[PATCH] check for Incorrect logic in operator

[Richard Trieu]

+    const IntegerLiteral *Literal1 =
+            dyn_cast<IntegerLiteral>(LHS->getRHS()->IgnoreParens());
Note that this won't work on negative values.

+    Literal1->EvaluateAsInt(L1,*Context);
+    Literal2->EvaluateAsInt(L2,*Context);
+
+    if (!L1 || !L2)
+      return TryResult();
if (!Literal1->EvaluateAsInt(L1, *Context) || Literal2->EvaluateAsInt(L2,
*Context))
  return TryResult();

+    const llvm::APSInt MinValue =
+        llvm::APSInt::getMinValue(L1.getBitWidth(), L1.isUnsigned());
+    const llvm::APSInt MaxValue =
+        llvm::APSInt::getMaxValue(L1.getBitWidth(), L1.isUnsigned());
Move these into the array below.

+    llvm::APSInt I1 = llvm::APSInt(llvm::APInt(L1.getBitWidth(), 1),
+        L1.isUnsigned());
Don't need this.

+      // Value between Value1 and Value2
+      ((L1 < L2) ? L1 : L2) + I1,
Use the APSInt ++operator.

+    if(AlwaysTrue || AlwaysFalse) {
+      if(BuildOpts.Observer)
Add space between the if and the parentheses.

+  void compareAlwaysTrue(const BinaryOperator* B, bool isAlwaysTrue) {
BinaryOperator *B

+    if (LHS)
+      if (LHS->getLHS()->getExprLoc().isMacroID() ||
+          LHS->getRHS()->getExprLoc().isMacroID())
+            return;
+    if (RHS)
+      if (RHS->getLHS()->getExprLoc().isMacroID() ||
+          RHS->getRHS()->getExprLoc().isMacroID())
+            return;
if (!LHS || !RHS) first, then the two macro checks afterwards.

+    SourceRange DiagRange(B->getLHS()->getLocStart(),
B->getRHS()->getLocEnd());
+    S.Diag(B->getExprLoc(), diag::warn_operator_always_true_comparison)
+        << DiagRange << isAlwaysTrue;
Use B->getSourceRange() instead of creating a new SourceRange.

Same changes to compareBoolWithInt

-    if (!isTemplateInstantiation)
+    if (!isTemplateInstantiation) {
+      LogicalErrorsHandler Leh(S);
+      AC.getCFGBuildOptions().Observer = &Leh;
       CheckUnreachable(S, AC);
+    }
This forces your warning to be dependent on a different and unrelated
function.  Instead, use:

if (Diags.getDiagnosticLevel(diag::warn_operator_always_true_comparison,
D->getLocStart()) {
  LogicalErrorsHandler LEH(S);
  AC.getCFGBuildOptions().Observer = &LEH;
  AC.getCFG();
}

Place this before the "Emit delayed diagnostics." comment.  CFG builds are
cached, so the observer must be attached to the first run of getCFG.  It
would also be a good idea to have a reset observer function after just in
case the CFG is rebuilt later.

+def warn_operator_always_true_comparison : Warning<
+  "overlapping comparisons always evaluate to %select{false|true}0">,
+  InGroup<TautologicalCompareOperator>;
+def warn_bool_and_int_comparison : Warning<
+  "comparison of a boolean expression with an integer other than 0 or 1">,
+  InGroup<TautologicalCompareOperator>;
Add DefaultIgnore to these warnings.

def TautologicalOutOfRangeCompare :
DiagGroup<"tautological-constant-out-of-range-compare">;
def TautologicalCompare : DiagGroup<"tautological-compare",
                                     [TautologicalOutOfRangeCompare]>;
+def TautologicalCompareOperator :
DiagGroup<"tautological-compare-operator",
+                                    [TautologicalCompare]>;

TautologicalCompareOperator should be a subgroup of TautologicalCompare,
not the other way around


+// RUN: %clang_cc1 -fsyntax-only -verify -Wunreachable-code %s
Remove -Wunreachable-code and replace with -Wtautological-compare-operator
in both tests.
Add some cases with zero to warn-overlap.c

On Fri, Feb 21, 2014 at 5:48 AM, Anders Rönnholm <
Anders.Ronnholm at evidente.se> wrote:

> Pinging this patch.
>
> > -----Original Message-----
> > From: Anders Rönnholm
> > Sent: den 20 december 2013 13:35
> > To: Richard Smith; Richard Trieu
> > Cc: cfe-commits at cs.uiuc.edu
> > Subject: Re: [PATCH] check for Incorrect logic in operator
> >
> > Tanks for your comments. New patch attached.
> >
> > -- We can have some warnings in a group on by default and some off by
> > default, but this does suggest that we'd want a new warning subgroup for
> > this warning.
> > Do you want a new subgroup and how do you create one? I have moved it
> > back to tautological and made a what i think is a subgroup.
>
You have made -Wtautogical-compare a subgroup of your warning.  Switch it
so that using -Wtautological-compare will also turn on your warning.

> >
> > -- Instead of looking for an integer literal, see if the expression can
> be
> > evaluated, and use that as the constant value.  This will allow things
> like 1+2
> > and -1.
> > I will skip this because it will also generate false positives when it's
> x+1 and
> > can be evaluated.
>
What false positives are you seeing?  I would think that negative numbers
should be checked with this warning as well.

> >
> > --Also, does your patch cause the unreachable-code warning to trigger in
> > more cases now?
> > I have tested it on llvm and the patch did not trigger more
> unreachable-code
> > warnings.
> >
> > -- What is going on here?
> > Comments in code, also slight refactoring Basicly it checks whether the
> > expression is always true/false by checking following scenarios.
> >     x is less than the smallest literal.
> >     x is equal to the smallest literal.
> >     x is between smallest and largest literal.
> >     x is equal to the largest literal.
> >     x is greater than largest literal.
> >
> > For && both RHS and LHS needs to be true or false in every scenario for
> it to
> > be regarded always true/false.
> > For || either RHS and LHS needs to be true or false in every scenario
> for it to
> > be regarded always true/false.
>
This refactoring makes the logic much clearer now.

> >
> > -- What's the plan with CFGCallBack?  New methods added as needed for
> > each new warning?  Does the CFGBuilder need to support multiple
> > CFGCallBack's at once?
> > Yes new methods would have to be added. No i don't see a reason for the
> > need of supporting multiple CFGCallBack's at once.
> >
> > //Anders
> >
> >
> >
> .....................................................................................................................
> > ..
> > Anders Rönnholm Senior Engineer
> > Evidente ES East AB  Warfvinges väg 34  SE-112 51 Stockholm  Sweden
> >
> > Mobile:                    +46 (0)70 912 42 54
> > E-mail:                    Anders.Ronnholm at evidente.se
> >
> > www.evidente.se
> >
> > ________________________________________
>
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