C++: Remove this bad materialization:

```
Evaluated relational algebra for predicate _CppType#d1355c92::CppType::hasUnspecifiedType#2#dispred#fff_10#join_rhs_SsaInternals#50208335::DefO__#shared@ec353boa with tuple counts:
  459594    ~0%     {2} r1 = JOIN _IRVariable#e9bf30b2::IRVariable::getAst#0#dispred#ff_Parameter#ed81dd8f::Parameter#f#shared WITH SsaInternalsCommon#3c4fa02d::BaseIRVariable::getIRVariable#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Lhs.1 'arg1', Rhs.1
  461383    ~2%     {3} r2 = JOIN r1 WITH Variable#7a968d4e::Variable::getUnspecifiedType#0#dispred#ff ON FIRST 1 OUTPUT Lhs.0 'arg1', Lhs.1, Rhs.1
  477945    ~6%     {4} r3 = JOIN r2 WITH Variable#7a968d4e::Variable::getUnspecifiedType#0#dispred#ff ON FIRST 1 OUTPUT Lhs.2, Lhs.0 'arg1', Lhs.1, Rhs.1
  346338    ~2%     {4} r4 = JOIN r3 WITH SsaInternalsCommon#3c4fa02d::Indirection::getNumberOfIndirections#0#dispred#ff ON FIRST 1 OUTPUT Lhs.3, Lhs.1 'arg1', Lhs.2, Rhs.1 'arg2'
  178593374 ~0%     {4} r5 = JOIN r4 WITH CppType#d1355c92::CppType::hasUnspecifiedType#2#dispred#fff_10#join_rhs ON FIRST 1 OUTPUT Lhs.2, Lhs.1 'arg1', Lhs.3 'arg2', Rhs.1 'arg3'
  934806228 ~0%     {4} r6 = JOIN r5 WITH SsaInternals#50208335::DefOrUse::getSourceVariable#0#dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Rhs.1 'arg0', Lhs.1 'arg1', Lhs.2 'arg2', Lhs.3 'arg3'
                    return r6

Tuple counts for _DataFlowPrivate#fbdd7bd7::InstructionNode0#class#ff_SsaInternals#50208335::Def#ff_SsaInternals#5020__#antijoin_rhs/4@305d42l5 after 25.6s:
  180185672 ~0%     {4} r1 = JOIN _CppType#d1355c92::CppType::hasUnspecifiedType#2#dispred#fff_10#join_rhs_SsaInternals#50208335::DefO__#shared WITH SsaInternals#50208335::Def#ff ON FIRST 1 OUTPUT Lhs.0 'arg3', Lhs.1 'arg0', Lhs.2 'arg1', Lhs.3 'arg2'
  180185672 ~0%     {5} r2 = JOIN r1 WITH SsaInternals#50208335::Def::getValue#0#dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'arg0', Lhs.2 'arg1', Lhs.3 'arg2', Lhs.0 'arg3'
  180185672 ~0%     {5} r3 = JOIN r2 WITH DataFlowPrivate#fbdd7bd7::InstructionNode0#class#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'arg0', Lhs.2 'arg1', Lhs.3 'arg2', Lhs.4 'arg3'
  178459578 ~1%     {4} r4 = JOIN r3 WITH project#Instruction#577b6a83::InitializeParameterInstruction#ff ON FIRST 1 OUTPUT Lhs.1 'arg0', Lhs.2 'arg1', Lhs.3 'arg2', Lhs.4 'arg3'
                    return r4

Tuple counts for SsaInternals#7b362d2f::TFinalParameterUse#dom#ff/2@9ff4dbcg after 7.9s:
  180185672 ~1%         {4} r1 = JOIN _CppType#d1355c92::CppType::hasUnspecifiedType#2#dispred#fff_10#join_rhs_SsaInternals#50208335::DefO__#shared WITH SsaInternals#50208335::Def#ff ON FIRST 1 OUTPUT Lhs.1 'p', Lhs.2, Lhs.3, Lhs.0
  1726094   ~0%         {4} r2 = r1 AND NOT _DataFlowPrivate#fbdd7bd7::InstructionNode0#class#ff_SsaInternals#50208335::Def#ff_SsaInternals#5020__#antijoin_rhs(Lhs.0 'p', Lhs.1, Lhs.2, Lhs.3)
  1726094   ~54%        {4} r3 = SCAN r2 OUTPUT In.0 'p', In.1, In.2, 1
  1769636   ~54%        {5} r4 = JOIN r3 WITH PRIMITIVE range#bbf ON Lhs.3,Lhs.1

  1769636   ~45%        {4} r5 = SCAN r4 OUTPUT In.2, (In.4 'indirectionIndex' + 1), In.0 'p', In.4 'indirectionIndex'
  591253    ~11541%     {2} r6 = JOIN r5 WITH SsaInternalsCommon#3c4fa02d::isModifiableAtImpl#2#ff ON FIRST 2 OUTPUT Lhs.2 'p', Lhs.3 'indirectionIndex'

  1769636   ~52%        {4} r7 = SCAN r4 OUTPUT In.2, In.0 'p', In.4 'indirectionIndex', (In.4 'indirectionIndex' + 1)
  1724893   ~41%        {5} r8 = JOIN r7 WITH CppType#d1355c92::CppType::hasType#2#dispred#fff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'p', Lhs.0, Lhs.2 'indirectionIndex', Lhs.3
  1718843   ~46%        {5} r9 = JOIN r8 WITH Type#2e8eb3ef::Type::stripType#0#dispred#ff ON FIRST 1 OUTPUT Rhs.1, Lhs.1 'p', Lhs.2, Lhs.3 'indirectionIndex', Lhs.4
  8608      ~0%         {5} r10 = JOIN r9 WITH SmartPointer#917721ba::SmartPtr#f ON FIRST 1 OUTPUT Lhs.1 'p', Lhs.2, Lhs.3 'indirectionIndex', Lhs.4, Lhs.0
  8608      ~0%         {5} r11 = r10 AND NOT PointerWrapper#7cc81d2d::PointerWrapper::pointsToConst#0#dispred#f(Lhs.4)
  8608      ~4986%      {2} r12 = SCAN r11 OUTPUT In.0 'p', In.2 'indirectionIndex'

  599861    ~11711%     {2} r13 = r6 UNION r12
                        return r13
```

