C++: IR sanity queries for outgoing edges

These queries have no results on our test cases in the repo, but
`ambiguousSuccessors` has results on any large C++ code base, and
`unexplainedLoop` has results on Windows builds of ChakraCore.

Author: jbj

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

@@ -106,6 +106,32 @@ module InstructionSanity {
     not instr instanceof UnreachedInstruction
   }
 
+  /**
+   * Holds if there are multiple (`n`) edges of kind `kind` from `source`,
+   * where `target` is among the targets of those edges.
+   */
+  query predicate ambiguousSuccessors(
+    Instruction source, EdgeKind kind, int n, Instruction target
+  ) {
+    n = strictcount(Instruction t | source.getSuccessor(kind) = t) and
+    n > 1 and
+    source.getSuccessor(kind) = target
+  }
+
+  /**
+   * Holds if `instr` in `f` is part of a loop even though the AST of `f`
+   * contains no element that can cause loops.
+   */
+  query predicate unexplainedLoop(Function f, Instruction instr) {
+    exists(IRBlock block |
+      instr.getBlock() = block and
+      block.getFunction() = f and
+      block.getASuccessor+() = block
+    ) and
+    not exists(Loop l | l.getEnclosingFunction() = f) and
+    not exists(GotoStmt s | s.getEnclosingFunction() = f)
+  }
+
   /**
    * Holds if a `Phi` instruction is present in a block with fewer than two
    * predecessors.

cpp/ql/src/semmle/code/cpp/ir/implementation/raw/Instruction.qll

@@ -106,6 +106,32 @@ module InstructionSanity {
     not instr instanceof UnreachedInstruction
   }
 
+  /**
+   * Holds if there are multiple (`n`) edges of kind `kind` from `source`,
+   * where `target` is among the targets of those edges.
+   */
+  query predicate ambiguousSuccessors(
+    Instruction source, EdgeKind kind, int n, Instruction target
+  ) {
+    n = strictcount(Instruction t | source.getSuccessor(kind) = t) and
+    n > 1 and
+    source.getSuccessor(kind) = target
+  }
+
+  /**
+   * Holds if `instr` in `f` is part of a loop even though the AST of `f`
+   * contains no element that can cause loops.
+   */
+  query predicate unexplainedLoop(Function f, Instruction instr) {
+    exists(IRBlock block |
+      instr.getBlock() = block and
+      block.getFunction() = f and
+      block.getASuccessor+() = block
+    ) and
+    not exists(Loop l | l.getEnclosingFunction() = f) and
+    not exists(GotoStmt s | s.getEnclosingFunction() = f)
+  }
+
   /**
    * Holds if a `Phi` instruction is present in a block with fewer than two
    * predecessors.

cpp/ql/src/semmle/code/cpp/ir/implementation/unaliased_ssa/Instruction.qll

@@ -106,6 +106,32 @@ module InstructionSanity {
     not instr instanceof UnreachedInstruction
   }
 
+  /**
+   * Holds if there are multiple (`n`) edges of kind `kind` from `source`,
+   * where `target` is among the targets of those edges.
+   */
+  query predicate ambiguousSuccessors(
+    Instruction source, EdgeKind kind, int n, Instruction target
+  ) {
+    n = strictcount(Instruction t | source.getSuccessor(kind) = t) and
+    n > 1 and
+    source.getSuccessor(kind) = target
+  }
+
+  /**
+   * Holds if `instr` in `f` is part of a loop even though the AST of `f`
+   * contains no element that can cause loops.
+   */
+  query predicate unexplainedLoop(Function f, Instruction instr) {
+    exists(IRBlock block |
+      instr.getBlock() = block and
+      block.getFunction() = f and
+      block.getASuccessor+() = block
+    ) and
+    not exists(Loop l | l.getEnclosingFunction() = f) and
+    not exists(GotoStmt s | s.getEnclosingFunction() = f)
+  }
+
   /**
    * Holds if a `Phi` instruction is present in a block with fewer than two
    * predecessors.

cpp/ql/test/library-tests/ir/ir/aliased_ssa_sanity.expected

@@ -3,6 +3,8 @@ unexpectedOperand
 duplicateOperand
 missingPhiOperand
 instructionWithoutSuccessor
+ambiguousSuccessors
+unexplainedLoop
 unnecessaryPhiInstruction
 operandAcrossFunctions
 instructionWithoutUniqueBlock

cpp/ql/test/library-tests/ir/ir/raw_sanity.expected

@@ -3,6 +3,8 @@ unexpectedOperand
 duplicateOperand
 missingPhiOperand
 instructionWithoutSuccessor
+ambiguousSuccessors
+unexplainedLoop
 unnecessaryPhiInstruction
 operandAcrossFunctions
 instructionWithoutUniqueBlock

cpp/ql/test/library-tests/ir/ir/unaliased_ssa_sanity.expected

@@ -3,6 +3,8 @@ unexpectedOperand
 duplicateOperand
 missingPhiOperand
 instructionWithoutSuccessor
+ambiguousSuccessors
+unexplainedLoop
 unnecessaryPhiInstruction
 operandAcrossFunctions
 instructionWithoutUniqueBlock