[PATCH] D66014: [analyzer] Avoid unnecessary enum range check on LValueToRValue casts

[Artem Dergachev via Phabricator via cfe-commits]

NoQ added inline comments.


================
Comment at: clang/lib/StaticAnalyzer/Checkers/EnumCastOutOfRangeChecker.cpp:94-98
+  // If cast is implicit LValueToRValue, no conversion is taking place,
+  // and therefore no range check is needed.  Don't analyze further.
+  if (CE->getCastKind() == CK_LValueToRValue)
+    return;
+
----------------
If you look at the list of cast kinds, you'll be shocked to see ridiculously weird cornercases. Even though lvalue-to-rvalue cast definitely stands out (because it's the only one that has very little to do with actual casting), i'd still be much more comfortable if we *whitelist* the casts that we check, rather than blacklist them.

Can you take a look at the list and find which casts are we actually talking about and hardcode them here?


================
Comment at: clang/test/Analysis/enum-cast-out-of-range.c:27-34
+enum unscoped_unspecified_t unused;
+void unusedExpr() {
+    // following line is not something that EnumCastOutOfRangeChecker should evaluate.  checker should either ignore this line
+    // or process it without producing any warnings.  However, compilation will (and should) still generate a warning having 
+    // nothing to do with this checker.
+    unused; // expected-warning {{expression result unused}}
+}
----------------
I guess this covers D33672#1537287!

That said, there's one thing about this test that i don't understand. Why does this AST contain an implicit lvalue-to-rvalue cast at all? This looks like a (most likely otherwise harmless) bug in the AST; if i understand correctly, this should be a freestanding `DeclRefExpr`.


Repository:
  rC Clang

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D66014/new/

https://reviews.llvm.org/D66014