C++: Fix join in AliasedSSA.

Before (on an internal Microsoft repo):
Evaluated relational algebra for predicate AliasedSSA::AllocationMemoryLocation.getVirtualVariable/0#dispred#8debd926@f62ba08v with tuple counts:
      5606472   ~0%    {2} r1 = AliasedSSA::AllocationMemoryLocation#57439a9b_10#join_rhs AND NOT `AliasAnalysis::allocationEscapes/1#93dc9772`(FIRST 1)

      5534569   ~0%    {2} r2 = r1 AND NOT `project#AliasedSSA::getGroupedMemoryLocation/3#14ef79fc#ffbf`(FIRST 1)
  10613026097   ~0%    {2}    | JOIN WITH AliasedSSA::AllocationMemoryLocation#57439a9b_10#join_rhs ON FIRST 1 OUTPUT Rhs.1, Lhs.1
      5534569   ~6%    {2}    | JOIN WITH AliasedSSA::VirtualVariable#5712df39 ON FIRST 1 OUTPUT Lhs.1, Lhs.0

        759836   ~0%    {2} r3 = JOIN AliasedSSA::AllocationMemoryLocation#57439a9b_10#join_rhs WITH `AliasAnalysis::allocationEscapes/1#93dc9772` ON FIRST 1 OUTPUT Lhs.0, Lhs.1
        759832   ~6%    {3}    | JOIN WITH `AliasConfiguration::Allocation.getEnclosingIRFunction/0#dispred#3254a7ee` ON FIRST 1 OUTPUT Rhs.1, _, Lhs.1
        759832   ~0%    {3}    | REWRITE WITH Out.1 := false
        759832   ~1%    {2}    | JOIN WITH num#AliasedSSA::TAllAliasedMemory#4bb632db ON FIRST 2 OUTPUT Rhs.2, Lhs.2
        759832   ~1%    {2}    | JOIN WITH AliasedSSA::VirtualVariable#5712df39 ON FIRST 1 OUTPUT Lhs.1, Lhs.0

      5606472   ~0%    {4} r4 = SCAN r1 OUTPUT In.0, _, _, In.1
      5606472   ~0%    {4}    | REWRITE WITH Out.1 := false, Out.2 := false
        71903   ~5%    {2}    | JOIN WITH `AliasedSSA::getGroupedMemoryLocation/3#14ef79fc#ffbf` ON FIRST 3 OUTPUT Rhs.3, Lhs.3
        71903   ~3%    {2}    | JOIN WITH `AliasedSSA::GroupedMemoryLocation.getVirtualVariable/0#dispred#143f2d1b` ON FIRST 1 OUTPUT Rhs.1, Lhs.1
        71903   ~2%    {2}    | JOIN WITH AliasedSSA::VirtualVariable#5712df39 ON FIRST 1 OUTPUT Lhs.1, Lhs.0

      6366304   ~5%    {2} r5 = r2 UNION r3 UNION r4
                        return r5

After:
[2026-09-03 14:39:34] Evaluated non-recursive predicate AliasedSSA::getAllocationMemoryLocation/1#171552fa@42e30agr in 15ms (size: 505315).
Evaluated relational algebra for predicate AliasedSSA::getAllocationMemoryLocation/1#171552fa@42e30agr with tuple counts:
        505315  ~2%    {2} r1 = JOIN AliasedSSA::VirtualVariable#5712df39 WITH `AliasedSSA::MemoryLocation0.getAnAllocation/0#dispred#f0047858` ON FIRST 1 OUTPUT Rhs.1, Lhs.0
                       return r1

[2026-09-03 14:39:39] Evaluated non-recursive predicate AliasedSSA::AllocationMemoryLocation.getVirtualVariable/0#dispred#8debd926@21855asb in 1811ms (size: 6366304).
Evaluated relational algebra for predicate AliasedSSA::AllocationMemoryLocation.getVirtualVariable/0#dispred#8debd926@21855asb with tuple counts:
        5606472   ~0%    {2} r1 = AliasedSSA::AllocationMemoryLocation#57439a9b_10#join_rhs AND NOT `AliasAnalysis::allocationEscapes/1#93dc9772`(FIRST 1)

        5534569   ~0%    {2} r2 = r1 AND NOT `project#AliasedSSA::getGroupedMemoryLocation/3#14ef79fc#ffbf`(FIRST 1)
        5534569   ~1%    {2}    | JOIN WITH `AliasedSSA::getAllocationMemoryLocation/1#171552fa` ON FIRST 1 OUTPUT Rhs.1, Lhs.1
        5534569   ~6%    {2}    | JOIN WITH AliasedSSA::VirtualVariable#5712df39 ON FIRST 1 OUTPUT Lhs.1, Lhs.0

         759836   ~0%    {2} r3 = JOIN AliasedSSA::AllocationMemoryLocation#57439a9b_10#join_rhs WITH `AliasAnalysis::allocationEscapes/1#93dc9772` ON FIRST 1 OUTPUT Lhs.0, Lhs.1
         759832   ~6%    {3}    | JOIN WITH `AliasConfiguration::Allocation.getEnclosingIRFunction/0#dispred#3254a7ee` ON FIRST 1 OUTPUT Rhs.1, _, Lhs.1
         759832   ~0%    {3}    | REWRITE WITH Out.1 := false
         759832   ~1%    {2}    | JOIN WITH num#AliasedSSA::TAllAliasedMemory#4bb632db ON FIRST 2 OUTPUT Rhs.2, Lhs.2
         759832   ~1%    {2}    | JOIN WITH AliasedSSA::VirtualVariable#5712df39 ON FIRST 1 OUTPUT Lhs.1, Lhs.0

        5606472   ~0%    {4} r4 = SCAN r1 OUTPUT In.0, _, _, In.1
        5606472   ~0%    {4}    | REWRITE WITH Out.1 := false, Out.2 := false
          71903   ~5%    {2}    | JOIN WITH `AliasedSSA::getGroupedMemoryLocation/3#14ef79fc#ffbf` ON FIRST 3 OUTPUT Rhs.3, Lhs.3
          71903   ~3%    {2}    | JOIN WITH `AliasedSSA::GroupedMemoryLocation.getVirtualVariable/0#dispred#143f2d1b` ON FIRST 1 OUTPUT Rhs.1, Lhs.1
          71903   ~2%    {2}    | JOIN WITH AliasedSSA::VirtualVariable#5712df39 ON FIRST 1 OUTPUT Lhs.1, Lhs.0

        6366304   ~5%    {2} r5 = r2 UNION r3 UNION r4
                         return r5

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/ir/implementation/aliased_ssa/internal/AliasedSSA.qll

@@ -295,6 +295,11 @@ abstract class MemoryLocation0 extends TMemoryLocation {
  */
 abstract class VirtualVariable extends MemoryLocation0 { }
 
+pragma[nomagic]
+private VirtualVariable getAllocationMemoryLocation(Allocation alloc) {
+  result.getAnAllocation() = alloc
+}
+
 abstract class AllocationMemoryLocation extends MemoryLocation0 {
   Allocation var;
   boolean isMayAccess;
@@ -313,7 +318,7 @@ abstract class AllocationMemoryLocation extends MemoryLocation0 {
       result = getGroupedMemoryLocation(var, false, false).getVirtualVariable()
       or
       not exists(getGroupedMemoryLocation(var, false, false)) and
-      result.(AllocationMemoryLocation).getAnAllocation() = var
+      result = getAllocationMemoryLocation(var)
     )
   }