backend: handle cold attribute

gcc/rust/backend/rust-compile-base.cc

@@ -55,6 +55,7 @@ HIRCompileBase::setup_attributes_on_fndecl (
       bool is_inline = attr.get_path ().as_string ().compare ("inline") == 0;
       bool is_must_use
 	= attr.get_path ().as_string ().compare ("must_use") == 0;
+      bool is_cold = attr.get_path ().as_string ().compare ("cold") == 0;
       if (is_inline)
 	{
 	  handle_inline_attribute_on_fndecl (fndecl, attr);
@@ -63,9 +64,31 @@ HIRCompileBase::setup_attributes_on_fndecl (
 	{
 	  handle_must_use_attribute_on_fndecl (fndecl, attr);
 	}
+      else if (is_cold)
+	{
+	  handle_cold_attribute_on_fndecl (fndecl, attr);
+	}
     }
 }
 
+void
+HIRCompileBase::handle_cold_attribute_on_fndecl (tree fndecl,
+						 const AST::Attribute &attr)
+{
+  // simple #[cold]
+  if (!attr.has_attr_input ())
+    {
+      tree cold = get_identifier ("cold");
+      // this will get handled by the GCC backend later
+      DECL_ATTRIBUTES (fndecl)
+	= tree_cons (cold, NULL_TREE, DECL_ATTRIBUTES (fndecl));
+      return;
+    }
+
+  rust_error_at (attr.get_locus (),
+		 "attribute %<cold%> does not accept any arguments");
+}
+
 void
 HIRCompileBase::handle_inline_attribute_on_fndecl (tree fndecl,
 						   const AST::Attribute &attr)

gcc/rust/backend/rust-compile-base.h

@@ -82,6 +82,9 @@ protected:
   static void handle_inline_attribute_on_fndecl (tree fndecl,
 						 const AST::Attribute &attr);
 
+  static void handle_cold_attribute_on_fndecl (tree fndecl,
+					       const AST::Attribute &attr);
+
   static void handle_must_use_attribute_on_fndecl (tree fndecl,
 						   const AST::Attribute &attr);
 

gcc/rust/util/rust-attributes.cc

@@ -22,11 +22,16 @@ namespace Rust {
 namespace Analysis {
 
 // https://doc.rust-lang.org/stable/nightly-rustc/src/rustc_feature/builtin_attrs.rs.html#248
-static const BuiltinAttrDefinition __definitions[]
+static const BuiltinAttrDefinition __definitions[] = {
-  = {{"inline", CODE_GENERATION},  {"cfg", EXPANSION},
+  {"inline", CODE_GENERATION},
-     {"cfg_attr", EXPANSION},	   {"allow", STATIC_ANALYSIS},
+  {"cold", CODE_GENERATION},
-     {"doc", HIR_LOWERING},	   {"lang", HIR_LOWERING},
+  {"cfg", EXPANSION},
-     {"must_use", STATIC_ANALYSIS}};
+  {"cfg_attr", EXPANSION},
+  {"allow", STATIC_ANALYSIS},
+  {"doc", HIR_LOWERING},
+  {"must_use", STATIC_ANALYSIS},
+  {"lang", HIR_LOWERING},
+};
 
 BuiltinAttributeMappings *
 BuiltinAttributeMappings::get ()

gcc/testsuite/rust/compile/attr_cold.rs

@@ -0,0 +1,12 @@
+// { dg-additional-options "-fdump-tree-gimple }
+#[cold]
+fn cold_function() -> i32 {
+    42
+}
+
+fn main() -> i32 {
+    // { dg-final { scan-tree-dump-times {__attribute__((cdecl, cold))} 1 gimple } }
+    cold_function();
+
+    0
+}