[clang] Fixes compile error that double colon operator cannot resolve macro with parentheses.

[lygstate]

Summary

Error message:

In file included from ../src/amd/addrlib/src/core/addrobject.h:21:
../src/amd/addrlib/src/core/addrcommon.h:343:13: error: expected unqualified-id
    out = ::_tzcnt_u32(mask);
            ^
/usr/lib/llvm-15/lib/clang/15.0.6/include/bmiintrin.h:74:27: note: expanded from macro '_tzcnt_u32'
#define _tzcnt_u32(a)     (__tzcnt_u32((a)))

This is because both GCC/Clang doesn't support compiling the following code:

#ifdef _MSC_VER
#include <intrin.h>
#else
#include <x86intrin.h>
#endif

int f(int a) {
    return ::(_tzcnt_u32)(a);
}

This is because the return statement expects an expression or braced init list: http://eel.is/c++draft/stmt.jump#general-1 but we really only need to care about the expression form (there's no braces in sight).
Grammatically, the leading :: will parse as a qualified-id because it matches the production for nested-name-specifier: http://eel.is/c++draft/expr.prim.id.qual#nt:qualified-id
That needs to be followed by an unqualified-id (http://eel.is/c++draft/expr.prim.id.unqual#nt:unqualified-id), but the open paren does not match any of the grammar productions, so this is a syntax error.

Closes: https://github.com/llvm/llvm-project/issues/64467

Signed-off-by: Yonggang Luo <[e-mail]>

[pengfei]

The description is not clear to me. You should describe the reason rather than phenomenon.

My understanding is double colon operator cannot resolve functions with parentheses. https://godbolt.org/z/6P47se9WW

But I didn't find enough proof in Google. It'd be more persuasive if you can find it and add to the description.

[RKSimon]

Would we be better off creating proper function definitions - we already have similar duplicates for _bextr_u64 (Intel) vs __bextr_u64 (AMD) names that do this

[lygstate]

In D157297#4571572, @pengfei wrote:

The description is not clear to me. You should describe the reason rather than phenomenon.

My understanding is double colon operator cannot resolve functions with parentheses. https://godbolt.org/z/6P47se9WW

error: expected unqualified-id

return ::_tzcnt_u32(a);
         ^

/opt/compiler-explorer/clang-16.0.0/lib/clang/16/include/bmiintrin.h:74:27: note: expanded from macro '_tzcnt_u32'
#define _tzcnt_u32(a) (__tzcnt_u32((a)))

Looks like double colon operator cannot resolve macros with parentheses, is that a compiler bug or we should handled it in code?

But I didn't find enough proof in Google. It'd be more persuasive if you can find it and add to the description.

[pengfei]

In D157297#4583802, @lygstate wrote:

In D157297#4571572, @pengfei wrote:

The description is not clear to me. You should describe the reason rather than phenomenon.

My understanding is double colon operator cannot resolve functions with parentheses. https://godbolt.org/z/6P47se9WW

error: expected unqualified-id

return ::_tzcnt_u32(a);
         ^

/opt/compiler-explorer/clang-16.0.0/lib/clang/16/include/bmiintrin.h:74:27: note: expanded from macro '_tzcnt_u32'
#define _tzcnt_u32(a) (__tzcnt_u32((a)))

Looks like double colon operator cannot resolve macros with parentheses, is that a compiler bug or we should handled it in code?

But I didn't find enough proof in Google. It'd be more persuasive if you can find it and add to the description.

GCC doesn't resolve it either. https://godbolt.org/z/Prb4s5d6o. So it should not be a bug.

[lygstate]

creating proper function definitions instead of macro define

[pengfei]

I'd prefer macro to duplicated definitions. We have such precedents, e.g., https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/xmmintrin.h#L2994
Besides, you should update the summary as well.

[lygstate]

In D157297#4590580, @pengfei wrote:

I'd prefer macro to duplicated definitions. We have such precedents, e.g., https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/xmmintrin.h#L2994

Do you means revert to the first version?

Besides, you should update the summary as well.

I don't know what kind of summary you want, You can give me that so I can update it

[pengfei]

In D157297#4590692, @lygstate wrote:

In D157297#4590580, @pengfei wrote:

I'd prefer macro to duplicated definitions. We have such precedents, e.g., https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/xmmintrin.h#L2994

Do you means revert to the first version?

Yes.

Besides, you should update the summary as well.

