lto: LTO cgraph support for late declare variant resolution [PR96680]

> I've tried to add the saving/restoring next to ipa refs saving/restoring, as
> the declare variant alt stuff is kind of extension of those, unfortunately
> following doesn't compile, because I need to also write or read a tree there
> (ctx is a portion of DECL_ATTRIBUTES of the base function), but the ipa refs
> write/read back functions don't have arguments that can be used for that.

This patch adds the streaming out and in of those omp_declare_variant_alt
hash table on the side data for the declare_variant_alt cgraph_nodes and
treats for LTO purposes the declare_variant_alt nodes (which have no body)
as if they contained a body that calls all the possible variants.
After IPA all the calls to these magic declare_variant_alt calls are
replaced with call to one of the variant depending on which one has the
highest score in the context.

2020-10-28  Jakub Jelinek  <jakub@redhat.com>

	PR lto/96680
gcc/
	* lto-streamer.h (omp_lto_output_declare_variant_alt,
	omp_lto_input_declare_variant_alt): Declare variant.
	* symtab.c (symtab_node::get_partitioning_class): Return
	SYMBOL_DUPLICATE for declare_variant_alt nodes.
	* passes.c (ipa_write_summaries): Add declare_variant_alt to
	partition.
	* lto-cgraph.c (output_refs): Call omp_lto_output_declare_variant_alt
	on declare_variant_alt nodes.
	(input_refs): Call omp_lto_input_declare_variant_alt on
	declare_variant_alt nodes.
	* lto-streamer-out.c (output_function): Don't call
	collect_block_tree_leafs if DECL_INITIAL is error_mark_node.
	(lto_output): Call output_function even for declare_variant_alt
	nodes.
	* omp-general.c (omp_lto_output_declare_variant_alt,
	omp_lto_input_declare_variant_alt): New functions.
gcc/lto/
	* lto-common.c (lto_fixup_prevailing_decls): Don't use
	LTO_NO_PREVAIL on TREE_LIST's TREE_PURPOSE.
	* lto-partition.c (lto_balanced_map): Treat declare_variant_alt
	nodes like definitions.
libgomp/
	* testsuite/libgomp.c/declare-variant-1.c: New test.

1 files changed, 6 insertions, 0 deletions

diff --git a/gcc/lto-cgraph.c b/gcc/lto-cgraph.c
index 19d4ca5..91900a1 100644
--- a/gcc/lto-cgraph.c
+++ b/gcc/lto-cgraph.c
@@ -767,6 +767,9 @@ output_refs (lto_symtab_encoder_t encoder)
 	  for (int i = 0; node->iterate_reference (i, ref); i++)
 	    lto_output_ref (ob, ref, encoder);
 	}
+      if (cgraph_node *cnode = dyn_cast <cgraph_node *> (node))
+	if (cnode->declare_variant_alt)
+	  omp_lto_output_declare_variant_alt (ob, cnode, encoder);
     }
 
   streamer_write_uhwi_stream (ob->main_stream, 0);
@@ -1608,6 +1611,9 @@ input_refs (class lto_input_block *ib,
 	  input_ref (ib, node, nodes);
 	  count--;
 	}
+      if (cgraph_node *cnode = dyn_cast <cgraph_node *> (node))
+	if (cnode->declare_variant_alt)
+	  omp_lto_input_declare_variant_alt (ib, cnode, nodes);
     }
 }