[v2,1/1] C: Support Function multiversionsing in the C front end

diff --git a/gcc/c-family/c-gimplify.cc b/gcc/c-family/c-gimplify.cc
index 09ea1b79159..d288303d118 100644
--- a/gcc/c-family/c-gimplify.cc
+++ b/gcc/c-family/c-gimplify.cc
@@ -43,6 +43,7 @@  along with GCC; see the file COPYING3.  If not see
 #include "context.h"
 #include "tree-pass.h"
 #include "internal-fn.h"
+#include "calls.h"
 
 /*  The gimplification pass converts the language-dependent trees
     (ld-trees) emitted by the parser into language-independent trees
@@ -904,6 +905,16 @@  c_gimplify_expr (tree *expr_p, gimple_seq *pre_p ATTRIBUTE_UNUSED,
     case CALL_EXPR:
       {
 	tree fndecl = get_callee_fndecl (*expr_p);
+
+	/* Change any calls to a multiversioned function to instead
+	 * be a call to the dispatched symbol.  */
+	if (fndecl && DECL_FUNCTION_VERSIONED (fndecl))
+	  if (tree dis = get_c_function_version_dispatcher (fndecl))
+	    {
+	      dis = build_fold_addr_expr_loc (EXPR_LOCATION (dis), dis);
+	      CALL_EXPR_FN (*expr_p) = dis;
+	    }
+
 	if (fndecl
 	    && fndecl_built_in_p (fndecl, BUILT_IN_CLZG, BUILT_IN_CTZG)
 	    && call_expr_nargs (*expr_p) == 2
diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 1827bbf0646..686283cced6 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -62,6 +62,7 @@  along with GCC; see the file COPYING3.  If not see
 #include "omp-general.h"
 #include "omp-offload.h"  /* For offload_vars.  */
 #include "c-parser.h"
+#include "tree.h"
 
 #include "tree-pretty-print.h"
 
@@ -2098,6 +2099,22 @@  previous_tag (tree type)
   return NULL_TREE;
 }
 
+/* Subroutine to mark functions as versioned when using the attribute
+   'target_version'.  */
+
+static void
+maybe_mark_function_versioned (tree decl)
+{
+  if (!DECL_FUNCTION_VERSIONED (decl))
+    {
+      DECL_FUNCTION_VERSIONED (decl) = true;
+
+      tree mangled_name
+	= targetm.mangle_decl_assembler_name (decl, DECL_NAME (decl));
+      SET_DECL_ASSEMBLER_NAME (decl, mangled_name);
+    }
+}
+
 /* Subroutine of duplicate_decls.  Compare NEWDECL to OLDDECL.
    Returns true if the caller should proceed to merge the two, false
    if OLDDECL should simply be discarded.  As a side effect, issues
@@ -2418,7 +2435,39 @@  diagnose_mismatched_decls (tree newdecl, tree olddecl,
 	    }
 	}
 
-      if (DECL_INITIAL (newdecl))
+      if ((DECL_INITIAL (newdecl) || DECL_EXTERNAL (newdecl))
+	  && (DECL_INITIAL (olddecl) || DECL_EXTERNAL (olddecl))
+	  && targetm.target_option.function_versions (newdecl, olddecl))
+	{
+	  /* Check if we are dealing with Function Multi Versioning using
+	   the 'target_version' attribute.  */
+	  tree olddecl_args = TYPE_ARG_TYPES (TREE_TYPE (olddecl));
+	  tree newdecl_args = TYPE_ARG_TYPES (TREE_TYPE (newdecl));
+	  /* Function Multi Versioned functions need to have the same
+	     prototype and the target must support these too, otherwise
+	     error.
+	     TODO: should we be checking any other properties?  */
+	  if (!comptypes (TREE_TYPE (olddecl), TREE_TYPE (newdecl))
+	      || !comptypes (olddecl_args, newdecl_args))
+	    {
+	      auto_diagnostic_group d;
+	      error ("redefinition of %q+D", newdecl);
+	      locate_old_decl (olddecl);
+	      return false;
+	    }
+	  /* Only record if we are seeing either of these for the first
+	     time.  */
+	  bool record = (!DECL_FUNCTION_VERSIONED (newdecl)
+			 || !DECL_FUNCTION_VERSIONED (olddecl));
+
+	  maybe_mark_function_versioned (newdecl);
+	  maybe_mark_function_versioned (olddecl);
+
+	  if (record)
+	    cgraph_node::record_function_versions (olddecl, newdecl);
+	}
+
+      else if (DECL_INITIAL (newdecl))
 	{
 	  if (DECL_INITIAL (olddecl))
 	    {
@@ -3191,6 +3240,14 @@  duplicate_decls (tree newdecl, tree olddecl)
       return false;
     }
 
