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, 54 insertions, 0 deletions

diff --git a/libgomp/testsuite/libgomp.c/declare-variant-1.c b/libgomp/testsuite/libgomp.c/declare-variant-1.c
new file mode 100644
index 0000000..d16608f
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c/declare-variant-1.c
@@ -0,0 +1,54 @@
+/* { dg-do link { target vect_simd_clones } } */
+/* { dg-require-effective-target lto } */
+/* { dg-require-effective-target fpic } */
+/* { dg-require-effective-target shared } */
+/* { dg-additional-options "-fdump-tree-gimple -fdump-tree-optimized -O2 -fPIC -shared -flto -flto-partition=one" } */
+/* { dg-additional-options "-mno-sse3" { target { i?86-*-* x86_64-*-* } } } */
+
+int
+f01 (int a)
+{
+  asm volatile ("" : "+g" (a) : "g" (1) : "memory");
+  return a;
+}
+
+int
+f02 (int a)
+{
+  asm volatile ("" : "+g" (a) : "g" (2) : "memory");
+  return a;
+}
+
+int
+f03 (int a)
+{
+  asm volatile ("" : "+g" (a) : "g" (3) : "memory");
+  return a;
+}
+
+#pragma omp declare variant (f01) match (device={isa("avx512f")}) /* 4 or 8 */
+#pragma omp declare variant (f02) match (implementation={vendor(score(3):gnu)},device={kind(cpu)}) /* (1 or 2) + 3 */
+#pragma omp declare variant (f03) match (implementation={vendor(score(5):gnu)},device={kind(host)}) /* (1 or 2) + 5 */
+int
+f04 (int a)
+{
+  asm volatile ("" : "+g" (a) : "g" (4) : "memory");
+  return a;
+}
+
+#pragma omp declare simd
+int
+test1 (int x)
+{
+  /* At gimplification time, we can't decide yet which function to call.  */
+  /* { dg-final { scan-tree-dump-times "f04 \\\(x" 2 "gimple" } } */
+  /* After simd clones are created, the original non-clone test1 shall
+     call f03 (score 6), the sse2/avx/avx2 clones too, but avx512f clones
+     shall call f01 with score 8.  */
+  /* { dg-final { scan-ltrans-tree-dump-not "f04 \\\(x" "optimized" } } */
+  /* { dg-final { scan-ltrans-tree-dump-times "f03 \\\(x" 14 "optimized" } } */
+  /* { dg-final { scan-ltrans-tree-dump-times "f01 \\\(x" 4 "optimized" } } */
+  int a = f04 (x);
+  int b = f04 (x);
+  return a + b;
+}