re PR tree-optimization/79697 (unused realloc(0, n) not eliminated)

re PR tree-optimization/79697 (unused realloc(0, n) not eliminated)

2017-04-29  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>

	PR tree-optimization/79697
	* tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Check if callee
	is BUILT_IN_STRDUP, BUILT_IN_STRNDUP, BUILT_IN_REALLOC.
	(propagate_necessity): Check if def_callee is BUILT_IN_STRDUP or
	BUILT_IN_STRNDUP.
	* gimple-fold.c (gimple_fold_builtin_realloc): New function.
	(gimple_fold_builtin): Call gimple_fold_builtin_realloc.

testsuite/
	* gcc.dg/tree-ssa/pr79697.c: New test.

From-SVN: r247407