C++: Suppress pointless compare in template inst.

jbj · jbj · commit 364c9a69614d · 2018-10-03T14:48:11.000+02:00
It still runs on uninstantiated templates because its underlying
libraries do. It's not clear whether that leads to other false
positives, but that's independent of the change I'm making here.
diff --git a/cpp/ql/src/Likely Bugs/Arithmetic/PointlessComparison.ql b/cpp/ql/src/Likely Bugs/Arithmetic/PointlessComparison.ql
@@ -22,13 +22,15 @@ import UnsignedGEZero
 // #define PRINTMSG(val,msg) { if (val >= PRINTLEVEL) printf(msg); }
 //
 // So to reduce the number of false positives, we do not report a result if
-// the comparison is in a macro expansion.
+// the comparison is in a macro expansion. Similarly for template
+// instantiations.
 from
   ComparisonOperation cmp, SmallSide ss,
   float left, float right, boolean value,
   string reason
 where
   not cmp.isInMacroExpansion() and
+  not cmp.isFromTemplateInstantiation(_) and
   reachablePointlessComparison(cmp, left, right, value, ss) and
 
   // a comparison between an enum and zero is always valid because whether
diff --git a/cpp/ql/test/query-tests/Likely Bugs/Arithmetic/PointlessComparison/PointlessComparison.expected b/cpp/ql/test/query-tests/Likely Bugs/Arithmetic/PointlessComparison/PointlessComparison.expected
@@ -32,7 +32,4 @@
 | PointlessComparison.c:129:12:129:16 | ... > ... | Comparison is always false because a <= 3. |
 | PointlessComparison.c:197:7:197:11 | ... < ... | Comparison is always false because x >= 0. |
 | RegressionTests.cpp:57:7:57:22 | ... <= ... | Comparison is always true because * ... <= 4294967295. |
-| Templates.cpp:3:10:3:24 | ... <= ... | Comparison is always true because param <= 32767. |
-| Templates.cpp:9:10:9:24 | ... <= ... | Comparison is always true because local <= 32767. |
-| Templates.cpp:9:10:9:24 | ... <= ... | Comparison is always true because local <= 32767. |
 | Templates.cpp:9:10:9:24 | ... <= ... | Comparison is always true because local <= 32767. |
diff --git a/cpp/ql/test/query-tests/Likely Bugs/Arithmetic/PointlessComparison/Templates.cpp b/cpp/ql/test/query-tests/Likely Bugs/Arithmetic/PointlessComparison/Templates.cpp
@@ -1,6 +1,6 @@
 template<typename T>
 bool sometimesPointless(T param) {
-  return param <= 0xFFFF; // GOOD (FALSE POSITIVE: hypothetical instantiations are okay)
+  return param <= 0xFFFF; // GOOD (hypothetical instantiations are okay)
 }
 
 template<typename T>

Original file line number	Diff line number	Diff line change
`@@ -1,6 +1,6 @@`
`1`	`1`	`template<typename T>`
`2`	`2`	`bool sometimesPointless(T param) {`
`3`		`- return param <= 0xFFFF; // GOOD (FALSE POSITIVE: hypothetical instantiations are okay)`
	`3`	`+ return param <= 0xFFFF; // GOOD (hypothetical instantiations are okay)`
`4`	`4`	`}`
`5`	`5`
`6`	`6`	`template<typename T>`