+  /* If both new and old are Function Multi Versioned functions then they are
+     not duplicates.  */
+  if (TREE_CODE (newdecl) == FUNCTION_DECL
+      && TREE_CODE (olddecl) == FUNCTION_DECL
+      && DECL_FUNCTION_VERSIONED (newdecl)
+      && DECL_FUNCTION_VERSIONED (olddecl))
+    return false;
+
   merge_decls (newdecl, olddecl, newtype, oldtype);
 
   /* The NEWDECL will no longer be needed.
@@ -13686,6 +13743,10 @@  c_parse_final_cleanups (void)
     c_write_global_declarations_1 (BLOCK_VARS (DECL_INITIAL (t)));
   c_write_global_declarations_1 (BLOCK_VARS (ext_block));
 
+  /* Call this to set cpp_implicit_aliases_done on all nodes.  This is
+     important for function multiversioning aliases to get resolved.  */
+  symtab->process_same_body_aliases ();
+
   if (!in_lto_p)
     free_attr_access_data ();
 
diff --git a/gcc/calls.cc b/gcc/calls.cc
index c5c26f65280..09676a40fc8 100644
--- a/gcc/calls.cc
+++ b/gcc/calls.cc
@@ -5386,3 +5386,26 @@  cxx17_empty_base_field_p (const_tree field)
 	  && RECORD_OR_UNION_TYPE_P (TREE_TYPE (field))
 	  && !lookup_attribute ("no_unique_address", DECL_ATTRIBUTES (field)));
 }
+
+/* Returns the decl of the dispatcher function if FN is a function version.  */
+
+tree
+get_c_function_version_dispatcher (tree fn)
+{
+  tree dispatcher_decl = NULL;
+
+  gcc_assert (TREE_CODE (fn) == FUNCTION_DECL
+	      && DECL_FUNCTION_VERSIONED (fn));
+
+  gcc_assert (targetm.get_function_versions_dispatcher);
+  dispatcher_decl = targetm.get_function_versions_dispatcher (fn);
+
+  if (dispatcher_decl == NULL)
+    {
+      error_at (input_location, "use of multiversioned function "
+				"without a default");
+      return NULL;
+    }
+
+  return dispatcher_decl;
+}
diff --git a/gcc/calls.h b/gcc/calls.h
index 464a4e34e33..aa46853ba63 100644
--- a/gcc/calls.h
+++ b/gcc/calls.h
@@ -134,5 +134,6 @@  extern void maybe_complain_about_tail_call (tree, const char *);
 
 extern rtx rtx_for_static_chain (const_tree, bool);
 extern bool cxx17_empty_base_field_p (const_tree);
+extern tree get_c_function_version_dispatcher (tree fn);
 
