Re: [PATCH] c/c++: new warning: -Wxor-used-as-pow [PR90885]
On Tue, 2022-08-30 at 16:40 -0400, Marek Polacek wrote: > This looks good to me, one thing though: > > On Thu, Aug 11, 2022 at 09:38:12PM -0400, David Malcolm via Gcc- > patches wrote: > > --- a/gcc/c-family/c.opt > > +++ b/gcc/c-family/c.opt > > @@ -1439,6 +1439,10 @@ Wwrite-strings > > C ObjC C++ ObjC++ Var(warn_write_strings) Warning > > In C++, nonzero means warn about deprecated conversion from string > > literals to 'char *'. In C, similar warning, except that the > > conversion is of course not deprecated by the ISO C standard. > > > > +Wxor-used-as-pow > > +C C++ Common Var(warn_xor_used_as_pow) Warning Init(1) > > This doesn't include ObjC/ObjC++, but... I added ObjC/ObjC++ (and dropped Common), and retested it (and tested it with -xobjective-c and -xobjective-c++); I've pushed it to trunk as r13-2386-gbedfca647a9e9c. Thanks Dave
Re: [PATCH] c/c++: new warning: -Wxor-used-as-pow [PR90885]
This looks good to me, one thing though:
On Thu, Aug 11, 2022 at 09:38:12PM -0400, David Malcolm via Gcc-patches wrote:
> --- a/gcc/c-family/c.opt
> +++ b/gcc/c-family/c.opt
> @@ -1439,6 +1439,10 @@ Wwrite-strings
> C ObjC C++ ObjC++ Var(warn_write_strings) Warning
> In C++, nonzero means warn about deprecated conversion from string literals
> to 'char *'. In C, similar warning, except that the conversion is of course
> not deprecated by the ISO C standard.
>
> +Wxor-used-as-pow
> +C C++ Common Var(warn_xor_used_as_pow) Warning Init(1)
This doesn't include ObjC/ObjC++, but...
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -414,6 +414,7 @@ Objective-C and Objective-C++ Dialects}.
> -Wvector-operation-performance @gol
> -Wvla -Wvla-larger-than=@var{byte-size} -Wno-vla-larger-than @gol
> -Wvolatile-register-var -Wwrite-strings @gol
> +-Wxor-used-as-pow @gol
> -Wzero-length-bounds}
>
> @item Static Analyzer Options
> @@ -9661,6 +9662,20 @@ modifier does not inhibit all optimizations that may
> eliminate reads
> and/or writes to register variables. This warning is enabled by
> @option{-Wall}.
>
> +@item -Wxor-used-as-pow @r{(C, C++, Objective-C and Objective-C++ only)}
...here it includes Objective-C and Objective-C++.
Marek
Re: [PATCH] c/c++: new warning: -Wxor-used-as-pow [PR90885]
On 8/11/22 21:38, David Malcolm via Gcc-patches wrote: PR c/90885 notes various places in real-world code where people have written C/C++ code that uses ^ (exclusive or) where presumbably they meant exponentiation. For example https://codesearch.isocpp.org/cgi-bin/cgi_ppsearch?q=2%5E32=Search currently finds 11 places using "2^32", and all of them appear to be places where the user means 2 to the power of 32, rather than 2 exclusive-orred with 32 (which is 34). This patch adds a new -Wxor-used-as-pow warning to the C and C++ frontends to complain about ^ when the left-hand side is the decimal constant 2 or the decimal constant 10. This is the same name as the corresponding clang warning: https://clang.llvm.org/docs/DiagnosticsReference.html#wxor-used-as-pow As per the clang warning, the warning suggests converting the left-hand side to a hexadecimal constant if you really mean xor, which suppresses the warning (and this patch implements a fix-it hint for that, whereas the clang implementation only has a fix-it hint for the initial suggestion of exponentiation). I initially tried implementing this without checking for decimals, but this version had lots of false positives. Checking for decimals requires extending the lexer to capture whether or not a CPP_NUMBER token was decimal. I added a new DECIMAL_INT flag to cpplib.h for this. Unfortunately, c_token and cp_tokens both have only an unsigned char for