Merge pull request #14115 from MathiasVP/fix-incorrect-load-of-constant

C++: Don't generate `Load`s for constant expressions

Author: MathiasVP

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

@@ -415,7 +415,9 @@ predicate hasTranslatedLoad(Expr expr) {
   not ignoreExpr(expr) and
   not isNativeCondition(expr) and
   not isFlexibleCondition(expr) and
-  not ignoreLoad(expr)
+  not ignoreLoad(expr) and
+  // don't insert a load since we'll just substitute the constant value.
+  not isIRConstant(expr)
 }
 
 /**

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

@@ -15716,6 +15716,30 @@ ir.cpp:
 # 2065|               Type = [PointerType] Derived2 *
 # 2065|               ValueCategory = prvalue(load)
 # 2066|     getStmt(6): [ReturnStmt] return ...
+# 2068| [TopLevelFunction] void test_constant_folding_use(int)
+# 2068|   <params>: 
+# 2068|     getParameter(0): [Parameter] (unnamed parameter 0)
+# 2068|         Type = [IntType] int
+# 2070| [TopLevelFunction] void test_constant_folding()
+# 2070|   <params>: 
+# 2070|   getEntryPoint(): [BlockStmt] { ... }
+# 2071|     getStmt(0): [DeclStmt] declaration
+# 2071|       getDeclarationEntry(0): [VariableDeclarationEntry] definition of x
+# 2071|           Type = [SpecifiedType] const int
+# 2071|         getVariable().getInitializer(): [Initializer] initializer for x
+# 2071|           getExpr(): [Literal] 116
+# 2071|               Type = [IntType] int
+# 2071|               Value = [Literal] 116
+# 2071|               ValueCategory = prvalue
+# 2072|     getStmt(1): [ExprStmt] ExprStmt
+# 2072|       getExpr(): [FunctionCall] call to test_constant_folding_use
+# 2072|           Type = [VoidType] void
+# 2072|           ValueCategory = prvalue
+# 2072|         getArgument(0): [VariableAccess] x
+# 2072|             Type = [IntType] int
+# 2072|             Value = [VariableAccess] 116
+# 2072|             ValueCategory = prvalue(load)
+# 2073|     getStmt(2): [ReturnStmt] return ...
 perf-regression.cpp:
 #    4| [CopyAssignmentOperator] Big& Big::operator=(Big const&)
 #    4|   <params>: 

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

@@ -2065,5 +2065,11 @@ int virtual_delete()
     delete d;
 }
 
+void test_constant_folding_use(int);
+
+void test_constant_folding() {
+  const int x = 116;
+  test_constant_folding_use(x);
+}
 
 // semmle-extractor-options: -std=c++17 --clang

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

@@ -9796,6 +9796,16 @@
 | ir.cpp:2065:12:2065:12 | Address | &:r2065_2 |
 | ir.cpp:2065:12:2065:12 | Arg(0) | 0:r2065_3 |
 | ir.cpp:2065:12:2065:12 | Load | m2064_15 |
+| ir.cpp:2070:6:2070:26 | ChiPartial | partial:m2070_3 |
+| ir.cpp:2070:6:2070:26 | ChiTotal | total:m2070_2 |
+| ir.cpp:2070:6:2070:26 | SideEffect | ~m2072_5 |
+| ir.cpp:2071:13:2071:13 | Address | &:r2071_1 |
+| ir.cpp:2071:16:2071:19 | StoreValue | r2071_2 |
+| ir.cpp:2072:3:2072:27 | CallTarget | func:r2072_1 |
+| ir.cpp:2072:3:2072:27 | ChiPartial | partial:m2072_4 |
+| ir.cpp:2072:3:2072:27 | ChiTotal | total:m2070_4 |
+| ir.cpp:2072:3:2072:27 | SideEffect | ~m2070_4 |
+| ir.cpp:2072:29:2072:29 | Arg(0) | 0:r2072_2 |
 | perf-regression.cpp:6:3:6:5 | Address | &:r6_5 |
 | perf-regression.cpp:6:3:6:5 | Address | &:r6_5 |
 | perf-regression.cpp:6:3:6:5 | Address | &:r6_7 |

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

@@ -11303,6 +11303,23 @@ ir.cpp:
 # 2056|     v2056_6(void)       = AliasedUse               : ~m?
 # 2056|     v2056_7(void)       = ExitFunction             : 
 
+# 2070| void test_constant_folding()
+# 2070|   Block 0
+# 2070|     v2070_1(void)           = EnterFunction                              : 
+# 2070|     mu2070_2(unknown)       = AliasedDefinition                          : 
+# 2070|     mu2070_3(unknown)       = InitializeNonLocal                         : 
+# 2071|     r2071_1(glval<int>)     = VariableAddress[x]                         : 
+# 2071|     r2071_2(int)            = Constant[116]                              : 
+# 2071|     mu2071_3(int)           = Store[x]                                   : &:r2071_1, r2071_2
+# 2072|     r2072_1(glval<unknown>) = FunctionAddress[test_constant_folding_use] : 
+# 2072|     r2072_2(int)            = Constant[116]                              : 
+# 2072|     v2072_3(void)           = Call[test_constant_folding_use]            : func:r2072_1, 0:r2072_2
+# 2072|     mu2072_4(unknown)       = ^CallSideEffect                            : ~m?
+# 2073|     v2073_1(void)           = NoOp                                       : 
+# 2070|     v2070_4(void)           = ReturnVoid                                 : 
+# 2070|     v2070_5(void)           = AliasedUse                                 : ~m?
+# 2070|     v2070_6(void)           = ExitFunction                               : 
+
 perf-regression.cpp:
 #    6| void Big::Big()
 #    6|   Block 0

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

@@ -10,7 +10,7 @@ void m(int i, bool cond, int x, int y) {
 
     int seven = 7;
     if (mul % c2 == seven) {
-        mod(mul); // congruent 3 mod 42, 7 mod 43
+        mod(mul); // $ mod=0,3,42
     }
 
     int j = cond
@@ -19,13 +19,11 @@ void m(int i, bool cond, int x, int y) {
     mod(j); // $ mod=0,3,4
 
     if (x % c1 == 3 && y % c1 == 7) {
-        // Need implies_v2
-        mod(x + y); // $ MISSING: 0,10,42
+        mod(x + y); // $ mod=0,10,42
     }
 
     if (x % c1 == 3 && y % c1 == 7) {
-        // Need implies_v2
-        mod(x - y); // $ MISSING: mod=0,38,42
+        mod(x - y); // $ mod=0,38,42
     }
 
     if (cond) {

cpp/ql/test/library-tests/ir/range-analysis/SimpleRangeAnalysis_tests.cpp

@@ -1008,12 +1008,12 @@ void test(int x) {
 
 void test_overflow() {
   const int x = 2147483647; // 2^31-1
-  range(x);
+  range(x); // $ range===2147483647
   const int y = 256;
-  range(y);
+  range(y); // $ range===256
   if ((x + y) <= 512) {
-    range(x);
-    range(y);
+    range(x); // $ range===2147483647
+    range(y); // $ range===256
     range(x + y); // $ range===-2147483393
   }
 }