 #endif // GCC_CALLS_H
diff --git a/gcc/testsuite/g++.target/aarch64/mv-symbols6.C b/gcc/testsuite/g++.target/aarch64/mv-symbols6.C
new file mode 100644
index 00000000000..52105449e4a
--- /dev/null
+++ b/gcc/testsuite/g++.target/aarch64/mv-symbols6.C
@@ -0,0 +1,16 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+__attribute__((target_version("default")))
+int foo ()
+{
+  return 1;
+}
+
+/* It is not overly clear what the correct behaviour is in this case.
+   This test serves more as a test of consistency for this case rather
+   than a test of correctness.  */
+
+/* { dg-final { scan-assembler-times "\n_Z3foov:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n_Z3foov\.default:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\n_Z3foov\.resolver:\n" 0 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/mv-1.c b/gcc/testsuite/gcc.target/aarch64/mv-1.c
new file mode 100644
index 00000000000..60d4985fec3
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mv-1.c
@@ -0,0 +1,39 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+__attribute__((target_version("default")))
+int foo ()
+{
+  return 1;
+}
+
+__attribute__((target_version("rng")))
+int foo ()
+{
+  return 1;
+}
+
+__attribute__((target_version("flagm")))
+int foo ()
+{
+  return 1;
+}
+
+__attribute__((target_version("rng+flagm")))
+int foo ()
+{
+  return 1;
+}
+
+int bar()
+{
+  return foo ();
+}
+
+/* Check usage of the first two FMV features, in case of off-by-one errors.  */
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mrng:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._MrngMflagm:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mflagm:\n" 1 } } */
+
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/mv-symbols1.c b/gcc/testsuite/gcc.target/aarch64/mv-symbols1.c
new file mode 100644
index 00000000000..b7a7bc2147a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mv-symbols1.c
@@ -0,0 +1,37 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+// Basic case of fmv correctness with all functions and use in one TU. 
+
+__attribute__((target_version("default")))
+int foo ()
+{
+  return 1;
+}
+
+__attribute__((target_version("dotprod")))
+int foo ()
+{
+  return 3;
+}
+__attribute__((target_version("sve+sve2")))
+int foo ()
+{
+  return 5;
+}
+
+int bar()
+{
+  return foo ();
+}
+
+/* When updating any of the symbol names in these tests, make sure to also
+   update any tests for their absence in mv-symbolsN.C */
+
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mdotprod:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._MsveMsve2:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\tbl\tfoo\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.type\tfoo, %gnu_indirect_function\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.set\tfoo,foo\.resolver\n" 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/mv-symbols2.c b/gcc/testsuite/gcc.target/aarch64/mv-symbols2.c
new file mode 100644
index 00000000000..dfa9570da65
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mv-symbols2.c
@@ -0,0 +1,28 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+// FMV correctness with definitions but no call
+
+__attribute__((target_version("default")))
+int foo ()
+{
+  return 1;
+}
+
+__attribute__((target_version("dotprod")))
+int foo ()
+{
+  return 3;
+}
+__attribute__((target_version("sve+sve2")))
+int foo ()
+{
+  return 5;
+}
+
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mdotprod:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._MsveMsve2:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\n\t\.type\tfoo, %gnu_indirect_function\n" 0 } } */
+/* { dg-final { scan-assembler-times "\n\t\.set\tfoo,foo\.resolver\n" 0 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/mv-symbols3.c b/gcc/testsuite/gcc.target/aarch64/mv-symbols3.c
new file mode 100644
index 00000000000..c94610ab2da
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mv-symbols3.c
@@ -0,0 +1,26 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+// FMV correctness with declarations but no implementation
+
+__attribute__((target_version("default")))
+int foo ();
+
+__attribute__((target_version("dotprod")))
+int foo ();
+
+__attribute__((target_version("sve+sve2")))
+int foo ();
+
+int bar()
+{
+  return foo ();
+}
+
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mdotprod:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._MsveMsve2:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\tbl\tfoo\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.type\tfoo, %gnu_indirect_function\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.set\tfoo,foo\.resolver\n" 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/mv-symbols4.c b/gcc/testsuite/gcc.target/aarch64/mv-symbols4.c
new file mode 100644
index 00000000000..25469d20c18
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mv-symbols4.c
@@ -0,0 +1,29 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+// FMV correctness with a default implementation and declarations of other versions
+
+__attribute__((target_version("default")))
+int foo ()
+{
+  return 1;
+}
+
+__attribute__((target_version("dotprod")))
+int foo ();
+
+__attribute__((target_version("sve+sve2")))
+int foo ();
+
+int bar()
+{
+  return foo ();
+}
+
