C++: Move TIRVariable to its own file

The `SSAConstruction.getNewIRVariable` was very slow on Wireshark. This
was probably because it couldn't join on multiple columns
simultaneously. Instead of improving the join, I observed that the
`TIRVariable` type was the same between all three IR stages except for a
few occurrences of `FunctionIR` that could easily be changed to
`Function`. By sharing `TIRVariable` between all the stages, we avoid
recomputing it and translating it between every stage, turning the slow
`getNewIRVariable` predicate into a no-op.

This change means that later stages of the IR can't introduce new
variables, but that was already the case because
`config/identical-files.json` forced all three `IRVariable.qll` files to
be identical.

Author: jbj

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/IRVariable.qll

@@ -3,31 +3,7 @@ import FunctionIR
 import cpp
 import semmle.code.cpp.ir.implementation.TempVariableTag
 private import semmle.code.cpp.ir.internal.TempVariableTag
-
-private newtype TIRVariable =
-  TIRAutomaticUserVariable(LocalScopeVariable var, FunctionIR funcIR) {
-    exists(Function func |
-      func = funcIR.getFunction() and
-      (
-        var.getFunction() = func or
-        var.(Parameter).getCatchBlock().getEnclosingFunction() = func
-      )
-    )
-  } or
-  TIRStaticUserVariable(Variable var, FunctionIR funcIR) {
-    (
-      var instanceof GlobalOrNamespaceVariable or
-      var instanceof MemberVariable and not var instanceof Field
-    ) and
-    exists(VariableAccess access |
-      access.getTarget() = var and
-      access.getEnclosingFunction() = funcIR.getFunction()
-    )
-  } or
-  TIRTempVariable(FunctionIR funcIR, Locatable ast, TempVariableTag tag, 
-    Type type) {
-    Construction::hasTempVariable(funcIR.getFunction(), ast, tag, type)
-  }
+private import semmle.code.cpp.ir.internal.TIRVariable
 
 IRUserVariable getIRUserVariable(Function func, Variable var) {
   result.getVariable() = var and
@@ -40,7 +16,7 @@ IRUserVariable getIRUserVariable(Function func, Variable var) {
  * generated by the AST-to-IR translation (`IRTempVariable`).
  */
 abstract class IRVariable extends TIRVariable {
-  FunctionIR funcIR;
+  Function func;
 
   abstract string toString();
 
@@ -72,14 +48,14 @@ abstract class IRVariable extends TIRVariable {
    * Gets the IR for the function that references this variable.
    */
   final FunctionIR getFunctionIR() {
-    result = funcIR
+    result.getFunction() = func
   }
 
   /**
    * Gets the function that references this variable.
    */
   final Function getFunction() {
-    result = funcIR.getFunction()
+    result = func
   }
 }
 
@@ -126,7 +102,7 @@ class IRAutomaticUserVariable extends IRUserVariable, IRAutomaticVariable,
   LocalScopeVariable localVar;
 
   IRAutomaticUserVariable() {
-    this = TIRAutomaticUserVariable(localVar, funcIR) and
+    this = TIRAutomaticUserVariable(localVar, func) and
     var = localVar
   }
 
@@ -137,7 +113,7 @@ class IRAutomaticUserVariable extends IRUserVariable, IRAutomaticVariable,
 
 class IRStaticUserVariable extends IRUserVariable, TIRStaticUserVariable {
   IRStaticUserVariable() {
-    this = TIRStaticUserVariable(var, funcIR)
+    this = TIRStaticUserVariable(var, func)
   }
 }
 
@@ -152,7 +128,7 @@ class IRTempVariable extends IRVariable, IRAutomaticVariable, TIRTempVariable {
   Type type;
 
   IRTempVariable() {
-    this = TIRTempVariable(funcIR, ast, tag, type)
+    this = TIRTempVariable(func, ast, tag, type)
   }
 
   override final Type getType() {

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/internal/SSAConstruction.qll

