[clang-tidy] cppcoreguidelines-pro-bounds-pointer-arithmetic: ignore generated pointer arithmetic

[mgehre]

Summary

Inside a range-based for-loop over an array, the compiler
generates pointer arithmetic (end = array + size). Don't flag this.

[aaron.ballman]

clang-tidy/cppcoreguidelines/ProBoundsPointerArithmeticCheck.cpp

19 ↗

(On Diff #39957)

This same code exists in ProBoundsArrayToPointerDecayCheck.cpp and should not be duplicated. I kind of wonder whether this belongs in clangTidyUtils, or in the AST matchers. I think for right now, clangTidyUtils because they still seem a little niche.

[alexfh]

It may be more effective to filter out expressions that operate on implicit variables, e.g. by adding this constraint to the binaryOperator matcher:

unless(hasLHS(ignoringImpCasts(declRefExpr(to(isImplicit())))))

(maybe also for RHS).

The benefit of this would be that it doesn't use hasAncestor/hasDescendant which can be rather expensive.

[mgehre]

Simplified with Alex suggestion. Thanks!

[alexfh]

Sorry for the delay, I was sick and didn't read mail.

Looks good with a nit. Thanks for the fix!

clang-tidy/cppcoreguidelines/ProBoundsPointerArithmeticCheck.cpp

28 ↗

(On Diff #40448)

nit: Does this still fit to 80 characters? I mean, clang-format, please ;)

clang-tools-extra/trunk/clang-tidy/cppcoreguidelines/ProBoundsPointerArithmeticCheck.cpp

 namespace tidy {
 
 void ProBoundsPointerArithmeticCheck::registerMatchers(MatchFinder *Finder) {
   if (!getLangOpts().CPlusPlus)
     return;
 
   // Flag all operators +, -, +=, -=, ++, -- that result in a pointer
   Finder->addMatcher(
-      binaryOperator(anyOf(hasOperatorName("+"), hasOperatorName("-"),
-                           hasOperatorName("+="), hasOperatorName("-=")),
-                     hasType(pointerType()))
+      binaryOperator(
+          anyOf(hasOperatorName("+"), hasOperatorName("-"),
+          hasType(pointerType()),
+          unless(hasLHS(ignoringImpCasts(declRefExpr(to(isImplicit()))))))
           .bind("expr"),
       this);
 
   Finder->addMatcher(
       unaryOperator(anyOf(hasOperatorName("++"), hasOperatorName("--")),
                     hasType(pointerType()))
           .bind("expr"),
       this);
 
   // Array subscript on a pointer (not an array) is also pointer arithmetic
   Finder->addMatcher(
-      arraySubscriptExpr(hasBase(ignoringImpCasts(anyOf(hasType(pointerType()),
-                                                        hasType(decayedType(hasDecayedType(pointerType())))))))
+      arraySubscriptExpr(
+          hasBase(ignoringImpCasts(
+              anyOf(hasType(pointerType()),
           .bind("expr"),
       this);
 }
 
 void
 ProBoundsPointerArithmeticCheck::check(const MatchFinder::MatchResult &Result) {
   const auto *MatchedExpr = Result.Nodes.getNodeAs<Expr>("expr");
 
   diag(MatchedExpr->getExprLoc(), "do not use pointer arithmetic");
 }
 
 } // namespace tidy
 } // namespace clang

clang-tools-extra/trunk/test/clang-tidy/cppcoreguidelines-pro-bounds-pointer-arithmetic.cpp

void okay() {
   i--;
   --i;
   i += 1;
   i -= 1;
   i = j + 1;
   i = j - 1;
 
   auto diff = p - q; // OK, result is arithmetic
+
+  for(int ii : a) ; // OK, pointer arithmetic generated by compiler
 }