C++: restrict global variable IR generation

Author: Robert Marsh

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/IRConstruction.qll

@@ -37,7 +37,14 @@ module Raw {
   predicate functionHasIR(Function func) { exists(getTranslatedFunction(func)) }
 
   cached
-  predicate varHasIRFunc(GlobalOrNamespaceVariable var) { any() } // TODO: restrict?
+  predicate varHasIRFunc(GlobalOrNamespaceVariable var) {
+    var.hasInitializer() and
+    (
+      not var.getType().isDeeplyConst()
+      or
+      var.getInitializer().getExpr() instanceof StringLiteral
+    )
+  }
 
   cached
   predicate hasInstruction(TranslatedElement element, InstructionTag tag) {

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedElement.qll

@@ -119,7 +119,7 @@ private predicate ignoreExprOnly(Expr expr) {
   exists(NewOrNewArrayExpr new | expr = new.getAllocatorCall().getArgument(0))
   or
   not translateFunction(expr.getEnclosingFunction()) and
-  not expr.getEnclosingVariable() instanceof GlobalOrNamespaceVariable
+  not Raw::varHasIRFunc(expr.getEnclosingVariable())
   or
   // We do not yet translate destructors properly, so for now we ignore the
   // destructor call. We do, however, translate the expression being
@@ -665,7 +665,7 @@ newtype TTranslatedElement =
   } or
   // The side effect that initializes newly-allocated memory.
   TTranslatedAllocationSideEffect(AllocationExpr expr) { not ignoreSideEffects(expr) } or
-  TTranslatedGlobalOrNamespaceVarInit(GlobalOrNamespaceVariable var) { var.hasInitializer() }
+  TTranslatedGlobalOrNamespaceVarInit(GlobalOrNamespaceVariable var) { Raw::varHasIRFunc(var) }
 
 /**
  * Gets the index of the first explicitly initialized element in `initList`

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

@@ -8228,11 +8228,6 @@
 | ir.cpp:1759:16:1759:16 | ChiPartial | partial:m1759_5 |
 | ir.cpp:1759:16:1759:16 | ChiTotal | total:m1759_2 |
 | ir.cpp:1759:16:1759:16 | StoreValue | r1759_4 |
-| ir.cpp:1761:11:1761:18 | Address | &:r1761_3 |
-| ir.cpp:1761:11:1761:18 | SideEffect | ~m1761_6 |
-| ir.cpp:1761:22:1761:22 | ChiPartial | partial:m1761_5 |
-| ir.cpp:1761:22:1761:22 | ChiTotal | total:m1761_2 |
-| ir.cpp:1761:22:1761:22 | StoreValue | r1761_4 |
 | ir.cpp:1763:18:1763:25 | Address | &:r1763_3 |
 | ir.cpp:1763:18:1763:25 | Arg(this) | this:r1763_3 |
 | ir.cpp:1763:18:1763:25 | SideEffect | ~m1763_10 |

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

@@ -9442,17 +9442,6 @@ ir.cpp:
 # 1759|     v1759_7(void)       = AliasedUse                : ~m?
 # 1759|     v1759_8(void)       = ExitFunction              : 
 
-# 1761| int const global_3
-# 1761|   Block 0
-# 1761|     v1761_1(void)       = EnterFunction             : 
-# 1761|     mu1761_2(unknown)   = AliasedDefinition         : 
-# 1761|     r1761_3(glval<int>) = VariableAddress[global_3] : 
-# 1761|     r1761_4(int)        = Constant[2]               : 
-# 1761|     mu1761_5(int)       = Store[global_3]           : &:r1761_3, r1761_4
-# 1761|     v1761_6(void)       = ReturnVoid                : 
-# 1761|     v1761_7(void)       = AliasedUse                : ~m?
-# 1761|     v1761_8(void)       = ExitFunction              : 
-
 # 1763| constructor_only global_4
 # 1763|   Block 0
 # 1763|     v1763_1(void)                    = EnterFunction                     : 

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

@@ -1234,8 +1234,6 @@ ssa.cpp:
 #  268|     v268_14(void)          = AliasedUse                         : ~m269_7
 #  268|     v268_15(void)          = ExitFunction                       : 
 
-#  274| Point* pp
-
 #  275| void EscapedButNotConflated(bool, Point, int)
 #  275|   Block 0
 #  275|     v275_1(void)           = EnterFunction           : 

cpp/ql/test/library-tests/ir/ssa/aliased_ssa_ir_unsound.expected

@@ -1229,8 +1229,6 @@ ssa.cpp:
 #  268|     v268_14(void)          = AliasedUse                         : ~m269_7
 #  268|     v268_15(void)          = ExitFunction                       : 
 
-#  274| Point* pp
-
 #  275| void EscapedButNotConflated(bool, Point, int)
 #  275|   Block 0
 #  275|     v275_1(void)           = EnterFunction           : 

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

@@ -1140,8 +1140,6 @@ ssa.cpp:
 #  268|     v268_13(void)          = AliasedUse                         : ~m?
 #  268|     v268_14(void)          = ExitFunction                       : 
 
-#  274| Point* pp
-
 #  275| void EscapedButNotConflated(bool, Point, int)
 #  275|   Block 0
 #  275|     v275_1(void)           = EnterFunction           : 

cpp/ql/test/library-tests/ir/ssa/unaliased_ssa_ir_unsound.expected

@@ -1140,8 +1140,6 @@ ssa.cpp:
 #  268|     v268_13(void)          = AliasedUse                         : ~m?
 #  268|     v268_14(void)          = ExitFunction                       : 
 
-#  274| Point* pp
-
 #  275| void EscapedButNotConflated(bool, Point, int)
 #  275|   Block 0
 #  275|     v275_1(void)           = EnterFunction           : 

cpp/ql/test/library-tests/valuenumbering/GlobalValueNumbering/ir_gvn.expected

@@ -941,10 +941,6 @@ test.cpp:
 #  124|     v124_13(void)      = AliasedUse                : m124_3
 #  124|     v124_14(void)      = ExitFunction              : 
 
-#  132| A* global_a
-
-#  133| int global_n
-
 #  135| void test_read_global_same()
 #  135|   Block 0
 #  135|     v135_1(void)       = EnterFunction             :