C++: Improve 'toString' on the 'InitializeGroup' instruction.

cpp/ql/lib/semmle/code/cpp/ir/implementation/aliased_ssa/Instruction.qll

@@ -2167,6 +2167,18 @@ class ChiInstruction extends Instruction {
  */
 class InitializeGroupInstruction extends Instruction {
   InitializeGroupInstruction() { this.getOpcode() instanceof Opcode::InitializeGroup }
+
+  /**
+   * Gets an `IRVariable` whose memory is initialized by this instruction, if any.
+   * Note: Allocations that are not represented as `IRVariable`s (such as
+   * dynamic allocations) are not returned by this predicate even if this
+   * instruction initializes such memory.
+   */
+  final IRVariable getAnIRVariable() { result = Construction::getAnInitializeGroupVariable(this) }
+
+  final override string getImmediateString() {
+    result = strictconcat(this.getAnIRVariable().toString(), ",")
+  }
 }
 
 /**

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

@@ -263,6 +263,14 @@ private module Cached {
     )
   }
 
+  cached
+  IRVariable getAnInitializeGroupVariable(InitializeGroupInstruction init) {
+    exists(Alias::VariableGroup vg |
+      init = initializeGroup(vg) and
+      result = vg.getAnAllocation().getABaseInstruction().(VariableInstruction).getIRVariable()
+    )
+  }
+
   /**
    * Holds if `instr` is part of a cycle in the operand graph that doesn't go
    * through a phi instruction and therefore should be impossible.

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/IRConstruction.qll

@@ -407,6 +407,8 @@ predicate hasUnreachedInstruction(IRFunction func) {
   )
 }
 
+IRVariable getAnInitializeGroupVariable(InitializeGroupInstruction instr) { none() }
+
 import CachedForDebugging
 
 cached

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

@@ -263,6 +263,9 @@ private module Cached {
     )
   }
 
+  cached
+  IRVariable getAnInitializeGroupVariable(InitializeGroupInstruction instr) { none() }
+
   /**
    * Holds if `instr` is part of a cycle in the operand graph that doesn't go
    * through a phi instruction and therefore should be impossible.