forwprop: Fix copy prop aggregates into return statements slightly [PR124099]

forwprop: Fix copy prop aggregates into return statements slightly [PR124099]

So a few more restrictions are needed here.
First we don't need to change if the return statement is already
a RESULT_DECL nor deference of the RESULT_DECL.
Second proping a global variable into the return is ok for the most
part except enumtls does not know how to expand that correctly and things
go down hill. So restrict to non global vars now.

Bootstrapped and tested on x86_64-linux-gnu.
Also tested the testcase with TLS turned off so enumtls ran.

	PR tree-optimization/124099

gcc/ChangeLog:

	* tree-ssa-forwprop.cc (optimize_agr_copyprop_return): Don't do anything
	if the return is already result decl or a deference of result decl.
	Also reject non local var decls.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/tls-return-1.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>