[clang][SVE] Use __inline__ instead of inline in arm_sve.h

[joechrisellis]

Summary

The inline keyword is not defined in the C89 standard, so source files
that include arm_sve.h will fail compilation if -std=c89 is specified.
For consistency with arm_neon.h, we should use inline instead.

[joechrisellis]

Speaking to @DavidTruby about this, it appears that this fix is insufficient -- inline has important semantic meaning in C++ that means that we can't simply omit the keyword here.

The inline keyword bypasses the one-definition rule. If we have a function defined in a header that isn't marked inline, and you include that header in two different source files, then your program is ill formed because it contains 2 definitions of that function. So we have to keep it for C++.

[paulwalker-arm]

In D96852#2568383, @joechrisellis wrote:

Speaking to @DavidTruby about this, it appears that this fix is insufficient -- inline has important semantic meaning in C++ that means that we can't simply omit the keyword here.

The inline keyword bypasses the one-definition rule. If we have a function defined in a header that isn't marked inline, and you include that header in two different source files, then your program is ill formed because it contains 2 definitions of that function. So we have to keep it for C++.

That makes sense and suggests we're missing some additional C++ testing?

[tschuett]

See

__STDC_VERSION__

in https://gcc.gnu.org/onlinedocs/cpp/Standard-Predefined-Macros.html.

[joechrisellis]

That makes sense and suggests we're missing some additional C++ testing?

Agreed -- this passes all tests at the moment, so we can do better test-wise. The error to do with the one definition rule would crop up at link time, though, so we'd need at least two compilation units to validate this.

[paulwalker-arm]

One observation is that for arm_neon.h __inline__ is used. So perhaps we can just do likewise and we'll also be consistent across the two ACLE headers?

[joechrisellis]

Use inline instead of inline.

clang/utils/TableGen/SveEmitter.cpp

void SVEEmitter::createHeader(raw_ostream &OS) {
   OS << "  SV_PSTL1STRM = 9,\n";
   OS << "  SV_PSTL2KEEP = 10,\n";
   OS << "  SV_PSTL2STRM = 11,\n";
   OS << "  SV_PSTL3KEEP = 12,\n";
   OS << "  SV_PSTL3STRM = 13\n";
   OS << "};\n\n";
 
   OS << "/* Function attributes */\n";
-  OS << "#define __aio static inline __attribute__((__always_inline__, "
+  OS << "#define __aio static __inline__ __attribute__((__always_inline__, "
         "__nodebug__, __overloadable__))\n\n";
 
   // Add reinterpret functions.
   for (auto ShortForm : { false, true } )
     for (const ReinterpretTypeInfo &From : Reinterprets)
       for (const ReinterpretTypeInfo &To : Reinterprets) {
         const bool IsBFloat = StringRef(From.Suffix).equals("bf16") ||
                               StringRef(To.Suffix).equals("bf16");