C++: Add a couple test cases for unreachable code in IR

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

@@ -6668,3 +6668,63 @@ ir.cpp:
 # 1018|           -1: p
 # 1018|               Type = Point *
 # 1018|               ValueCategory = prvalue(load)
+# 1021| UnreachableViaGoto() -> int
+# 1021|   params: 
+# 1021|   body: { ... }
+# 1022|     0: goto ...
+# 1023|     1: return ...
+# 1023|       0: 1
+# 1023|           Type = int
+# 1023|           Value = 1
+# 1023|           ValueCategory = prvalue
+# 1024|     2: label ...:
+# 1025|     3: return ...
+# 1025|       0: 0
+# 1025|           Type = int
+# 1025|           Value = 0
+# 1025|           ValueCategory = prvalue
+# 1028| UnreachableIf(bool) -> int
+# 1028|   params: 
+# 1028|     0: b
+# 1028|         Type = bool
+# 1028|   body: { ... }
+# 1029|     0: if (...) ... 
+# 1029|       0: b
+# 1029|           Type = bool
+# 1029|           ValueCategory = prvalue(load)
+# 1029|       1: { ... }
+# 1030|         0: if (...) ... 
+# 1030|           0: 0
+# 1030|               Type = bool
+# 1030|               Value = 0
+# 1030|               ValueCategory = prvalue
+# 1030|           1: { ... }
+# 1031|             0: return ...
+# 1031|               0: 1
+# 1031|                   Type = int
+# 1031|                   Value = 1
+# 1031|                   ValueCategory = prvalue
+# 1033|           2: { ... }
+# 1034|             0: return ...
+# 1034|               0: 0
+# 1034|                   Type = int
+# 1034|                   Value = 0
+# 1034|                   ValueCategory = prvalue
+# 1037|       2: { ... }
+# 1038|         0: if (...) ... 
+# 1038|           0: 1
+# 1038|               Type = bool
+# 1038|               Value = 1
+# 1038|               ValueCategory = prvalue
+# 1038|           1: { ... }
+# 1039|             0: return ...
+# 1039|               0: 0
+# 1039|                   Type = int
+# 1039|                   Value = 0
+# 1039|                   ValueCategory = prvalue
+# 1041|           2: { ... }
+# 1042|             0: return ...
+# 1042|               0: 1
+# 1042|                   Type = int
+# 1042|                   Value = 1
+# 1042|                   ValueCategory = prvalue

