
   }
 
   /**
@@ -112,11 +123,9 @@ module BaseSsa {
     }
   }
 
-  private module SsaImpl = SsaImplCommon::Make<Location, Cfg, SsaImplInput>;
-
-  private module SsaInput implements SsaImpl::SsaInputSig {
-    private import csharp as CS
+  module SsaImpl = SsaImplCommon::Make<Location, Cfg, SsaImplInput>;
 
+  module SsaInput implements SsaImpl::SsaInputSig {
     class Expr = CS::Expr;
 
     class Parameter = CS::Parameter;
@@ -139,8 +148,4 @@ module BaseSsa {
       w.isParameterInit(v)
     }
   }
-
-  module Ssa = SsaImpl::MakeSsa<SsaInput>;
-
-  import Ssa
 }

csharp/ql/lib/semmle/code/csharp/dataflow/internal/SsaImpl.qll

@@ -42,6 +42,39 @@ private module SsaImplInput implements SsaImplCommon::InputSig<Location, BasicBl
 
 import SsaImplCommon::Make<Location, Cfg, SsaImplInput> as Impl
 
+private module SsaInput implements Impl::SsaInputSig {
+  private import csharp as CS
+
+  class Expr = CS::Expr;
+
+  class Parameter = CS::Parameter;
+
+  class VariableWrite extends AssignableDefinition {
+    Expr asExpr() { result = this.getExpr() }
+
+    Expr getValue() { result = this.getSource() }
+
+    predicate isParameterInit(Parameter p) { this.(ImplicitParameterDefinition).getParameter() = p }
+  }
+
+  predicate explicitWrite(VariableWrite w, BasicBlock bb, int i, SsaImplInput::SourceVariable v) {
+    exists(AssignableDefinition ad | variableDefinition(bb, i, v, ad) |
+      w = ad or
+      w = getASameOutRefDefAfter(v, ad)
+    )
+    or
+    exists(Parameter p |
+      implicitEntryDefinition(bb, v) and
+      i = -1 and
+      p = v.getAssignable() and
+      pragma[only_bind_out](p.getCallable()) = pragma[only_bind_out](v.getEnclosingCallable()) and
+      w.isParameterInit(p)
+    )
+  }
+}
+
+module Ssa_ = Impl::MakeSsa<SsaInput>;
+
 class Definition = Impl::Definition;
 
 class WriteDefinition = Impl::WriteDefinition;