@@ -71,20 +71,8 @@ cached private module Cached {
   }
 
   private IRVariable getNewIRVariable(OldIR::IRVariable var) {
-    result.getFunction() = var.getFunction() and
-    (
-      exists(OldIR::IRUserVariable userVar, IRUserVariable newUserVar |
-        userVar = var and
-        newUserVar.getVariable() = userVar.getVariable() and
-        result = newUserVar
-      ) or
-      exists(OldIR::IRTempVariable tempVar, IRTempVariable newTempVar |
-        tempVar = var and
-        newTempVar.getAST() = tempVar.getAST() and
-        newTempVar.getTag() = tempVar.getTag() and
-        result = newTempVar
-      )
-    )
+    // This is just a type cast. Both classes derive from the same newtype.
+    result = var
   }
 
   cached newtype TInstruction =

cpp/ql/src/semmle/code/cpp/ir/implementation/raw/IRVariable.qll

@@ -3,31 +3,7 @@ import FunctionIR
 import cpp
 import semmle.code.cpp.ir.implementation.TempVariableTag
 private import semmle.code.cpp.ir.internal.TempVariableTag
-
-private newtype TIRVariable =
-  TIRAutomaticUserVariable(LocalScopeVariable var, FunctionIR funcIR) {
-    exists(Function func |
-      func = funcIR.getFunction() and
-      (
-        var.getFunction() = func or
-        var.(Parameter).getCatchBlock().getEnclosingFunction() = func
-      )
-    )
-  } or
-  TIRStaticUserVariable(Variable var, FunctionIR funcIR) {
-    (
-      var instanceof GlobalOrNamespaceVariable or
-      var instanceof MemberVariable and not var instanceof Field
-    ) and
-    exists(VariableAccess access |
-      access.getTarget() = var and
-      access.getEnclosingFunction() = funcIR.getFunction()
-    )
-  } or
-  TIRTempVariable(FunctionIR funcIR, Locatable ast, TempVariableTag tag, 
-    Type type) {
-    Construction::hasTempVariable(funcIR.getFunction(), ast, tag, type)
-  }
+private import semmle.code.cpp.ir.internal.TIRVariable
 
 IRUserVariable getIRUserVariable(Function func, Variable var) {
   result.getVariable() = var and
@@ -40,7 +16,7 @@ IRUserVariable getIRUserVariable(Function func, Variable var) {
  * generated by the AST-to-IR translation (`IRTempVariable`).
  */
 abstract class IRVariable extends TIRVariable {
-  FunctionIR funcIR;
+  Function func;
 
   abstract string toString();
 
@@ -72,14 +48,14 @@ abstract class IRVariable extends TIRVariable {
    * Gets the IR for the function that references this variable.
    */
   final FunctionIR getFunctionIR() {
-    result = funcIR
+    result.getFunction() = func
   }
 
   /**
    * Gets the function that references this variable.
    */
   final Function getFunction() {
-    result = funcIR.getFunction()
+    result = func
   }
 }
 
@@ -126,7 +102,7 @@ class IRAutomaticUserVariable extends IRUserVariable, IRAutomaticVariable,
   LocalScopeVariable localVar;
 
   IRAutomaticUserVariable() {
-    this = TIRAutomaticUserVariable(localVar, funcIR) and
+    this = TIRAutomaticUserVariable(localVar, func) and
     var = localVar
   }
 
@@ -137,7 +113,7 @@ class IRAutomaticUserVariable extends IRUserVariable, IRAutomaticVariable,
 
 class IRStaticUserVariable extends IRUserVariable, TIRStaticUserVariable {
   IRStaticUserVariable() {
-    this = TIRStaticUserVariable(var, funcIR)
+    this = TIRStaticUserVariable(var, func)
   }
 }
 
@@ -152,7 +128,7 @@ class IRTempVariable extends IRVariable, IRAutomaticVariable, TIRTempVariable {
   Type type;
 
   IRTempVariable() {
-    this = TIRTempVariable(funcIR, ast, tag, type)
+    this = TIRTempVariable(func, ast, tag, type)
   }
 
   override final Type getType() {

cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/IRVariable.qll

@@ -3,31 +3,7 @@ import FunctionIR
 import cpp
 import semmle.code.cpp.ir.implementation.TempVariableTag
 private import semmle.code.cpp.ir.internal.TempVariableTag
-
-private newtype TIRVariable =
-  TIRAutomaticUserVariable(LocalScopeVariable var, FunctionIR funcIR) {
-    exists(Function func |
-      func = funcIR.getFunction() and
-      (
-        var.getFunction() = func or
-        var.(Parameter).getCatchBlock().getEnclosingFunction() = func
-      )
-    )
-  } or
-  TIRStaticUserVariable(Variable var, FunctionIR funcIR) {
-    (
-      var instanceof GlobalOrNamespaceVariable or
-      var instanceof MemberVariable and not var instanceof Field
-    ) and
-    exists(VariableAccess access |
-      access.getTarget() = var and
-      access.getEnclosingFunction() = funcIR.getFunction()
-    )
-  } or
-  TIRTempVariable(FunctionIR funcIR, Locatable ast, TempVariableTag tag, 
-    Type type) {
-    Construction::hasTempVariable(funcIR.getFunction(), ast, tag, type)
-  }
+private import semmle.code.cpp.ir.internal.TIRVariable
 