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

@@ -4618,3 +4618,84 @@ ir.cpp:
 # 1005|     v6_13(void)          = ReturnValue              : r6_12, m6_11
 # 1005|     v6_14(void)          = UnmodeledUse             : mu*
 # 1005|     v6_15(void)          = ExitFunction             : 
+
+# 1021| UnreachableViaGoto() -> int
+# 1021|   Block 0
+# 1021|     v0_0(void)       = EnterFunction            : 
+# 1021|     m0_1(unknown)    = AliasedDefinition        : 
+# 1021|     mu0_2(unknown)   = UnmodeledDefinition      : 
+# 1022|     v0_3(void)       = NoOp                     : 
+# 1024|     v0_4(void)       = NoOp                     : 
+# 1025|     r0_5(glval<int>) = VariableAddress[#return] : 
+# 1025|     r0_6(int)        = Constant[0]              : 
+# 1025|     m0_7(int)        = Store                    : r0_5, r0_6
+#-----|   Goto -> Block 1
+
+# 1021|   Block 1
+# 1021|     m1_0(int)        = Phi                      : from 0:m0_7, from 2:m2_2
+# 1021|     r1_1(glval<int>) = VariableAddress[#return] : 
+# 1021|     v1_2(void)       = ReturnValue              : r1_1, m1_0
+# 1021|     v1_3(void)       = UnmodeledUse             : mu*
+# 1021|     v1_4(void)       = ExitFunction             : 
+
+# 1023|   Block 2
+# 1023|     r2_0(glval<int>) = VariableAddress[#return] : 
+# 1023|     r2_1(int)        = Constant[1]              : 
+# 1023|     m2_2(int)        = Store                    : r2_0, r2_1
+#-----|   Goto -> Block 1
+
+# 1028| UnreachableIf(bool) -> int
+# 1028|   Block 0
+# 1028|     v0_0(void)        = EnterFunction          : 
+# 1028|     m0_1(unknown)     = AliasedDefinition      : 
+# 1028|     mu0_2(unknown)    = UnmodeledDefinition    : 
+# 1028|     r0_3(glval<bool>) = VariableAddress[b]     : 
+# 1028|     m0_4(bool)        = InitializeParameter[b] : r0_3
+# 1029|     r0_5(glval<bool>) = VariableAddress[b]     : 
+# 1029|     r0_6(bool)        = Load                   : r0_5, m0_4
+# 1029|     v0_7(void)        = ConditionalBranch      : r0_6
+#-----|   False -> Block 5
+#-----|   True -> Block 2
+
+# 1028|   Block 1
+# 1028|     m1_0(int)        = Phi                      : from 3:m3_2, from 4:m4_2, from 6:m6_2, from 7:m7_2
+# 1028|     r1_1(glval<int>) = VariableAddress[#return] : 
+# 1028|     v1_2(void)       = ReturnValue              : r1_1, m1_0
+# 1028|     v1_3(void)       = UnmodeledUse             : mu*
+# 1028|     v1_4(void)       = ExitFunction             : 
+
+# 1030|   Block 2
+# 1030|     r2_0(bool) = Constant[0]       : 
+# 1030|     v2_1(void) = ConditionalBranch : r2_0
+#-----|   False -> Block 4
+#-----|   True -> Block 3
+
+# 1031|   Block 3
+# 1031|     r3_0(glval<int>) = VariableAddress[#return] : 
+# 1031|     r3_1(int)        = Constant[1]              : 
+# 1031|     m3_2(int)        = Store                    : r3_0, r3_1
+#-----|   Goto -> Block 1
+
+# 1034|   Block 4
+# 1034|     r4_0(glval<int>) = VariableAddress[#return] : 
+# 1034|     r4_1(int)        = Constant[0]              : 
+# 1034|     m4_2(int)        = Store                    : r4_0, r4_1
+#-----|   Goto -> Block 1
+
+# 1038|   Block 5
+# 1038|     r5_0(bool) = Constant[1]       : 
+# 1038|     v5_1(void) = ConditionalBranch : r5_0
+#-----|   False -> Block 7
+#-----|   True -> Block 6
+
+# 1039|   Block 6
+# 1039|     r6_0(glval<int>) = VariableAddress[#return] : 
+# 1039|     r6_1(int)        = Constant[0]              : 
+# 1039|     m6_2(int)        = Store                    : r6_0, r6_1
+#-----|   Goto -> Block 1
+
+# 1042|   Block 7
+# 1042|     r7_0(glval<int>) = VariableAddress[#return] : 
+# 1042|     r7_1(int)        = Constant[1]              : 
+# 1042|     m7_2(int)        = Store                    : r7_0, r7_1
+#-----|   Goto -> Block 1

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

@@ -1018,4 +1018,30 @@ int ChiPhiNode(Point *p, bool which1, bool which2) {
   return p->x + p->y;
 }
 
+int UnreachableViaGoto() {
+  goto skip;
+  return 1;
+skip:
+  return 0;
+}
+
+int UnreachableIf(bool b) {
+  if (b) {
+    if (false) {
+      return 1;
+    }
+    else {
+      return 0;
+    }
+  }
+  else {
+    if (true) {
+      return 0;
+    }
+    else {
+      return 1;
+    }
+  }
+}
+
 // semmle-extractor-options: -std=c++17

