rs6000: Handle pcrel sibcalls to longcall functions [PR104894]

rs6000: Handle pcrel sibcalls to longcall functions [PR104894]

Before PCREL in POWER10, we were not allowed to perform sibcalls to longcall
functions since callee's return would skip the TOC restore in the caller.
However, with PCREL we can now safely perform a sibling call to longcall
functions.  The problem with the current code is that pcrel sibcall
branches to a PLT stub label even though -fno-plt was used.  The solution
here is to check for a pcrel longcall and emit an inline plt stub in
that case.

2022-04-11  Peter Bergner  <bergner@linux.ibm.com>

gcc/
	PR target/104894
	* config/rs6000/rs6000.cc (rs6000_sibcall_aix): Handle pcrel sibcalls
	to longcall functions.

gcc/testsuite/
	PR target/104894
	* gcc.target/powerpc/pr104894.c: New test.
	* gcc.target/powerpc/pr104894-2.c: New test.