 IRUserVariable getIRUserVariable(Function func, Variable var) {
   result.getVariable() = var and
@@ -40,7 +16,7 @@ IRUserVariable getIRUserVariable(Function func, Variable var) {
  * generated by the AST-to-IR translation (`IRTempVariable`).
  */
 abstract class IRVariable extends TIRVariable {
-  FunctionIR funcIR;
+  Function func;
 
   abstract string toString();
 
@@ -72,14 +48,14 @@ abstract class IRVariable extends TIRVariable {
    * Gets the IR for the function that references this variable.
    */
   final FunctionIR getFunctionIR() {
-    result = funcIR
+    result.getFunction() = func
   }
 
   /**
    * Gets the function that references this variable.
    */
   final Function getFunction() {
-    result = funcIR.getFunction()
+    result = func
   }
 }
 
@@ -126,7 +102,7 @@ class IRAutomaticUserVariable extends IRUserVariable, IRAutomaticVariable,
   LocalScopeVariable localVar;
 
   IRAutomaticUserVariable() {
-    this = TIRAutomaticUserVariable(localVar, funcIR) and
+    this = TIRAutomaticUserVariable(localVar, func) and
     var = localVar
   }
 
@@ -137,7 +113,7 @@ class IRAutomaticUserVariable extends IRUserVariable, IRAutomaticVariable,
 
 class IRStaticUserVariable extends IRUserVariable, TIRStaticUserVariable {
   IRStaticUserVariable() {
-    this = TIRStaticUserVariable(var, funcIR)
+    this = TIRStaticUserVariable(var, func)
   }
 }
 
@@ -152,7 +128,7 @@ class IRTempVariable extends IRVariable, IRAutomaticVariable, TIRTempVariable {
   Type type;
 
   IRTempVariable() {
-    this = TIRTempVariable(funcIR, ast, tag, type)
+    this = TIRTempVariable(func, ast, tag, type)
   }
 
   override final Type getType() {

cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/internal/SSAConstruction.qll

@@ -71,20 +71,8 @@ cached private module Cached {
   }
 
   private IRVariable getNewIRVariable(OldIR::IRVariable var) {
-    result.getFunction() = var.getFunction() and
-    (
-      exists(OldIR::IRUserVariable userVar, IRUserVariable newUserVar |
-        userVar = var and
-        newUserVar.getVariable() = userVar.getVariable() and
-        result = newUserVar
-      ) or
-      exists(OldIR::IRTempVariable tempVar, IRTempVariable newTempVar |
-        tempVar = var and
-        newTempVar.getAST() = tempVar.getAST() and
-        newTempVar.getTag() = tempVar.getTag() and
-        result = newTempVar
-      )
-    )
+    // This is just a type cast. Both classes derive from the same newtype.
+    result = var
   }
 
   cached newtype TInstruction =

cpp/ql/src/semmle/code/cpp/ir/internal/TIRVariable.qll

@@ -0,0 +1,23 @@
+private import cpp
+private import semmle.code.cpp.ir.implementation.TempVariableTag
+private import semmle.code.cpp.ir.implementation.raw.internal.IRConstruction as Construction
+
+newtype TIRVariable =
+  TIRAutomaticUserVariable(LocalScopeVariable var, Function func) {
+    var.getFunction() = func or
+    var.(Parameter).getCatchBlock().getEnclosingFunction() = func
+  } or
+  TIRStaticUserVariable(Variable var, Function func) {
+    (
+      var instanceof GlobalOrNamespaceVariable or
+      var instanceof MemberVariable and not var instanceof Field
+    ) and
+    exists(VariableAccess access |
+      access.getTarget() = var and
+      access.getEnclosingFunction() = func
+    )
+  } or
+  TIRTempVariable(Function func, Locatable ast, TempVariableTag tag, Type type) {
+    Construction::hasTempVariable(func, ast, tag, type)
+  }
+