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

@@ -4420,3 +4420,82 @@ ir.cpp:
 # 1005|     v6_12(void)          = ReturnValue              : r6_11, mu0_2
 # 1005|     v6_13(void)          = UnmodeledUse             : mu*
 # 1005|     v6_14(void)          = ExitFunction             : 
+
+# 1021| UnreachableViaGoto() -> int
+# 1021|   Block 0
+# 1021|     v0_0(void)       = EnterFunction            : 
+# 1021|     mu0_1(unknown)   = AliasedDefinition        : 
+# 1021|     mu0_2(unknown)   = UnmodeledDefinition      : 
+# 1022|     v0_3(void)       = NoOp                     : 
+# 1024|     v0_4(void)       = NoOp                     : 
+# 1025|     r0_5(glval<int>) = VariableAddress[#return] : 
+# 1025|     r0_6(int)        = Constant[0]              : 
+# 1025|     mu0_7(int)       = Store                    : r0_5, r0_6
+#-----|   Goto -> Block 1
+
+# 1021|   Block 1
+# 1021|     r1_0(glval<int>) = VariableAddress[#return] : 
+# 1021|     v1_1(void)       = ReturnValue              : r1_0, mu0_2
+# 1021|     v1_2(void)       = UnmodeledUse             : mu*
+# 1021|     v1_3(void)       = ExitFunction             : 
+
+# 1023|   Block 2
+# 1023|     r2_0(glval<int>) = VariableAddress[#return] : 
+# 1023|     r2_1(int)        = Constant[1]              : 
+# 1023|     mu2_2(int)       = Store                    : r2_0, r2_1
+#-----|   Goto -> Block 1
+
+# 1028| UnreachableIf(bool) -> int
+# 1028|   Block 0
+# 1028|     v0_0(void)        = EnterFunction          : 
+# 1028|     mu0_1(unknown)    = AliasedDefinition      : 
+# 1028|     mu0_2(unknown)    = UnmodeledDefinition    : 
+# 1028|     r0_3(glval<bool>) = VariableAddress[b]     : 
+# 1028|     mu0_4(bool)       = InitializeParameter[b] : r0_3
+# 1029|     r0_5(glval<bool>) = VariableAddress[b]     : 
+# 1029|     r0_6(bool)        = Load                   : r0_5, mu0_2
+# 1029|     v0_7(void)        = ConditionalBranch      : r0_6
+#-----|   False -> Block 5
+#-----|   True -> Block 2
+
+# 1028|   Block 1
+# 1028|     r1_0(glval<int>) = VariableAddress[#return] : 
+# 1028|     v1_1(void)       = ReturnValue              : r1_0, mu0_2
+# 1028|     v1_2(void)       = UnmodeledUse             : mu*
+# 1028|     v1_3(void)       = ExitFunction             : 
+
+# 1030|   Block 2
+# 1030|     r2_0(bool) = Constant[0]       : 
+# 1030|     v2_1(void) = ConditionalBranch : r2_0
+#-----|   False -> Block 4
+#-----|   True -> Block 3
+
+# 1031|   Block 3
+# 1031|     r3_0(glval<int>) = VariableAddress[#return] : 
+# 1031|     r3_1(int)        = Constant[1]              : 
+# 1031|     mu3_2(int)       = Store                    : r3_0, r3_1
+#-----|   Goto -> Block 1
+
+# 1034|   Block 4
+# 1034|     r4_0(glval<int>) = VariableAddress[#return] : 
+# 1034|     r4_1(int)        = Constant[0]              : 
+# 1034|     mu4_2(int)       = Store                    : r4_0, r4_1
+#-----|   Goto -> Block 1
+
+# 1038|   Block 5
+# 1038|     r5_0(bool) = Constant[1]       : 
+# 1038|     v5_1(void) = ConditionalBranch : r5_0
+#-----|   False -> Block 7
+#-----|   True -> Block 6
+
+# 1039|   Block 6
+# 1039|     r6_0(glval<int>) = VariableAddress[#return] : 
+# 1039|     r6_1(int)        = Constant[0]              : 
+# 1039|     mu6_2(int)       = Store                    : r6_0, r6_1
+#-----|   Goto -> Block 1
+
+# 1042|   Block 7
+# 1042|     r7_0(glval<int>) = VariableAddress[#return] : 
+# 1042|     r7_1(int)        = Constant[1]              : 
+# 1042|     mu7_2(int)       = Store                    : r7_0, r7_1
+#-----|   Goto -> Block 1

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

@@ -93,6 +93,8 @@
 | IR: TryCatch | 15 |
 | IR: UninitializedVariables | 1 |
 | IR: UnionInit | 1 |
+| IR: UnreachableIf | 8 |
+| IR: UnreachableViaGoto | 3 |
 | IR: VarArgUsage | 1 |
 | IR: VarArgs | 1 |
 | IR: VirtualMemberFunction | 1 |

