On 8 June 2017 14:52:49 CEST, Jan Hubicka <[email protected]> wrote:
>Hi,
>this patch adds static code to detect basic block with 0 execution
>count.
>Those are basic block either reached only by EH or those which leads to
>call of
>function decorated with cold attribute.
>
>Function decorated by noreturn is not sufficient, because exit(0) is a
>call that
>is executed in most of program executions.
But aren't paths to exit except in main cold resp unlikely, at least exit (!0)?
>
>Note that internally we have cold and unlikely functions where the
>first is
>optimized for size but the second is known to be unlikely executed by
>the
>program and is offloaded to special unlikely section.
>Perhaps we want to expose this to user and also distinguish between
>cold and
>unlikely function attributes. I guess this however can be done
>incrementally.
>
>As a followup I will decoreate trap/abort and friends with cold
>attributes.
>
>Bootstrapped/regtested x86_64-linux, will commit it shortly.
>
>+/* Return true if STMT is known to be unlikely executed. */
>+
>+static bool
>+unlikely_executed_stmt_p (gimple *stmt)
>+{
>+ if (!is_gimple_call (stmt))
>+ return false;
>+ /* NORETURN attribute enough is not strong enough: exit() may be
s/attribute enough/attribute alone/
>quite
>+ likely executed once during program run. */
>+ if (gimple_call_fntype (stmt)
>+ && lookup_attribute ("cold",
>+ TYPE_ATTRIBUTES (gimple_call_fntype (stmt)))
>+ && !lookup_attribute ("cold", DECL_ATTRIBUTES
>(current_function_decl)))
>+ return true;
>+ tree decl = gimple_call_fndecl (stmt);
>+ if (!decl)
>+ return false;
Can decl ever be NULL here?
>+ if (lookup_attribute ("cold", DECL_ATTRIBUTES (decl))
>+ && !lookup_attribute ("cold", DECL_ATTRIBUTES
>(current_function_decl)))
>+ return true;
>+
>+ cgraph_node *n = cgraph_node::get (decl);
>+ if (!n)
>+ return false;
>+ enum availability avail;
Didn't style want us to omit enum here since its C++ now?
>+ n = n->ultimate_alias_target (&avail);
>+ if (avail < AVAIL_AVAILABLE)
>+ return NULL;
false
thanks,
>+ if (!n->analyzed
>+ || n->decl == current_function_decl)
>+ return false;
>+ return n->frequency == NODE_FREQUENCY_UNLIKELY_EXECUTED;
>+}
