| Message ID | 2199082.ElGaqSPkdT@fomalhaut |
|---|---|
| State | New |
| Headers | show |
| Series | Tame fix for PR ipa/99122 | expand |
On Wed, Jun 2, 2021 at 2:05 PM Eric Botcazou <botcazou@adacore.com> wrote: > > Hi, > > as explained in the audit trail, the return part has a major performance > impact in Ada where variable-sized types are first-class citizens, but it > turns out that it is not exercized in the testsuite yet. > > Tested on x86-64/Linux, OK for mainline and 11 branch? Not sure whether we know VLA results are always returned by reference? In particular does this mean we'll never see a WITH_SIZE_EXPR on the LHS of a call? You might have noticed I've done WITH_SIZE_EXPR "enhancements" recently on trunk. As for the patch we indeed didn't have a testcase covering the return case so it should be safe to revert the return part. I still wonder about the WITH_SIZE_EXPR here ;) Richard. > > 2021-06-02 Eric Botcazou <ebotcazou@adacore.com> > > PR ipa/99122 > * tree-inline.c (inline_forbidden_p): Remove test on return type. > > > 2021-06-02 Eric Botcazou <ebotcazou@adacore.com> > > * gnat.dg/inline22.adb: New test. > > -- > Eric Botcazou
> Not sure whether we know VLA results are always returned by > reference? In particular does this mean we'll never see a > WITH_SIZE_EXPR on the LHS of a call? You might have noticed > I've done WITH_SIZE_EXPR "enhancements" recently on trunk. VLAs are always aggregate_value_p so the caller passes the address of the return slot, but they are not always DECL_BY_REFERENCE, at least in Ada. In Ada we use DECL_BY_REFERENCE only for self-referential types, i.e. types whose size is not the same for all the objects, because we need to control the amount of returned bytes on a case-by-case basis; when the size is uniform, this complication is unnecessary. > As for the patch we indeed didn't have a testcase covering the > return case so it should be safe to revert the return part. OK, thanks, patch installed.
diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c index d38e8617e3d..cc7168614c0 100644 --- a/gcc/tree-inline.c +++ b/gcc/tree-inline.c @@ -4004,17 +4004,11 @@ inline_forbidden_p (tree fndecl) wi.info = (void *) fndecl; wi.pset = &visited_nodes; - /* We cannot inline a function with a VLA typed argument or result since - we have no implementation materializing a variable of such type in - the caller. */ - if (COMPLETE_TYPE_P (TREE_TYPE (TREE_TYPE (fndecl))) - && !poly_int_tree_p (TYPE_SIZE (TREE_TYPE (TREE_TYPE (fndecl))))) - { - inline_forbidden_reason - = G_("function %q+F can never be inlined because " - "it has a VLA return argument"); - return true; - } + /* We cannot inline a function with a variable-sized parameter because we + cannot materialize a temporary of such a type in the caller if need be. + + Note that the return case is not symmetrical because we can guarantee + that a temporary is not needed by means of CALL_EXPR_RETURN_SLOT_OPT. */ for (tree parm = DECL_ARGUMENTS (fndecl); parm; parm = DECL_CHAIN (parm)) if (!poly_int_tree_p (DECL_SIZE (parm))) {