Merge pull request #21457 from geoffw0/intmultlong

C++: Fix BMN issue with cpp/integer-multiplication-cast-to-long.

Author: geoffw0

cpp/ql/lib/semmle/code/cpp/Function.qll

@@ -524,6 +524,12 @@ class Function extends Declaration, ControlFlowNode, AccessHolder, @function {
       not exists(NewOrNewArrayExpr new | e = new.getAllocatorCall().getArgument(0))
     )
   }
+
+  /**
+   * Holds if this function has an ambiguous return type, meaning that zero or multiple return
+   * types for this function are present in the database (this can occur in `build-mode: none`).
+   */
+  predicate hasAmbiguousReturnType() { count(this.getType()) != 1 }
 }
 
 pragma[noinline]

cpp/ql/src/Likely Bugs/Arithmetic/IntMultToLong.ql

@@ -218,7 +218,9 @@ where
   // only report if we cannot prove that the result of the
   // multiplication will be less (resp. greater) than the
   // maximum (resp. minimum) number we can compute.
-  overflows(me, t1)
+  overflows(me, t1) and
+  // exclude cases where the expression type may not have been extracted accurately
+  not me.getParent().(Call).getTarget().hasAmbiguousReturnType()
 select me,
   "Multiplication result may overflow '" + me.getType().toString() + "' before it is converted to '"
     + me.getFullyConverted().getType().toString() + "'."

cpp/ql/src/change-notes/2026-03-11-integer-multiplication-cast-to-long.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Fixed an issue with the "Multiplication result converted to larger type" (`cpp/integer-multiplication-cast-to-long`) query causing false positive results in `build-mode: none` databases.

cpp/ql/test/query-tests/Likely Bugs/Arithmetic/IntMultToLong/Buildless.c

@@ -0,0 +1,28 @@
+// semmle-extractor-options: --expect_errors
+
+void test_float_double1(float f, double d) {
+    float r1 = f * f; // GOOD
+    float r2 = f * d; // GOOD
+    double r3 = f * f; // BAD
+    double r4 = f * d; // GOOD
+
+    float f1 = fabsf(f * f); // GOOD
+    float f2 = fabsf(f * d); // GOOD
+    double f3 = fabs(f * f); // BAD [NOT DETECTED]
+    double f4 = fabs(f * d); // GOOD
+}
+
+double fabs(double f);
+float fabsf(float f);
+
+void test_float_double2(float f, double d) {
+    float r1 = f * f; // GOOD
+    float r2 = f * d; // GOOD
+    double r3 = f * f; // BAD
+    double r4 = f * d; // GOOD
+
+    float f1 = fabsf(f * f); // GOOD
+    float f2 = fabsf(f * d); // GOOD
+    double f3 = fabs(f * f); // BAD [NOT DETECTED]
+    double f4 = fabs(f * d); // GOOD
+}

cpp/ql/test/query-tests/Likely Bugs/Arithmetic/IntMultToLong/IntMultToLong.expected

@@ -1,3 +1,5 @@
+| Buildless.c:6:17:6:21 | ... * ... | Multiplication result may overflow 'float' before it is converted to 'double'. |
+| Buildless.c:21:17:21:21 | ... * ... | Multiplication result may overflow 'float' before it is converted to 'double'. |
 | IntMultToLong.c:4:10:4:14 | ... * ... | Multiplication result may overflow 'int' before it is converted to 'long long'. |
 | IntMultToLong.c:7:16:7:20 | ... * ... | Multiplication result may overflow 'int' before it is converted to 'long long'. |
 | IntMultToLong.c:18:19:18:23 | ... * ... | Multiplication result may overflow 'float' before it is converted to 'double'. |