[Patch] catch builtin_bswap16 construct

[Eric Botcazou]

> A while ago I've tried doing that for SH (implementing bswap16 with RTL
> combine).  It was like an explosion of patterns, because combine would
> try out a lot of things depending on the surrounding code around the
> actual bswap16.  In the end I decided to drop that stuff for the most
> part.

OK, thanks for your feedback.  Note that you won't get the benefit of the 
optimization for SH if you don't define a bswaphi2 pattern.

> BTW, the built-in documentation says:
> 
> Built-in Function: int16_t __builtin_bswap16 (int16_t x)
> Built-in Function: int32_t __builtin_bswap32 (int32_t x)
> 
> However, it seems the result is always unsigned for those.

Yes, builtins.def contains:

DEF_GCC_BUILTIN        (BUILT_IN_BSWAP16, "bswap16", BT_FN_UINT16_UINT16, 
ATTR_CONST_NOTHROW_LEAF_LIST)
DEF_GCC_BUILTIN        (BUILT_IN_BSWAP32, "bswap32", BT_FN_UINT32_UINT32, 
ATTR_CONST_NOTHROW_LEAF_LIST)
DEF_GCC_BUILTIN        (BUILT_IN_BSWAP64, "bswap64", BT_FN_UINT64_UINT64, 
ATTR_CONST_NOTHROW_LEAF_LIST)

The documentation indeed needs to be fixed.

-- 
Eric Botcazou