I don't know what kind of summary you want, I can give me that so I can update it

A reliable source about double colon operator cannot resolve function with parentheses in C++ is the best I expect, however I haven't find one so far.
Maybe a short description about the phenomenon on GCC/Clang is better than just giving error message. I don't have strong request for this.

[lygstate]

Revert to version 1

[pengfei]

LGTM.

[pengfei]

BTW, maybe @aaron.ballman knows why we don't support such syntax in C++.

[aaron.ballman]

In D157297#4590886, @pengfei wrote:

BTW, maybe @aaron.ballman knows why we don't support such syntax in C++.

The return statement expects an expression or braced init list: http://eel.is/c++draft/stmt.jump#general-1 but we really only need to care about the expression form (there's no braces in sight).
Grammatically, the leading :: will parse as a qualified-id because it matches the production for nested-name-specifier: http://eel.is/c++draft/expr.prim.id.qual#nt:qualified-id
That needs to be followed by an unqualified-id (http://eel.is/c++draft/expr.prim.id.unqual#nt:unqualified-id), but the open paren does not match any of the grammar productions, so this is a syntax error.

[pengfei]

In D157297#4592851, @aaron.ballman wrote:

In D157297#4590886, @pengfei wrote:

BTW, maybe @aaron.ballman knows why we don't support such syntax in C++.

The return statement expects an expression or braced init list: http://eel.is/c++draft/stmt.jump#general-1 but we really only need to care about the expression form (there's no braces in sight).
Grammatically, the leading :: will parse as a qualified-id because it matches the production for nested-name-specifier: http://eel.is/c++draft/expr.prim.id.qual#nt:qualified-id
That needs to be followed by an unqualified-id (http://eel.is/c++draft/expr.prim.id.unqual#nt:unqualified-id), but the open paren does not match any of the grammar productions, so this is a syntax error.

Thanks @aaron.ballman for the detailed explanation! I have learnt it. @lygstate maybe include Aaron's explanation in commit message?

[lygstate]

Thanks @aaron.ballman for the detailed explanation! I have learnt it. @lygstate maybe include Aaron's explanation in commit message?

The commit message is updated, is that ready for merge?

clang/lib/Headers/bmiintrin.h

    to use it as a potentially faster version of BSF. */
 #define __RELAXED_FN_ATTRS __attribute__((__always_inline__, __nodebug__))
 
-#define _tzcnt_u16(a)     (__tzcnt_u16((a)))
+#define _tzcnt_u16 __tzcnt_u16
 
 /// Counts the number of trailing zero bits in the operand.
 ///

   return (int)__builtin_ia32_tzcnt_u32(__X);
 }
 
-#define _tzcnt_u32(a)     (__tzcnt_u32((a)))
+#define _tzcnt_u32 __tzcnt_u32
 
 #ifdef __x86_64__
 

   return (long long)__builtin_ia32_tzcnt_u64(__X);
 }
 
-#define _tzcnt_u64(a)     (__tzcnt_u64((a)))
+#define _tzcnt_u64 __tzcnt_u64
 
 #endif /* __x86_64__ */
 

 /* Define the default attributes for the functions in this file. */
 #define __DEFAULT_FN_ATTRS __attribute__((__always_inline__, __nodebug__, __target__("bmi")))
 
-#define _andn_u32(a, b)   (__andn_u32((a), (b)))
+#define _andn_u32 __andn_u32
 
 /* _bextr_u32 != __bextr_u32 */
-#define _blsi_u32(a)      (__blsi_u32((a)))
+#define _blsi_u32 __blsi_u32
 
-#define _blsmsk_u32(a)    (__blsmsk_u32((a)))
+#define _blsmsk_u32 __blsmsk_u32
 
-#define _blsr_u32(a)      (__blsr_u32((a)))
+#define _blsr_u32 __blsr_u32
 
 /// Performs a bitwise AND of the second operand with the one's
 ///    complement of the first operand.

 
 #ifdef __x86_64__
 
-#define _andn_u64(a, b)   (__andn_u64((a), (b)))
+#define _andn_u64 __andn_u64
 
 /* _bextr_u64 != __bextr_u64 */
-#define _blsi_u64(a)      (__blsi_u64((a)))
+#define _blsi_u64 __blsi_u64
 
-#define _blsmsk_u64(a)    (__blsmsk_u64((a)))
+#define _blsmsk_u64 __blsmsk_u64
 
-#define _blsr_u64(a)      (__blsr_u64((a)))
+#define _blsr_u64 __blsr_u64
 
 /// Performs a bitwise AND of the second operand with the one's
 ///    complement of the first operand.