SSA: Remove empty predicates and dead code.

Author: aschackmull

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

@@ -956,8 +956,6 @@ class GlobalDef extends Definition {
 private module SsaImpl = SsaImplCommon::Make<Location, SsaInput>;
 
 private module DataFlowIntegrationInput implements SsaImpl::DataFlowIntegrationInputSig {
-  private import codeql.util.Void
-
   class Expr extends Instruction {
     Expr() {
       exists(IRBlock bb, int i |
@@ -979,14 +977,6 @@ private module DataFlowIntegrationInput implements SsaImpl::DataFlowIntegrationI
 
   predicate ssaDefHasSource(SsaImpl::WriteDefinition def) { none() }
 
-  predicate ssaDefAssigns(SsaImpl::WriteDefinition def, Expr value) { none() }
-
-  class Parameter extends Void {
-    Location getLocation() { none() }
-  }
-
-  predicate ssaDefInitializesParam(SsaImpl::WriteDefinition def, Parameter p) { none() }
-
   predicate allowFlowIntoUncertainDef(SsaImpl::UncertainWriteDefinition def) { any() }
 
   private EdgeKind getConditionalEdge(boolean branch) {

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

@@ -1029,16 +1029,6 @@ private module DataFlowIntegrationInput implements Impl::DataFlowIntegrationInpu
     def instanceof Ssa::ImplicitParameterDefinition
   }
 
-  predicate ssaDefAssigns(WriteDefinition def, Expr value) {
-    // exclude flow directly from RHS to SSA definition, as we instead want to
-    // go from RHS to matching assingnable definition, and from there to SSA definition
-    none()
-  }
-
-  class Parameter = Ssa::ImplicitParameterDefinition;
-
-  predicate ssaDefInitializesParam(WriteDefinition def, Parameter p) { none() }
-
   /**
    * Allows for flow into uncertain defintions that are not call definitions,
    * as we, conservatively, consider such definitions to be certain.

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

@@ -647,16 +647,10 @@ private module DataFlowIntegrationInput implements Impl::DataFlowIntegrationInpu
 
   Expr getARead(Definition def) { result = getAUse(def) }
 
-  class Parameter = J::Parameter;
-
   predicate ssaDefHasSource(WriteDefinition def) {
     def instanceof SsaExplicitUpdate or def.(SsaImplicitInit).isParameterDefinition(_)
   }
 
-  predicate ssaDefAssigns(Impl::WriteDefinition def, Expr value) { none() }
-
-  predicate ssaDefInitializesParam(Impl::WriteDefinition def, Parameter p) { none() }
-
   predicate allowFlowIntoUncertainDef(UncertainWriteDefinition def) {
     def instanceof SsaUncertainImplicitUpdate
   }

javascript/ql/lib/semmle/javascript/dataflow/internal/sharedlib/Ssa.qll

@@ -61,18 +61,6 @@ module SsaDataflowInput implements DataFlowIntegrationInputSig {
     none()
   }
 
-  predicate ssaDefAssigns(WriteDefinition def, Expr value) {
-    // This library only handles use-use flow after a post-update, there are no definitions, only uses.
-    none()
-  }
-
-  class Parameter = js::Parameter;
-
-  predicate ssaDefInitializesParam(WriteDefinition def, Parameter p) {
-    // This library only handles use-use flow after a post-update, there are no definitions, only uses.
-    none()
-  }
-
   cached
   Expr getARead(Definition def) {
     // Copied from implementation so we can cache it here

ruby/ql/lib/codeql/ruby/dataflow/internal/SsaImpl.qll

@@ -473,18 +473,12 @@ class ParameterExt extends TParameterExt {
 private module DataFlowIntegrationInput implements Impl::DataFlowIntegrationInputSig {
   private import codeql.ruby.controlflow.internal.Guards as Guards
 
-  class Parameter = ParameterExt;
-
   class Expr extends Cfg::CfgNodes::ExprCfgNode {
     predicate hasCfgNode(SsaInput::BasicBlock bb, int i) { this = bb.getNode(i) }
   }
 
   Expr getARead(Definition def) { result = Cached::getARead(def) }
 
-  predicate ssaDefAssigns(WriteDefinition def, Expr value) { none() }
-
-  predicate ssaDefInitializesParam(WriteDefinition def, Parameter p) { none() }
-
   class Guard extends Cfg::CfgNodes::AstCfgNode {
     /**
      * Holds if the control flow branching from `bb1` is dependent on this guard,

rust/ql/lib/codeql/rust/dataflow/internal/SsaImpl.qll

@@ -342,11 +342,6 @@ private module DataFlowIntegrationInput implements Impl::DataFlowIntegrationInpu
 
   predicate ssaDefHasSource(WriteDefinition def) { none() } // handled in `DataFlowImpl.qll` instead
 
-  /** Holds if SSA definition `def` assigns `value` to the underlying variable. */
-  predicate ssaDefAssigns(WriteDefinition def, Expr value) {
-    none() // handled in `DataFlowImpl.qll` instead
-  }
-
   private predicate isArg(CfgNodes::CallExprBaseCfgNode call, CfgNodes::ExprCfgNode e) {
     call.getArgument(_) = e
     or
@@ -366,13 +361,6 @@ private module DataFlowIntegrationInput implements Impl::DataFlowIntegrationInpu
     )
   }
 
