SSA: Remove the need for ExitBasicBlock in SSA.

Author: aschackmull

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

@@ -769,8 +769,4 @@ module InputSigCommon {
   BasicBlock getImmediateBasicBlockDominator(BasicBlock bb) { result.immediatelyDominates(bb) }
 
   BasicBlock getABasicBlockSuccessor(BasicBlock bb) { result = bb.getASuccessor() }
-
-  class ExitBasicBlock extends BasicBlock {
-    ExitBasicBlock() { this.getLastInstruction() instanceof ExitFunctionInstruction }
-  }
 }

csharp/ql/lib/semmle/code/csharp/controlflow/internal/PreSsa.qll

@@ -90,7 +90,7 @@ module PreSsa {
 
     BasicBlock getABasicBlockSuccessor(BasicBlock bb) { result = bb.getASuccessor() }
 
-    class ExitBasicBlock extends BasicBlock {
+    private class ExitBasicBlock extends BasicBlock {
       ExitBasicBlock() { scopeLast(_, this.getLastElement(), _) }
     }
 

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

@@ -55,8 +55,6 @@ module BaseSsa {
 
     BasicBlock getABasicBlockSuccessor(BasicBlock bb) { result = bb.getASuccessor() }
 
-    class ExitBasicBlock extends BasicBlock, ControlFlow::BasicBlocks::ExitBlock { }
-
     class SourceVariable = PreSsa::SimpleLocalScopeVariable;
 
     predicate variableWrite(BasicBlock bb, int i, SourceVariable v, boolean certain) {

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

@@ -17,8 +17,6 @@ private module SsaInput implements SsaImplCommon::InputSig<Location> {
 
   BasicBlock getABasicBlockSuccessor(BasicBlock bb) { result = bb.getASuccessor() }
 
-  class ExitBasicBlock extends BasicBlock, ControlFlow::BasicBlocks::ExitBlock { }
-
   class SourceVariable = Ssa::SourceVariable;
 
   /**

javascript/ql/lib/semmle/javascript/dataflow/internal/VariableCapture.qll

@@ -240,8 +240,6 @@ module VariableCaptureConfig implements InputSig<js::DbLocation> {
   BasicBlock getImmediateBasicBlockDominator(BasicBlock bb) { result = bb.getImmediateDominator() }
 
   predicate entryBlock(BasicBlock bb) { bb instanceof js::EntryBasicBlock }
-
-  predicate exitBlock(BasicBlock bb) { bb.getLastNode() instanceof js::ControlFlowExitNode }
 }
 
 module VariableCaptureOutput = Flow<js::DbLocation, VariableCaptureConfig>;

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

@@ -14,10 +14,6 @@ module SsaConfig implements InputSig<js::DbLocation> {
 
   class BasicBlock = js::BasicBlock;
 
-  class ExitBasicBlock extends BasicBlock {
-    ExitBasicBlock() { this.isExitBlock() }
-  }
-
   class SourceVariable extends LocalVariableOrThis {
     SourceVariable() { not this.isCaptured() }
   }

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

@@ -18,8 +18,6 @@ module SsaInput implements SsaImplCommon::InputSig<Location> {
 
   BasicBlock getABasicBlockSuccessor(BasicBlock bb) { result = bb.getASuccessor() }
 
-  class ExitBasicBlock extends BasicBlock, BasicBlocks::ExitBasicBlock { }
-
   class SourceVariable = LocalVariable;
 
   /**

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

@@ -47,8 +47,6 @@ module SsaInput implements SsaImplCommon::InputSig<Location> {
 
   BasicBlock getABasicBlockSuccessor(BasicBlock bb) { result = bb.getASuccessor() }
 
-  class ExitBasicBlock = BasicBlocks::ExitBasicBlock;
-
   /**
    * A variable amenable to SSA construction.
    *

shared/dataflow/codeql/dataflow/VariableCapture.qll

@@ -67,9 +67,6 @@ signature module InputSig<LocationSig Location> {
   /** Holds if `bb` is a control-flow entry point. */
   default predicate entryBlock(BasicBlock bb) { not exists(getImmediateBasicBlockDominator(bb)) }
 
-  /** Holds if `bb` is a control-flow exit point. */
-  default predicate exitBlock(BasicBlock bb) { not exists(getABasicBlockSuccessor(bb)) }
-
   /** A variable that is captured in a closure. */
   class CapturedVariable {
     /** Gets a textual representation of this variable. */
@@ -699,10 +696,6 @@ module Flow<LocationSig Location, InputSig<Location> Input> implements OutputSig
       result = Input::getABasicBlockSuccessor(bb)
     }
 
-    class ExitBasicBlock extends BasicBlock {
-      ExitBasicBlock() { exitBlock(this) }
-    }
-
     class SourceVariable = CaptureContainer;
 
     predicate variableWrite(BasicBlock bb, int i, SourceVariable cc, boolean certain) {

shared/ssa/codeql/ssa/Ssa.qll

@@ -60,12 +60,6 @@ signature module InputSig<LocationSig Location> {
   /** Gets an immediate successor of basic block `bb`, if any. */
   BasicBlock getABasicBlockSuccessor(BasicBlock bb);
 
-  /**
-   * An exit basic block, that is, a basic block whose last node is
-   * an exit node.
-   */
-  class ExitBasicBlock extends BasicBlock;
-
   /** A variable that can be SSA converted. */
   class SourceVariable {
     /** Gets a textual representation of this variable. */
@@ -855,6 +849,9 @@ module Make<LocationSig Location, InputSig<Location> Input> {
     lastRefRedef(inp, _, _, def)
   }
 
+  /** Holds if `bb` is a control-flow exit point. */
+  private predicate exitBlock(BasicBlock bb) { not exists(getABasicBlockSuccessor(bb)) }
+
   /**
    * NB: If this predicate is exposed, it should be cached.
    *
@@ -873,7 +870,7 @@ module Make<LocationSig Location, InputSig<Location> Input> {
     lastSsaRefExt(def, _, bb, i) and
     (
       // Can reach exit directly
-      bb instanceof ExitBasicBlock
+      exitBlock(bb)
       or
       // Can reach a block using one or more steps, where `def` is no longer live
       varBlockReachesExitExt(def, bb)
@@ -893,7 +890,7 @@ module Make<LocationSig Location, InputSig<Location> Input> {
     lastSsaRef(def, _, bb, i) and
     (
       // Can reach exit directly
-      bb instanceof ExitBasicBlock
+      exitBlock(bb)
       or
       // Can reach a block using one or more steps, where `def` is no longer live
       varBlockReachesExit(def, bb)