C++: Fix joins in isModifiableAtImpl

[MathiasVP]

Also highlighted by the DCA join order report. This on was actually quite bad 😅.

Before:

[2023-12-18 10:09:33] Evaluated non-recursive predicate SsaInternalsCommon::isModifiableAtImpl/2#2b25ad2f@b02f6ccj in 71404ms (size: 2842043).
Evaluated relational algebra for predicate SsaInternalsCommon::isModifiableAtImpl/2#2b25ad2f@b02f6ccj with tuple counts:
      4208191   ~1%    {2} r1 = JOIN CppType::TCppType#eff8d274 WITH `CppType::CppType.hasType/2#dispred#d3f6ee89` ON FIRST 1 OUTPUT Rhs.1, Lhs.0
      4207753   ~0%    {2} r2 = JOIN r1 WITH `Type::Type.getUnderlyingType/0#dispred#bd141f6a` ON FIRST 1 OUTPUT Rhs.1, Lhs.1
   2914047693   ~0%    {3} r3 = JOIN r2 WITH `Type::Type.getUnderlyingType/0#dispred#bd141f6a_10#join_rhs` ON FIRST 1 OUTPUT Rhs.1, Lhs.1, Lhs.0
                  
      1280304   ~0%    {3} r4 = JOIN r3 WITH `SsaInternalsCommon::isIndirectionType/1#6f5ae315` ON FIRST 1 OUTPUT Lhs.2, _, Lhs.1
      1280304   ~0%    {3} r5 = REWRITE r4 WITH Out.1 := 0
      1280304   ~2%    {2} r6 = JOIN r5 WITH `DataFlowUtil::getTypeImpl0/2#26c3c2a8` ON FIRST 2 OUTPUT Rhs.2, Lhs.2
                  
      1280304   ~2%    {2} r7 = JOIN r3 WITH `SsaInternalsCommon::isIndirectionType/1#6f5ae315` ON FIRST 1 OUTPUT Lhs.2, Lhs.1
            0   ~0%    {2} r8 = r7 AND NOT `_project#DataFlowUtil::getTypeImpl0/2#26c3c2a8_10#join_rhs#antijoin_rhs`(FIRST 1)
                  
            0   ~0%    {2} r9 = JOIN r8 WITH Type::UnknownType#cbea2ba5 CARTESIAN PRODUCT OUTPUT Rhs.0, Lhs.1
                  
      1280304   ~2%    {2} r10 = r6 UNION r9
                        {2} r11 = r10 AND NOT `_Type::Type.hasSpecifier/1#dispred#d2911bb1#fb_10#join_rhs#antijoin_rhs`(FIRST 1)
      1280304   ~0%    {2} r12 = SCAN r11 OUTPUT In.1, _
      1280304   ~2%    {2} r13 = REWRITE r12 WITH Out.1 := 0
                  
            0   ~0%    {1} r14 = SCAN r8 OUTPUT In.1
            0   ~0%    {2} r15 = JOIN r14 WITH Type::UnknownType#cbea2ba5 CARTESIAN PRODUCT OUTPUT Rhs.0, Lhs.0
                  
      1280304   ~2%    {2} r16 = r6 UNION r15
      1279800   ~0%    {2} r17 = JOIN r16 WITH `Type::Type.stripType/0#dispred#e1299c1e` ON FIRST 1 OUTPUT Rhs.1, Lhs.1
      212168   ~0%    {2} r18 = JOIN r17 WITH `project#Class::Class.getAField/0#dispred#19444341` ON FIRST 1 OUTPUT Lhs.1, _
      212168   ~0%    {2} r19 = REWRITE r18 WITH Out.1 := 0
                  
      1492472  ~19%    {2} r20 = r13 UNION r19
                  
      3054211   ~7%    {2} r21 = `SsaInternalsCommon::isModifiableAtImplAtLeast1/2#bae9353a` UNION r20
                        return r21

After:

[2023-12-18 11:59:51] Evaluated non-recursive predicate SsaInternalsCommon::isModifiableAtImpl/2#2b25ad2f@aa81f0vi in 995ms (size: 2842043).
Evaluated relational algebra for predicate SsaInternalsCommon::isModifiableAtImpl/2#2b25ad2f@aa81f0vi with tuple counts:
      4208191   ~1%    {2} r1 = JOIN CppType::TCppType#eff8d274 WITH `CppType::CppType.hasType/2#dispred#d3f6ee89` ON FIRST 1 OUTPUT Rhs.1, Lhs.0
      4207753   ~0%    {2} r2 = JOIN r1 WITH `Type::Type.getUnderlyingType/0#dispred#bd141f6a` ON FIRST 1 OUTPUT Rhs.1, Lhs.1
      1280304   ~2%    {2} r3 = JOIN r2 WITH `SsaInternalsCommon::isUnderlyingIndirectionType/1#14660e47` ON FIRST 1 OUTPUT Lhs.0, Lhs.1
                  
      1280304   ~0%    {3} r4 = JOIN r3 WITH `ResolveClass::isType/1#eabb9878` ON FIRST 1 OUTPUT Lhs.0, _, Lhs.1
      1280304   ~0%    {3} r5 = REWRITE r4 WITH Out.1 := 0
      1280304   ~2%    {2} r6 = JOIN r5 WITH `DataFlowUtil::getTypeImpl0/2#26c3c2a8` ON FIRST 2 OUTPUT Rhs.2, Lhs.2
                  
      1280304   ~2%    {2} r7 = JOIN r3 WITH `ResolveClass::isType/1#eabb9878` ON FIRST 1 OUTPUT Lhs.0, Lhs.1
                        {2} r8 = r7 AND NOT `_project#DataFlowUtil::getTypeImpl0/2#26c3c2a8_10#join_rhs#antijoin_rhs`(FIRST 1)
            0   ~0%    {1} r9 = SCAN r8 OUTPUT In.1
            0   ~0%    {2} r10 = JOIN r9 WITH Type::UnknownType#cbea2ba5 CARTESIAN PRODUCT OUTPUT Rhs.0, Lhs.0
                  
      1280304   ~2%    {2} r11 = r6 UNION r10
      1280304   ~2%    {2} r12 = JOIN r11 WITH `ResolveClass::isType/1#eabb9878` ON FIRST 1 OUTPUT Lhs.0, Lhs.1
                  
                        {2} r13 = r12 AND NOT `_Type::Type.hasSpecifier/1#dispred#d2911bb1#fb_10#join_rhs#antijoin_rhs`(FIRST 1)
      1280304   ~0%    {2} r14 = SCAN r13 OUTPUT In.1, _
      1280304   ~2%    {2} r15 = REWRITE r14 WITH Out.1 := 0
                  
      1279800   ~0%    {2} r16 = JOIN r12 WITH `Type::Type.stripType/0#dispred#e1299c1e` ON FIRST 1 OUTPUT Rhs.1, Lhs.1
      212168   ~0%    {2} r17 = JOIN r16 WITH `project#Class::Class.getAField/0#dispred#19444341` ON FIRST 1 OUTPUT Lhs.1, _
      212168   ~0%    {2} r18 = REWRITE r17 WITH Out.1 := 0
                  
      1492472  ~19%    {2} r19 = r15 UNION r18
                  
      3054211   ~7%    {2} r20 = `SsaInternalsCommon::isModifiableAtImplAtLeast1/2#bae9353a` UNION r19
                         return r20

[jketema]

LGTM if DCA is happy.