re PR rtl-optimization/78812 (Wrong code generation due to hoisting memory load across function call)

	PR tree-optimizatin/78812
	* rtl.h (contains_mem_rtx_p): Prototype.
	* ifcvt.c (containts_mem_rtx_p): Move from here to...
	* rtlanal.c (contains_mem_rtx_p): Here and remvoe static linkage.
	* gcse.c (prune_expressions): Use contains_mem_rtx_p to discover
	and prune MEMs that are not at the toplevel of a SET_SRC rtx.  Look
	through ZERO_EXTEND and SIGN_EXTEND when trying to avoid pruning
	MEMs.

	PR tree-optimization/78812
	* g++.dg/torture/pr78812.C: New test.

From-SVN: r244093