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

@@ -4441,3 +4441,84 @@ ir.cpp:
 # 1005|     v6_12(void)          = ReturnValue              : r6_11, m6_10
 # 1005|     v6_13(void)          = UnmodeledUse             : mu*
 # 1005|     v6_14(void)          = ExitFunction             : 
+
+# 1021| UnreachableViaGoto() -> int
+# 1021|   Block 0
+# 1021|     v0_0(void)       = EnterFunction            : 
+# 1021|     mu0_1(unknown)   = AliasedDefinition        : 
+# 1021|     mu0_2(unknown)   = UnmodeledDefinition      : 
+# 1022|     v0_3(void)       = NoOp                     : 
+# 1024|     v0_4(void)       = NoOp                     : 
+# 1025|     r0_5(glval<int>) = VariableAddress[#return] : 
+# 1025|     r0_6(int)        = Constant[0]              : 
+# 1025|     m0_7(int)        = Store                    : r0_5, r0_6
+#-----|   Goto -> Block 1
+
+# 1021|   Block 1
+# 1021|     m1_0(int)        = Phi                      : from 0:m0_7, from 2:m2_2
+# 1021|     r1_1(glval<int>) = VariableAddress[#return] : 
+# 1021|     v1_2(void)       = ReturnValue              : r1_1, m1_0
+# 1021|     v1_3(void)       = UnmodeledUse             : mu*
+# 1021|     v1_4(void)       = ExitFunction             : 
+
+# 1023|   Block 2
+# 1023|     r2_0(glval<int>) = VariableAddress[#return] : 
+# 1023|     r2_1(int)        = Constant[1]              : 
+# 1023|     m2_2(int)        = Store                    : r2_0, r2_1
+#-----|   Goto -> Block 1
+
+# 1028| UnreachableIf(bool) -> int
+# 1028|   Block 0
+# 1028|     v0_0(void)        = EnterFunction          : 
+# 1028|     mu0_1(unknown)    = AliasedDefinition      : 
+# 1028|     mu0_2(unknown)    = UnmodeledDefinition    : 
+# 1028|     r0_3(glval<bool>) = VariableAddress[b]     : 
+# 1028|     m0_4(bool)        = InitializeParameter[b] : r0_3
+# 1029|     r0_5(glval<bool>) = VariableAddress[b]     : 
+# 1029|     r0_6(bool)        = Load                   : r0_5, m0_4
+# 1029|     v0_7(void)        = ConditionalBranch      : r0_6
+#-----|   False -> Block 5
+#-----|   True -> Block 2
+
+# 1028|   Block 1
+# 1028|     m1_0(int)        = Phi                      : from 3:m3_2, from 4:m4_2, from 6:m6_2, from 7:m7_2
+# 1028|     r1_1(glval<int>) = VariableAddress[#return] : 
+# 1028|     v1_2(void)       = ReturnValue              : r1_1, m1_0
+# 1028|     v1_3(void)       = UnmodeledUse             : mu*
+# 1028|     v1_4(void)       = ExitFunction             : 
+
+# 1030|   Block 2
+# 1030|     r2_0(bool) = Constant[0]       : 
+# 1030|     v2_1(void) = ConditionalBranch : r2_0
+#-----|   False -> Block 4
+#-----|   True -> Block 3
+
+# 1031|   Block 3
+# 1031|     r3_0(glval<int>) = VariableAddress[#return] : 
+# 1031|     r3_1(int)        = Constant[1]              : 
+# 1031|     m3_2(int)        = Store                    : r3_0, r3_1
+#-----|   Goto -> Block 1
+
+# 1034|   Block 4
+# 1034|     r4_0(glval<int>) = VariableAddress[#return] : 
+# 1034|     r4_1(int)        = Constant[0]              : 
+# 1034|     m4_2(int)        = Store                    : r4_0, r4_1
+#-----|   Goto -> Block 1
+
+# 1038|   Block 5
+# 1038|     r5_0(bool) = Constant[1]       : 
+# 1038|     v5_1(void) = ConditionalBranch : r5_0
+#-----|   False -> Block 7
+#-----|   True -> Block 6
+
+# 1039|   Block 6
+# 1039|     r6_0(glval<int>) = VariableAddress[#return] : 
+# 1039|     r6_1(int)        = Constant[0]              : 
+# 1039|     m6_2(int)        = Store                    : r6_0, r6_1
+#-----|   Goto -> Block 1
+
+# 1042|   Block 7
+# 1042|     r7_0(glval<int>) = VariableAddress[#return] : 
+# 1042|     r7_1(int)        = Constant[1]              : 
+# 1042|     m7_2(int)        = Store                    : r7_0, r7_1
+#-----|   Goto -> Block 1