lra: emit caller-save register spills before call insn [PR116028]

LRA emits insns to save caller-save registers in the
inheritance/splitting pass. In this pass, LRA builds EBBs (Extended
Basic Block) and traverses the insns in the EBBs in reverse order from
the last insn to the first insn. When LRA sees a write to a pseudo (that
has been assigned a caller-save register), and there is a read following
the write, with an intervening call insn between the write and read,
then LRA generates a spill immediately after the write and a restore
immediately before the read. The spill is needed because the call insn
will clobber the caller-save register.

If there is a write insn and a call insn in two separate BBs but
belonging to the same EBB, the spill insn gets generated in the BB
containing the write insn. If the write insn is in the entry BB, then
the spill insn that is generated in the entry BB prevents shrink wrap
from happening. This is because the spill insn references the stack
pointer and hence the prolog gets generated in the entry BB itself.

This patch ensures the the spill insn is generated before the call insn
instead of after the write. This also ensures that the spill occurs
only in the path containing the call.

2024-08-01  Surya Kumari Jangala  <jskumari@linux.ibm.com>

gcc:
	PR rtl-optimization/116028
	* lra-constraints.cc (split_reg): Spill register before call
	insn.
	(latest_call_insn): New variable.
	(inherit_in_ebb): Track the latest call insn.

gcc/testsuite:
	PR rtl-optimization/116028
	* gcc.dg/ira-shrinkwrap-prep-1.c: Remove xfail for powerpc.
	* gcc.dg/pr10474.c: Remove xfail for powerpc.