Merge pull request #12982 from rdmarsh2/rdmarsh2/ir-guards-unreached

C++: Handle nonreturning functions in IR generation

csharp/ql/src/experimental/ir/implementation/internal/TInstruction.qll

@@ -19,6 +19,9 @@ newtype TInstruction =
   ) {
     IRConstruction::Raw::hasInstruction(tag1, tag2)
   } or
+  TRawUnreachedInstruction(IRFunctionBase irFunc) {
+    IRConstruction::hasUnreachedInstruction(irFunc)
+  } or
   TUnaliasedSsaPhiInstruction(
     TRawInstruction blockStartInstr, UnaliasedSsa::Ssa::MemoryLocation memoryLocation
   ) {

csharp/ql/src/experimental/ir/implementation/raw/internal/IRConstruction.qll

@@ -414,6 +414,8 @@ private module Cached {
   }
 }
 
+predicate hasUnreachedInstruction(IRFunction func) { none() }
+
 import CachedForDebugging
 
 cached

csharp/ql/src/experimental/ir/implementation/unaliased_ssa/internal/SSAConstruction.qll

@@ -34,9 +34,13 @@ private module Cached {
 
   cached
   predicate hasUnreachedInstructionCached(IRFunction irFunc) {
-    exists(OldInstruction oldInstruction |
+    exists(OldIR::Instruction oldInstruction |
       irFunc = oldInstruction.getEnclosingIRFunction() and
-      Reachability::isInfeasibleInstructionSuccessor(oldInstruction, _)
+      (
+        Reachability::isInfeasibleInstructionSuccessor(oldInstruction, _)
+        or
+        oldInstruction.getOpcode() instanceof Opcode::Unreached
+      )
     )
   }
 
@@ -366,21 +370,19 @@ private module Cached {
     then
       result = getChi(getOldInstruction(instruction)) and
       kind instanceof GotoEdge
-    else (
+    else
       exists(OldInstruction oldInstruction |
-        oldInstruction = getOldInstruction(instruction) and
+        (
+          oldInstruction = getOldInstruction(instruction)
+          or
+          instruction = getChi(oldInstruction)
+        ) and
         (
           if Reachability::isInfeasibleInstructionSuccessor(oldInstruction, kind)
           then result = unreachedInstruction(instruction.getEnclosingIRFunction())
           else result = getNewInstruction(oldInstruction.getSuccessor(kind))
         )
       )
-      or
-      exists(OldInstruction oldInstruction |
-        instruction = getChi(oldInstruction) and
-        result = getNewInstruction(oldInstruction.getSuccessor(kind))
-      )
-    )
   }
 
   cached