Put live register bits in stackmaps.

runtime/vm/flow_graph_compiler.cc

Index: runtime/vm/flow_graph_compiler.cc
diff --git a/runtime/vm/flow_graph_compiler.cc b/runtime/vm/flow_graph_compiler.cc
index a9361c12cb132519d4ba68cf76f0d01d89935e3e..459c3075a3872b6535e6f7a21a3216a95ac566cd 100644
--- a/runtime/vm/flow_graph_compiler.cc
+++ b/runtime/vm/flow_graph_compiler.cc
@@ -9,6 +9,7 @@
 #include "vm/dart_entry.h"
 #include "vm/debugger.h"
 #include "vm/deopt_instructions.h"
+#include "vm/flow_graph_allocator.h"
 #include "vm/il_printer.h"
 #include "vm/intrinsifier.h"
 #include "vm/locations.h"
@@ -252,8 +253,43 @@ void FlowGraphCompiler::RecordSafepoint(LocationSummary* locs) {
   if (is_optimizing()) {
     BitmapBuilder* bitmap = locs->stack_bitmap();
     ASSERT(bitmap != NULL);
+    ASSERT(bitmap->Length() <= StackSize());
+    // Pad the bitmap out to describe all the spill slots.
     bitmap->SetLength(StackSize());
-    stackmap_table_builder_->AddEntry(assembler()->CodeSize(), bitmap);
+
+    // Slow path code can have registers at the safepoint.
+    if (!locs->always_calls()) {
+      // Mark the bits in the stack map in the same order we push registers

[Vyacheslav Egorov (Google), 2012/08/30 09:24:35]

this does not actually match with that order: when we store xmm registers xmm0
comes at the top (if live), but here last one comes at the top.

[Kevin Millikin (Google), 2012/08/30 10:02:21]

You're right and it's a bit fishy.  I've made it match.

+      // in slow path code (see FlowGraphCompiler::SaveLiveRegisters).
+      RegisterSet* regs = locs->live_registers();
+      if (regs->xmm_regs_count() > 0) {
+        // Denote XMM registers  with 0 bits in the  stackmap.  Based on the
+        // assumption that  there are normally few live  XMM registers, this

[Vyacheslav Egorov (Google), 2012/08/30 09:24:35]

s/live  XMM/live XMM/

[Kevin Millikin (Google), 2012/08/30 10:02:21]

You don't like the fully justified comments?

+        // encoding is simpler and roughly  as compact as storing a separate
+        // count of XMM registers.
+        for (intptr_t i = 0; i < kNumberOfXmmRegisters; ++i) {
+          XmmRegister reg = static_cast<XmmRegister>(i);
+          if (regs->ContainsXmmRegister(reg)) {
+            for (intptr_t j = 0;
+                 j < FlowGraphAllocator::kDoubleSpillSlotFactor;
+                 ++j) {
+              bitmap->Set(bitmap->Length(), false);
+            }
+          }
+        }
+      }
+      for (intptr_t i = 0; i < kNumberOfCpuRegisters; ++i) {
+        Register reg = static_cast<Register>(i);
+        if (locs->live_registers()->ContainsRegister(reg)) {
+          bitmap->Set(bitmap->Length(), true);
+        }
+      }
+    }
+
+    intptr_t register_bit_count = bitmap->Length() - StackSize();
+    stackmap_table_builder_->AddEntry(assembler()->CodeSize(),
+                                      bitmap,
+                                      register_bit_count);
   }
 }