Author: MathiasVP

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

@@ -169,19 +169,21 @@ private newtype TDefOrUseImpl =
     // Avoid creating parameter nodes if there is no definitions of the variable other than the initializaion.
     exists(SsaInternals0::Def def |
       def.getSourceVariable().getBaseVariable().(BaseIRVariable).getIRVariable().getAst() = p and
-      not def.getValue().asInstruction() instanceof InitializeParameterInstruction
-    ) and
-    // If the type is modifiable
-    exists(CppType cppType |
-      cppType.hasUnspecifiedType(p.getUnspecifiedType(), _) and
-      isModifiableAt(cppType, indirectionIndex + 1)
-    ) and
-    exists(Indirection indirection |
-      indirection.getType() = p.getUnspecifiedType() and
-      indirectionIndex = [1 .. indirection.getNumberOfIndirections()]
+      not def.getValue().asInstruction() instanceof InitializeParameterInstruction and
+      unspecifiedTypeIsModifiableAt(p.getUnspecifiedType(), indirectionIndex)
     )
   }
 
+private predicate unspecifiedTypeIsModifiableAt(Type unspecified, int indirectionIndex) {
+  indirectionIndex = [1 .. getIndirectionForUnspecifiedType(unspecified).getNumberOfIndirections()] and
+  exists(CppType cppType |
+    cppType.hasUnspecifiedType(unspecified, _) and
+    isModifiableAt(cppType, indirectionIndex + 1)
+  )
+}
+
+private Indirection getIndirectionForUnspecifiedType(Type t) { result.getType() = t }
+
 abstract private class DefOrUseImpl extends TDefOrUseImpl {
   /** Gets a textual representation of this element. */
   abstract string toString();