their flags (as captured by c_lex_with_flags), whereas this would add the 12th flag to cpp_tokens. Of the first 8 flags, all but BOL are used in the C or C++ frontends, but BOL is not, so I moved that to a higher position, using its old value for the new DECIMAL_INT flag, so that it is representable within an unsigned char. Example output: demo.c:5:13: warning: result of '2^8' is 10; did you mean '1 << 8' (256)? [-Wxor-used-as-pow] 5 | int t2_8 = 2^8; | ^ |-- |1<< demo.c:5:12: note: you can silence this warning by using a hexadecimal constant (0x2 rather than 2) 5 | int t2_8 = 2^8; |^ |0x2 demo.c:21:15: warning: result of '10^6' is 12; did you mean '1e6'? [-Wxor-used-as-pow] 21 | int t10_6 = 10^6; | ^ | --- | 1e demo.c:21:13: note: you can silence this warning by using a hexadecimal constant (0xa rather than 10) 21 | int t10_6 = 10^6; | ^~ | 0xa Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu. OK for trunk? Looks good to me, but a C maintainer should sign off on the C front-end changes. Thanks Dave gcc/c-family/ChangeLog: PR c/90885 * c-common.h (check_for_xor_used_as_pow): New decl. * c-lex.cc (c_lex_with_flags): Add DECIMAL_INT to flags as appropriate. * c-warn.cc (check_for_xor_used_as_pow): New. * c.opt (Wxor-used-as-pow): New. gcc/c/ChangeLog: PR c/90885 * c-parser.cc (c_parser_string_literal): Clear ret.m_decimal. (c_parser_expr_no_commas): Likewise. (c_parser_conditional_expression): Likewise. (c_parser_binary_expression): Clear m_decimal when popping the stack. (c_parser_unary_expression): Clear ret.m_decimal. (c_parser_has_attribute_expression): Likewise for result. (c_parser_predefined_identifier): Likewise for expr. (c_parser_postfix_expression): Likewise for expr. Set expr.m_decimal when handling a CPP_NUMBER that was a decimal token. * c-tree.h (c_expr::m_decimal): New bitfield. * c-typeck.cc (parser_build_binary_op): Clear result.m_decimal. (parser_build_binary_op): Call check_for_xor_used_as_pow. gcc/cp/ChangeLog: PR c/90885 * cp-tree.h (class cp_expr): Add bitfield m_decimal. Clear it in existing ctors. Add ctor that allows specifying its value. (cp_expr::decimal_p): New accessor. * parser.cc (cp_parser_expression_stack_entry::flags): New field. (cp_parser_primary_expression): Set m_decimal of cp_expr when handling numbers. (cp_parser_binary_expression): Extract flags from token when populating stack. Call check_for_xor_used_as_pow. gcc/ChangeLog: PR c/90885 * doc/invoke.texi (Warning Options): Add -Wxor-used-as-pow. gcc/testsuite/ChangeLog: PR c/90885 * c-c++-common/Wxor-used-as-pow-1.c: New test. * c-c++-common/Wxor-used-as-pow-fixits.c: New test. * g++.dg/parse/expr3.C: Convert 2 to 0x2 to suppress -Wxor-used-as-pow. * g++.dg/warn/Wparentheses-10.C: Likewise. * g++.dg/warn/Wparentheses-18.C: Likewise. * g++.dg/warn/Wparentheses-19.C: Likewise. * g++.dg/warn/Wparentheses-9.C: Likewise. * g++.dg/warn/Wxor-used-as-pow-named-op.C: New test. * gcc.dg/Wparentheses-6.c: Convert 2 to 0x2 to suppress
[PATCH] c/c++: new warning: -Wxor-used-as-pow [PR90885]
PR c/90885 notes various places in real-world code where people have written C/C++ code that uses ^ (exclusive or) where presumbably they meant exponentiation. For example https://codesearch.isocpp.org/cgi-bin/cgi_ppsearch?q=2%5E32=Search currently finds 11 places using "2^32", and all of them appear to be places where the user means 2 to the power of 32, rather than 2 exclusive-orred with 32 (which is 34). This patch adds a new -Wxor-used-as-pow warning to the C and C++ frontends to complain about ^ when the left-hand side is the decimal constant 2 or the decimal constant 10. This is the same name as the corresponding clang warning: https://clang.llvm.org/docs/DiagnosticsReference.html#wxor-used-as-pow