[AIX][compiler-rt] Pick the right form of COMPILER_RT_ALIAS for AIX

[daltenty]

Summary

we use the alias attribute, similar to what is done for ELF.

[jasonliu]

LGTM.

[jasonliu]

Sorry... it does not seem to work with every compiler on AIX though. Does that mean we want to specify compiler macro along with system macro?
This is the case I tried:

int oldname = 1;
extern int newname attribute((alias("oldname")));

xlclang alias.c -c
alias.c:2:35: warning: 1540-2990 The attribute " attribute((alias("oldname")))" is not supported. The attribute is ignored.
extern int newname attribute((alias("oldname")));

[hubert.reinterpretcast]

In D81120#2085913, @jasonliu wrote:

xlclang alias.c -c
alias.c:2:35: warning: 1540-2990 The attribute " attribute((alias("oldname")))" is not supported. The attribute is ignored.
extern int newname attribute((alias("oldname")));

Do we know whether the macro is used on variables?

[daltenty]

In D81120#2086157, @hubert.reinterpretcast wrote:

In D81120#2085913, @jasonliu wrote:

xlclang alias.c -c
alias.c:2:35: warning: 1540-2990 The attribute " attribute((alias("oldname")))" is not supported. The attribute is ignored.
extern int newname attribute((alias("oldname")));

Do we know whether the macro is used on variables?

As far as I can see, COMPILER_RT_ALIAS is only used for function aliases, for which __attribute__((__alias__)) seems to be supported by XL. Given that COMPILER_RT_ABI currently expands to calling convention attributes, I think it's probably safe to conclude this macro isn't intended for use with variables.

[jasonliu]

As far as I can see, COMPILER_RT_ALIAS is only used for function aliases, for which attribute((alias)) seems to be supported by XL. Given that COMPILER_RT_ABI currently expands to calling convention attributes, I think it's probably safe to conclude this macro isn't intended for use with variables.

Thanks. In that case, this still LGTM.

compiler-rt/lib/builtins/int_lib.h

 #define NORETURN __attribute__((noreturn))
 #define UNUSED __attribute__((unused))
 #endif
 
 #define STR(a) #a
 #define XSTR(a) STR(a)
 #define SYMBOL_NAME(name) XSTR(__USER_LABEL_PREFIX__) #name
 
-#if defined(__ELF__) || defined(__MINGW32__) || defined(__wasm__)
+#if defined(__ELF__) || defined(__MINGW32__) || defined(__wasm__) ||           \
+    defined(_AIX)
 #define COMPILER_RT_ALIAS(name, aliasname) \
   COMPILER_RT_ABI __typeof(name) aliasname __attribute__((__alias__(#name)));
 #elif defined(__APPLE__)
 #if defined(VISIBILITY_HIDDEN)
 #define COMPILER_RT_ALIAS_VISIBILITY(name) \
   __asm__(".private_extern " SYMBOL_NAME(name));
 #else
 #define COMPILER_RT_ALIAS_VISIBILITY(name)