Enables per-function far-branches for ARM and MIPS.

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
===================================================================
--- runtime/vm/compiler.cc	(revision 25620)
+++ runtime/vm/compiler.cc	(working copy)
@@ -488,52 +488,75 @@
       }
     }
 
-    Assembler assembler;
-    FlowGraphCompiler graph_compiler(&assembler,
-                                     *flow_graph,
-                                     optimized);
-    {
-      TimerScope timer(FLAG_compiler_stats,
-                       &CompilerStats::graphcompiler_timer,
-                       isolate);
-      graph_compiler.CompileGraph();
-    }
-    {
-      TimerScope timer(FLAG_compiler_stats,
-                       &CompilerStats::codefinalizer_timer,
-                       isolate);
-      const Code& code = Code::Handle(
-          Code::FinalizeCode(function, &assembler, optimized));
-      code.set_is_optimized(optimized);
-      graph_compiler.FinalizePcDescriptors(code);
-      graph_compiler.FinalizeDeoptInfo(code);
-      graph_compiler.FinalizeStackmaps(code);
-      graph_compiler.FinalizeVarDescriptors(code);
-      graph_compiler.FinalizeExceptionHandlers(code);
-      graph_compiler.FinalizeComments(code);
-      graph_compiler.FinalizeStaticCallTargetsTable(code);
+    // First, try to assemble the function using only near branches. If that
+    // fails, we'll longjmp back here, set the needs_far_branches bit in the
+    // function and try again.
+    bool assembled = false;
+    while (!assembled) {
+      const intptr_t prev_deopt_id = isolate->deopt_id();
+      isolate->set_deopt_id(0);
+      LongJump* assembler_old_base = isolate->long_jump_base();
+      LongJump assembler_jump;
+      isolate->set_long_jump_base(&assembler_jump);
+      if (setjmp(*assembler_jump.Set()) == 0) {
+        Assembler assembler(flow_graph->use_far_branches());
+        FlowGraphCompiler graph_compiler(&assembler,
+                                         *flow_graph,
+                                         optimized);
+        {
+          TimerScope timer(FLAG_compiler_stats,
+                           &CompilerStats::graphcompiler_timer,
+                           isolate);
+          graph_compiler.CompileGraph();
+          assembled = true;
+        }
+        {
+          TimerScope timer(FLAG_compiler_stats,
+                           &CompilerStats::codefinalizer_timer,
+                           isolate);
+          const Code& code = Code::Handle(
+              Code::FinalizeCode(function, &assembler, optimized));
+          code.set_is_optimized(optimized);
+          graph_compiler.FinalizePcDescriptors(code);
+          graph_compiler.FinalizeDeoptInfo(code);
+          graph_compiler.FinalizeStackmaps(code);
+          graph_compiler.FinalizeVarDescriptors(code);
+          graph_compiler.FinalizeExceptionHandlers(code);
+          graph_compiler.FinalizeComments(code);
+          graph_compiler.FinalizeStaticCallTargetsTable(code);
 
-      if (optimized) {
-        if (osr_id == Isolate::kNoDeoptId) {
-          CodePatcher::PatchEntry(Code::Handle(function.CurrentCode()));
-          if (FLAG_trace_compiler) {
-            OS::Print("--> patching entry %#"Px"\n",
-                      Code::Handle(function.unoptimized_code()).EntryPoint());
+          if (optimized) {
+            if (osr_id == Isolate::kNoDeoptId) {
+              CodePatcher::PatchEntry(Code::Handle(function.CurrentCode()));
+              if (FLAG_trace_compiler) {
+                OS::Print("--> patching entry %#"Px"\n",
+                    Code::Handle(function.unoptimized_code()).EntryPoint());
+              }
+            }
+            function.SetCode(code);
+
+            for (intptr_t i = 0; i < guarded_fields.length(); i++) {
+              const Field& field = *guarded_fields[i];
+              field.RegisterDependentCode(code);
+            }
+          } else {
+            function.set_unoptimized_code(code);
+            function.SetCode(code);
+            ASSERT(CodePatcher::CodeIsPatchable(code));
           }
         }
-        function.SetCode(code);
+        is_compiled = true;
+      } else {
+        isolate->object_store()->clear_sticky_error();
 
-        for (intptr_t i = 0; i < guarded_fields.length(); i++) {
-          const Field& field = *guarded_fields[i];
-          field.RegisterDependentCode(code);
-        }
-      } else {
-        function.set_unoptimized_code(code);
-        function.SetCode(code);
-        ASSERT(CodePatcher::CodeIsPatchable(code));
+        // If far branches were enabled, assembly should not fail again.
+        ASSERT(!flow_graph->use_far_branches());
+        flow_graph->set_use_far_branches(true);
+        is_compiled = false;
       }
+      isolate->set_long_jump_base(assembler_old_base);
+      isolate->set_deopt_id(prev_deopt_id);
     }
-    is_compiled = true;
   } else {
     // We bailed out.
     Error& bailout_error = Error::Handle(