As per the clang warning, the warning suggests converting the left-hand side to a hexadecimal constant if you really mean xor, which suppresses the warning (and this patch implements a fix-it hint for that, whereas the clang implementation only has a fix-it hint for the initial suggestion of exponentiation). I initially tried implementing this without checking for decimals, but this version had lots of false positives. Checking for decimals requires extending the lexer to capture whether or not a CPP_NUMBER token was decimal. I added a new DECIMAL_INT flag to cpplib.h for this. Unfortunately, c_token and cp_tokens both have only an unsigned char for their flags (as captured by c_lex_with_flags), whereas this would add the 12th flag to cpp_tokens. Of the first 8 flags, all but BOL are used in the C or C++ frontends, but BOL is not, so I moved that to a higher position, using its old value for the new DECIMAL_INT flag, so that it is representable within an unsigned char. Example output: demo.c:5:13: warning: result of '2^8' is 10; did you mean '1 << 8' (256)? [-Wxor-used-as-pow] 5 | int t2_8 = 2^8; | ^ |-- |1<< demo.c:5:12: note: you can silence this warning by using a hexadecimal constant (0x2 rather than 2) 5 | int t2_8 = 2^8; |^ |0x2 demo.c:21:15: warning: result of '10^6' is 12; did you mean '1e6'? [-Wxor-used-as-pow] 21 | int t10_6 = 10^6; | ^ | --- | 1e demo.c:21:13: note: you can silence this warning by using a hexadecimal constant (0xa rather than 10) 21 | int t10_6 = 10^6; | ^~ | 0xa Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu. OK for trunk? Thanks Dave gcc/c-family/ChangeLog: PR c/90885 * c-common.h (check_for_xor_used_as_pow): New decl. * c-lex.cc (c_lex_with_flags): Add DECIMAL_INT to flags as appropriate. * c-warn.cc (check_for_xor_used_as_pow): New. * c.opt (Wxor-used-as-pow): New. gcc/c/ChangeLog: PR c/90885 * c-parser.cc (c_parser_string_literal): Clear ret.m_decimal. (c_parser_expr_no_commas): Likewise. (c_parser_conditional_expression): Likewise. (c_parser_binary_expression): Clear m_decimal when popping the stack. (c_parser_unary_expression): Clear ret.m_decimal. (c_parser_has_attribute_expression): Likewise for result. (c_parser_predefined_identifier): Likewise for expr. (c_parser_postfix_expression): Likewise for expr. Set expr.m_decimal when handling a CPP_NUMBER that was a decimal token. * c-tree.h (c_expr::m_decimal): New bitfield. * c-typeck.cc (parser_build_binary_op): Clear result.m_decimal. (parser_build_binary_op): Call check_for_xor_used_as_pow. gcc/cp/ChangeLog: PR c/90885 * cp-tree.h (class cp_expr): Add bitfield m_decimal. Clear it in existing ctors. Add ctor that allows specifying its value. (cp_expr::decimal_p): New accessor. * parser.cc (cp_parser_expression_stack_entry::flags): New field. (cp_parser_primary_expression): Set m_decimal of cp_expr when handling numbers. (cp_parser_binary_expression): Extract flags from token when populating stack. Call check_for_xor_used_as_pow. gcc/ChangeLog: PR c/90885 * doc/invoke.texi (Warning Options): Add -Wxor-used-as-pow. gcc/testsuite/ChangeLog: PR c/90885 * c-c++-common/Wxor-used-as-pow-1.c: New test. * c-c++-common/Wxor-used-as-pow-fixits.c: New test. * g++.dg/parse/expr3.C: Convert 2 to 0x2 to suppress -Wxor-used-as-pow. * g++.dg/warn/Wparentheses-10.C: Likewise. * g++.dg/warn/Wparentheses-18.C: Likewise. * g++.dg/warn/Wparentheses-19.C: Likewise. * g++.dg/warn/Wparentheses-9.C: Likewise. * g++.dg/warn/Wxor-used-as-pow-named-op.C: New test. * gcc.dg/Wparentheses-6.c: Convert 2 to 0x2 to suppress -Wxor-used-as-pow. * gcc.dg/Wparentheses-7.c: Likewise. * gcc.dg/precedence-1.c: Likewise. libcpp/ChangeLog: PR c/90885 *
