re PR rtl-optimization/88253 (Inlining of function incorrectly deletes volatile register access when using XOR in avr-gcc)

Fix PR 88253

gcc/ChangeLog:

	PR rtl-optimization/88253
	* combine.c (combine_simplify_rtx): Test for side-effects before
	substituting by zero.

gcc/testsuite/ChangeLog:

	PR rtl-optimization/88253
	* gcc.target/avr/pr88253.c: New test.

From-SVN: r267198