PR rtl-optimization/88796
	* emit-rtl.h (struct rtl_data): Add stack_protect_guard_decl field.
	* cfgexpand.c (stack_protect_prologue): Initialize
	crtl->stack_protect_guard_decl.
	* function.c (stack_protect_epilogue): Use it instead of calling
	targetm.stack_protect_guard again.
	* dse.c (check_mem_read_rtx): Ignore MEM_VOLATILE_P reads from
	MEMs with MEM_EXPR equal to crtl->stack_protect_guard or
	crtl->stack_protect_guard_decl.
	* config/i386/i386.c (ix86_stack_protect_guard): Set TREE_THIS_VOLATILE
	on the returned MEM_EXPR.

	* gcc.target/i386/pr88796.c: New test.

From-SVN: r267916