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mdotprod:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._MsveMsve2:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\tbl\tfoo\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.type\tfoo, %gnu_indirect_function\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.set\tfoo,foo\.resolver\n" 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/mv-symbols5.c b/gcc/testsuite/gcc.target/aarch64/mv-symbols5.c
new file mode 100644
index 00000000000..95fa72583bb
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mv-symbols5.c
@@ -0,0 +1,35 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+// FMV correctness with default declaration, and implementations of other 
+// versions.
+
+__attribute__((target_version("default")))
+int foo ();
+
+__attribute__((target_version("dotprod")))
+int foo ()
+{
+  return 3;
+}
+__attribute__((target_version("sve+sve2")))
+int foo ()
+{
+  return 5;
+}
+
+int bar()
+{
+  return foo ();
+}
+
+/* When updating any of the symbol names in these tests, make sure to also
+   update any tests for their absence in mvc-symbolsN.C */
+
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mdotprod:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._MsveMsve2:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\tbl\tfoo\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.type\tfoo, %gnu_indirect_function\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.set\tfoo,foo\.resolver\n" 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/mv-symbols6.c b/gcc/testsuite/gcc.target/aarch64/mv-symbols6.c
new file mode 100644
index 00000000000..8080502a4a4
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mv-symbols6.c
@@ -0,0 +1,17 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+__attribute__((target_version("default")))
+int foo ()
+{
+  return 1;
+}
+
+
+/* It is not overly clear what the correct behaviour is in this case.
+   This test serves more as a test of consistency for this case rather
+   than a test of correctness.  */
+
+/* { dg-final { scan-assembler-times "\nfoo:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 0 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/mvc-symbols1.c b/gcc/testsuite/gcc.target/aarch64/mvc-symbols1.c
new file mode 100644
index 00000000000..4662fbbef57
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mvc-symbols1.c
@@ -0,0 +1,25 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+__attribute__((target_clones("default", "dotprod", "sve+sve2")))
+int foo ()
+{
+  return 1;
+}
+
+int bar()
+{
+  return foo ();
+}
+
+
+/* When updating any of the symbol names in these tests, make sure to also
+   update any tests for their absence in mvc-symbolsN.C */
+
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mdotprod:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._MsveMsve2:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\tbl\tfoo\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.type\tfoo, %gnu_indirect_function\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.set\tfoo,foo\.resolver\n" 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/mvc-symbols2.c b/gcc/testsuite/gcc.target/aarch64/mvc-symbols2.c
new file mode 100644
index 00000000000..112a350e2f7
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mvc-symbols2.c
@@ -0,0 +1,16 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+__attribute__((target_clones("default", "dotprod", "sve+sve2")))
+int foo ()
+{
+  return 1;
+}
+
+
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mdotprod:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._MsveMsve2:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.type\tfoo, %gnu_indirect_function\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.set\tfoo,foo\.resolver\n" 1 } } */
diff --git a/gcc/testsuite/gcc.target/aarch64/mvc-symbols3.c b/gcc/testsuite/gcc.target/aarch64/mvc-symbols3.c
new file mode 100644
index 00000000000..c681fb5b0a6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mvc-symbols3.c
@@ -0,0 +1,19 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+__attribute__((target_clones("default", "dotprod", "sve+sve2")))
+int foo ();
+
+int bar()
+{
+  return foo ();
+}
+
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mdotprod:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._MsveMsve2:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\tbl\tfoo\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.type\tfoo, %gnu_indirect_function\n" 1 } } */
+/* { dg-final { scan-assembler-times "\n\t\.set\tfoo,foo\.resolver\n" 1 } } */
+
diff --git a/gcc/testsuite/gcc.target/aarch64/mvc-symbols4.c b/gcc/testsuite/gcc.target/aarch64/mvc-symbols4.c
new file mode 100644
index 00000000000..81707552ee3
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/mvc-symbols4.c
@@ -0,0 +1,12 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+__attribute__((target_clones("default", "dotprod", "sve+sve2")))
+int foo ();
+
+/* { dg-final { scan-assembler-times "\nfoo\.default:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._Mdotprod:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\._MsveMsve2:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\nfoo\.resolver:\n" 0 } } */
+/* { dg-final { scan-assembler-times "\n\t\.type\tfoo, %gnu_indirect_function\n" 0 } } */
+/* { dg-final { scan-assembler-times "\n\t\.set\tfoo,foo\.resolver\n" 0 } } */