C++: Fix coroutine IR inconsistencies

While here, remove some dead code related to fixed points from the database
scheme.

cpp/ql/lib/semmle/code/cpp/Variable.qll

@@ -409,11 +409,18 @@ class LocalVariable extends LocalScopeVariable, @localvariable {
     exists(ConditionDeclExpr e | e.getVariable() = this and e.getEnclosingFunction() = result)
     or
     orphaned_variables(underlyingElement(this), unresolveElement(result))
+    or
+    coroutine_placeholder_variable(underlyingElement(this), _, unresolveElement(result))
   }
 
   override predicate isStatic() {
     super.isStatic() or orphaned_variables(underlyingElement(this), _)
   }
+
+  override predicate isCompilerGenerated() {
+    super.isCompilerGenerated() or
+    coroutine_placeholder_variable(underlyingElement(this), _, _)
+  }
 }
 
 /**

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -384,11 +384,23 @@ function_return_type(
  */
 coroutine(
   unique int function: @function ref,
-  int traits: @type ref,
-  int handle: @variable ref,
-  int promise: @variable ref
+  int traits: @type ref
 );
 
+/*
+case @coroutine_placeholder_variable.kind of
+  1 = @handle
+| 2 = @promise
+| 3 = @init_await_resume
+;
+*/
+
+coroutine_placeholder_variable(
+  unique int placeholder_variable: @variable ref,
+  int kind: int ref,
+  int function: @function ref
+)
+
 /** The `new` function used for allocating the coroutine state, if any. */
 coroutine_new(
   unique int function: @function ref,
@@ -829,22 +841,6 @@ variable_template_argument_value(
     int arg_value: @expr ref
 );
 
-/*
-  Fixed point types
-  precision(1) = short, precision(2) = default, precision(3) = long
-  is_unsigned(1) = unsigned is_unsigned(2) = signed
-  is_fract_type(1) = declared with _Fract
-  saturating(1) = declared with _Sat
-*/
-/* TODO
-fixedpointtypes(
-    unique int id: @fixedpointtype,
-    int precision: int ref,
-    int is_unsigned: int ref,
-    int is_fract_type: int ref,
-    int saturating: int ref);
-*/
-
 routinetypes(
     unique int id: @routinetype,
     int return_type: @type ref

cpp/ql/lib/upgrades/0fea0ee7026c7c3f7d6faef4df4bf67847b67d71/upgrade.properties

@@ -0,0 +1,4 @@
+description: Improve handling of coroutine placeholder variables
+compatibility: partial
+coroutine.rel: run upgrades.qlo new_coroutine
+coroutine_placeholder_variable.rel: run upgrades.qlo new_coroutine_placeholder_variable

cpp/ql/lib/upgrades/0fea0ee7026c7c3f7d6faef4df4bf67847b67d71/upgrades.ql

@@ -0,0 +1,19 @@
+class Function extends @function {
+  string toString() { none() }
+}
+
+class Type extends @type {
+  string toString() { none() }
+}
+
+class Variable extends @variable {
+  string toString() { none() }
+}
+
+query predicate new_coroutine(Function func, Type traits) { coroutine(func, traits, _, _) }
+
+query predicate new_coroutine_placeholder_variable(Variable var, int kind, Function func) {
+  coroutine(func, _, var, _) and kind = 1
+  or
+  coroutine(func, _, _, var) and kind = 2
+}