tree-ssa-sink: Improve code sinking pass

tree-ssa-sink: Improve code sinking pass

Currently, code sinking will sink code at the use points with loop having same
nesting depth. The following patch improves code sinking by placing the sunk
code in begining of the block after the labels.

2024-05-08  Ajit Kumar Agarwal  <aagarwa1@linux.ibm.com>

gcc/ChangeLog:

	PR tree-optimization/81953
	* tree-ssa-sink.cc (statement_sink_location):Sink statements at
	the begining of the basic block after labels.

gcc/testsuite/ChangeLog:

	PR tree-optimization/81953
	* gcc.dg/tree-ssa/ssa-sink-21.c: New test.