-  class Parameter = CfgNodes::ParamBaseCfgNode;
-
-  /** Holds if SSA definition `def` initializes parameter `p` at function entry. */
-  predicate ssaDefInitializesParam(WriteDefinition def, Parameter p) {
-    none() // handled in `DataFlowImpl.qll` instead
-  }
-
   class Guard extends CfgNodes::AstCfgNode {
     /**
      * Holds if the control flow branching from `bb1` is dependent on this guard,

shared/ssa/codeql/ssa/Ssa.qll

@@ -1468,21 +1468,6 @@ module Make<LocationSig Location, InputSig<Location> Input> {
      */
     default predicate ssaDefHasSource(WriteDefinition def) { any() }
 
-    /** Holds if SSA definition `def` assigns `value` to the underlying variable. */
-    predicate ssaDefAssigns(WriteDefinition def, Expr value);
-
-    /** A parameter. */
-    class Parameter {
-      /** Gets a textual representation of this parameter. */
-      string toString();
-
-      /** Gets the location of this parameter. */
-      Location getLocation();
-    }
-
-    /** Holds if SSA definition `def` initializes parameter `p` at function entry. */
-    predicate ssaDefInitializesParam(WriteDefinition def, Parameter p);
-
     /**
      * Holds if flow should be allowed into uncertain SSA definition `def` from
      * previous definitions or reads.
@@ -1675,17 +1660,7 @@ module Make<LocationSig Location, InputSig<Location> Input> {
     cached
     private newtype TNode =
       TWriteDefSource(WriteDefinition def) { DfInput::ssaDefHasSource(def) } or
-      TParamNode(DfInput::Parameter p) {
-        exists(WriteDefinition def | DfInput::ssaDefInitializesParam(def, p))
-      } or
-      TExprNode(DfInput::Expr e, Boolean isPost) {
-        e = DfInput::getARead(_)
-        or
-        exists(DefinitionExt def |
-          DfInput::ssaDefAssigns(def, e) and
-          isPost = false
-        )
-      } or
+      TExprNode(DfInput::Expr e, Boolean isPost) { e = DfInput::getARead(_) } or
       TSsaDefinitionNode(DefinitionExt def) { not phiHasUniqNextNode(def) } or
       TSsaInputNode(SsaPhiExt phi, BasicBlock input) { relevantPhiInputNode(phi, input) }
 
@@ -1722,22 +1697,6 @@ module Make<LocationSig Location, InputSig<Location> Input> {
 
     final class WriteDefSourceNode = WriteDefSourceNodeImpl;
 
-    /** A parameter node. */
-    private class ParameterNodeImpl extends NodeImpl, TParamNode {
-      private DfInput::Parameter p;
-
-      ParameterNodeImpl() { this = TParamNode(p) }
-
-      /** Gets the underlying parameter. */
-      DfInput::Parameter getParameter() { result = p }
-
-      override string toString() { result = p.toString() }
-
-      override Location getLocation() { result = p.getLocation() }
-    }
-
-    final class ParameterNode = ParameterNodeImpl;
-
     /** A (post-update) expression node. */
     abstract private class ExprNodePreOrPostImpl extends NodeImpl, TExprNode {
       DfInput::Expr e;
@@ -2003,14 +1962,7 @@ module Make<LocationSig Location, InputSig<Location> Input> {
     predicate localFlowStep(SourceVariable v, Node nodeFrom, Node nodeTo, boolean isUseStep) {
       exists(Definition def |
         // Flow from write definition source into SSA definition
-        nodeFrom = TWriteDefSource(def)
-        or
-        // Flow from assignment into SSA definition
-        DfInput::ssaDefAssigns(def, nodeFrom.(ExprNode).getExpr())
-        or
-        // Flow from parameter into entry definition
-        DfInput::ssaDefInitializesParam(def, nodeFrom.(ParameterNode).getParameter())
-      |
+        nodeFrom = TWriteDefSource(def) and
         isUseStep = false and
         if DfInput::includeWriteDefsInFlowStep()
         then
@@ -2042,14 +1994,7 @@ module Make<LocationSig Location, InputSig<Location> Input> {
     predicate localMustFlowStep(SourceVariable v, Node nodeFrom, Node nodeTo) {
       exists(Definition def |
         // Flow from write definition source into SSA definition
-        nodeFrom = TWriteDefSource(def)
-        or
-        // Flow from assignment into SSA definition
-        DfInput::ssaDefAssigns(def, nodeFrom.(ExprNode).getExpr())
-        or
-        // Flow from parameter into entry definition
-        DfInput::ssaDefInitializesParam(def, nodeFrom.(ParameterNode).getParameter())
-      |
+        nodeFrom = TWriteDefSource(def) and
         v = def.getSourceVariable() and
         if DfInput::includeWriteDefsInFlowStep()
         then nodeTo.(SsaDefinitionNode).getDefinition() = def