| Message ID | cc9556c3-e893-d6b7-d8c5-ff571a866604@suse.cz |
|---|---|
| State | New |
| Headers | show |
| Series | Do not remove ifunc_resolver in LTO. | expand |
On Mon, 2020-04-20 at 11:34 +0200, Martin Liška wrote: > Hi. > > The patch prevents a ifunc alias from removal in remove unreachable nodes. > Note that ifunc alias lives in a COMDAT section and so that > cgraph_node::can_remove_if_no_direct_calls_and_refs_p returned true for it. > > Patch can bootstrap on x86_64-linux-gnu and survives regression tests. > I was unable to create a lto test-case where a linked binary could be > scanned for assembly. > > Ready to be installed? > Thanks, > Martin > > gcc/ChangeLog: > > 2020-04-20 Martin Liska <mliska@suse.cz> > > PR lto/94659 > * cgraph.h (cgraph_node::can_remove_if_no_direct_calls_and_refs_p): > Do not remove ifunc_resolvers in remove unreachable nodes in LTO. OK jeff
> On Mon, 2020-04-20 at 11:34 +0200, Martin Liška wrote: > > Hi. > > > > The patch prevents a ifunc alias from removal in remove unreachable nodes. > > Note that ifunc alias lives in a COMDAT section and so that > > cgraph_node::can_remove_if_no_direct_calls_and_refs_p returned true for it. > > > > Patch can bootstrap on x86_64-linux-gnu and survives regression tests. > > I was unable to create a lto test-case where a linked binary could be > > scanned for assembly. > > > > Ready to be installed? > > Thanks, > > Martin > > > > gcc/ChangeLog: > > > > 2020-04-20 Martin Liska <mliska@suse.cz> > > > > PR lto/94659 > > * cgraph.h (cgraph_node::can_remove_if_no_direct_calls_and_refs_p): > > Do not remove ifunc_resolvers in remove unreachable nodes in LTO. > OK Is it intended to keep the comdat group alive even when the function is not used by the current translation unit? Honza > jeff >
On 4/22/20 8:11 PM, Jan Hubicka wrote: >> On Mon, 2020-04-20 at 11:34 +0200, Martin Liška wrote: >>> Hi. >>> >>> The patch prevents a ifunc alias from removal in remove unreachable nodes. >>> Note that ifunc alias lives in a COMDAT section and so that >>> cgraph_node::can_remove_if_no_direct_calls_and_refs_p returned true for it. >>> >>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests. >>> I was unable to create a lto test-case where a linked binary could be >>> scanned for assembly. >>> >>> Ready to be installed? >>> Thanks, >>> Martin >>> >>> gcc/ChangeLog: >>> >>> 2020-04-20 Martin Liska <mliska@suse.cz> >>> >>> PR lto/94659 >>> * cgraph.h (cgraph_node::can_remove_if_no_direct_calls_and_refs_p): >>> Do not remove ifunc_resolvers in remove unreachable nodes in LTO. >> OK > Is it intended to keep the comdat group alive even when the function is > not used by the current translation unit? Yes, if you take a look at the mentioned PR, the function is exported and used by a different TU. Or do you have a particular test-case which you're talking about? Martin > > Honza >> jeff >>
> On 4/22/20 8:11 PM, Jan Hubicka wrote: > > > On Mon, 2020-04-20 at 11:34 +0200, Martin Liška wrote: > > > > Hi. > > > > > > > > The patch prevents a ifunc alias from removal in remove unreachable nodes. > > > > Note that ifunc alias lives in a COMDAT section and so that > > > > cgraph_node::can_remove_if_no_direct_calls_and_refs_p returned true for it. > > > > > > > > Patch can bootstrap on x86_64-linux-gnu and survives regression tests. > > > > I was unable to create a lto test-case where a linked binary could be > > > > scanned for assembly. > > > > > > > > Ready to be installed? > > > > Thanks, > > > > Martin > > > > > > > > gcc/ChangeLog: > > > > > > > > 2020-04-20 Martin Liska <mliska@suse.cz> > > > > > > > > PR lto/94659 > > > > * cgraph.h (cgraph_node::can_remove_if_no_direct_calls_and_refs_p): > > > > Do not remove ifunc_resolvers in remove unreachable nodes in LTO. > > > OK > > Is it intended to keep the comdat group alive even when the function is > > not used by the current translation unit? > > Yes, if you take a look at the mentioned PR, the function is exported and used > by a different TU. > > Or do you have a particular test-case which you're talking about? Well, first I think you want to use force_output flag when you create the alias instead of modifying can_remove_if_no_direct_calls_and_refs_p. I wonder what happens when your function is static and we optimize away all uses of it - then I think GCC should optimize it away. Similarly if the function is comdat: __attribute__((target_clones("default,avx"))) inline int f1() { return 2; } int main() { return f1(); } We should avoid outputting it to every compilation unit that includes the header. I do not recall, why that function is comdat at first place? Honza
diff --git a/gcc/cgraph.h b/gcc/cgraph.h index 43de3b4a8ac..5ddeb65269b 100644 --- a/gcc/cgraph.h +++ b/gcc/cgraph.h @@ -3162,7 +3162,7 @@ cgraph_node::can_remove_if_no_direct_calls_and_refs_p (void) return false; /* Only COMDAT functions can be removed if externally visible. */ if (externally_visible - && (!DECL_COMDAT (decl) + && ((!DECL_COMDAT (decl) || ifunc_resolver) || forced_by_abi || used_from_object_file_p ())) return false;