Sometimes a local variable is used as a return value in a case where the return value is always 0. The result is more apparent if this variable is just replaced by 0. This is done by the following semantic patch, although some cleanups may be needed. (http://coccinelle.lip6.fr/)
// <smpl> @r exists@ local idexpression ret; identifier reti; expression e; position p; @@
ret@reti = 0; ... when != (ret = e|ret &= e|ret |= e|ret += e|ret -= e|ret *= e|ret ^= e) when != (++ret|--ret|ret++|ret--) when != &ret return ret;@p
@bad1 exists@ expression e != 0; local idexpression r.ret; position r.p; @@
(ret = e|ret &= e|ret |= e|ret += e|ret -= e|ret *= e|ret ^= e|++ret|--ret|ret++|ret--|&ret) ... return ret;@p
@bad2 exists@ identifier r.reti; position r.p; identifier f; type T; @@
f(...,T reti,...) { ... return reti;@p }
@change depends on !bad1 && !bad2@ position r.p; local idexpression r.ret; identifier f; @@
f(...) { <+... return -ret +0 ;@p ...+> }
@rewrite@ local idexpression r.ret; expression e; position p; identifier change.f; @@
f(...) { <+... (ret@p = e|&ret@p) ...+> }
@depends on change@ local idexpression r.ret; position p != rewrite.p; identifier change.f; @@
f(...) { <+... ( break; | ret = 0; ... when exists ret@p ... when any | - ret = 0; ) ...+> }
@depends on change@ identifier r.reti; type T; constant C; identifier change.f; @@
f(...) { ... when any -T reti = C; ... when != reti when strict }
@depends on change@ identifier r.reti; type T; identifier change.f; @@
f(...) { ... when any -T reti; ... when != reti when strict } // </smpl>
The first four rules detect cases where only 0 reaches a return. The remaining rules clean up any variable initializations or declarations that are made unnecessary by this change.