C++ IR: Don't propagate GVN through non-exact Copy

The `ValueNumbering` library is supposed to propagate value numberings
through a `CopyInstruction` only when it's _congruent_, meaning it must
have exact overlap with its source. A `CopyInstruction` can be a
`LoadInstruction`, a `StoreInstruction`, or a `CopyValueInstruction`.
The latter is also a `UnaryInstruction`, and the value numbering rule
for `UnaryInstruction` applied to it as well.

This meant that value numbering would propagate even through a
non-congruent `CopyValueInstruction`. That's semantically wrong but
probably only an issue in very rare circumstances, and it should get
corrected when we change the definition of `getUnary` to require
congruence.

What's worse is the performance implications. It meant that the value
numbering IPA witness could take two different paths through every
`CopyValueInstruction`. If multiple `CopyValueInstruction`s were
chained, this would lead to an exponential number of variable numbers
for the same `Instruction`, and we would run out of time and space
while performing value numbering.

This fixes the performance of `ValueNumbering.qll` on
https://github.com/asterisk/asterisk, although this project might also
require a separate change for fixing an infinite loop in the IR constant
analysis.

cpp/ql/src/semmle/code/cpp/ir/implementation/aliased_ssa/gvn/ValueNumbering.qll

@@ -124,7 +124,7 @@ private predicate numberableInstruction(Instruction instr) {
   instr instanceof StringConstantInstruction or
   instr instanceof FieldAddressInstruction or
   instr instanceof BinaryInstruction or
-  instr instanceof UnaryInstruction or
+  (instr instanceof UnaryInstruction and not instr instanceof CopyInstruction) or
   instr instanceof PointerArithmeticInstruction or
   instr instanceof CongruentCopyInstruction
 }
@@ -191,6 +191,7 @@ private predicate unaryValueNumber(UnaryInstruction instr, IRFunction irFunc, Op
     Type type, ValueNumber operand) {
   instr.getEnclosingIRFunction() = irFunc and
   (not instr instanceof InheritanceConversionInstruction) and
+  (not instr instanceof CopyInstruction) and
   instr.getOpcode() = opcode and
   instr.getResultType() = type and
   valueNumber(instr.getUnary()) = operand

cpp/ql/src/semmle/code/cpp/ir/implementation/raw/gvn/ValueNumbering.qll

@@ -124,7 +124,7 @@ private predicate numberableInstruction(Instruction instr) {
   instr instanceof StringConstantInstruction or
   instr instanceof FieldAddressInstruction or
   instr instanceof BinaryInstruction or
-  instr instanceof UnaryInstruction or
+  (instr instanceof UnaryInstruction and not instr instanceof CopyInstruction) or
   instr instanceof PointerArithmeticInstruction or
   instr instanceof CongruentCopyInstruction
 }
@@ -191,6 +191,7 @@ private predicate unaryValueNumber(UnaryInstruction instr, IRFunction irFunc, Op
     Type type, ValueNumber operand) {
   instr.getEnclosingIRFunction() = irFunc and
   (not instr instanceof InheritanceConversionInstruction) and
+  (not instr instanceof CopyInstruction) and
   instr.getOpcode() = opcode and
   instr.getResultType() = type and
   valueNumber(instr.getUnary()) = operand

cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/gvn/ValueNumbering.qll

@@ -124,7 +124,7 @@ private predicate numberableInstruction(Instruction instr) {
   instr instanceof StringConstantInstruction or
   instr instanceof FieldAddressInstruction or
   instr instanceof BinaryInstruction or
-  instr instanceof UnaryInstruction or
+  (instr instanceof UnaryInstruction and not instr instanceof CopyInstruction) or
   instr instanceof PointerArithmeticInstruction or
   instr instanceof CongruentCopyInstruction
 }
@@ -191,6 +191,7 @@ private predicate unaryValueNumber(UnaryInstruction instr, IRFunction irFunc, Op
     Type type, ValueNumber operand) {
   instr.getEnclosingIRFunction() = irFunc and
   (not instr instanceof InheritanceConversionInstruction) and
+  (not instr instanceof CopyInstruction) and
   instr.getOpcode() = opcode and
   instr.getResultType() = type and
   valueNumber(instr.getUnary()) = operand