[llvm-bugs] [Bug 25769] New: -Wparentheses could give a smarter diagnostic if one of the operators is bitwise & or | and the operands have type `bool`

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=25769

            Bug ID: 25769
           Summary: -Wparentheses could give a smarter diagnostic if one
                    of the operators is bitwise & or | and the operands
                    have type `bool`
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: richard-llvm at metafoo.co.uk
                CC: llvm-bugs at lists.llvm.org, rtrieu at google.com
    Classification: Unclassified

Today I saw this:

tools/clang/lib/AST/ExprConstant.cpp:8866:49: warning: & has lower precedence
than <; < will be evaluated first [-Wparentheses]
         (SEK < Expr::SE_AllowUndefinedBehavior & Result.HasUndefinedBehavior);
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
tools/clang/lib/AST/ExprConstant.cpp:8866:49: note: place parentheses around
the '<' expression to silence this warning
         (SEK < Expr::SE_AllowUndefinedBehavior & Result.HasUndefinedBehavior);
                                                ^
          (                                    )
tools/clang/lib/AST/ExprConstant.cpp:8866:49: note: place parentheses around
the & expression to evaluate it first   
         (SEK < Expr::SE_AllowUndefinedBehavior & Result.HasUndefinedBehavior);
                                                ^
                (                                                            )

This is pretty good, but we could be smarter here: we have a bitwise & operator
where both operands are of type 'bool'. In that case, we should guess that the
user did actually mean an 'and' operator, and suggest changing it to '&&'
(unless the RHS has side-effects, in which case maybe suggesting parens is the
right thing).

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