Specialize breakpoint stubs by set of live registers of the stubs they are intercepting.

runtime/vm/debugger_x64.cc

Index: runtime/vm/debugger_x64.cc
diff --git a/runtime/vm/debugger_x64.cc b/runtime/vm/debugger_x64.cc
index 171a0b39d00112d25404a152e6261b9b731e6d7a..54565f156940374c5ec7c39d088d0917b2e92954 100644
--- a/runtime/vm/debugger_x64.cc
+++ b/runtime/vm/debugger_x64.cc
@@ -55,15 +55,33 @@ void CodeBreakpoint::PatchCode() {
     WritableInstructionsScope writable(instrs.EntryPoint(), instrs.size());
     switch (breakpoint_kind_) {
       case PcDescriptors::kIcCall:
-      case PcDescriptors::kUnoptStaticCall:
-      case PcDescriptors::kRuntimeCall:
+      case PcDescriptors::kUnoptStaticCall: {
+        int32_t offset = CodePatcher::GetPoolOffsetAt(pc_);
+        ASSERT((offset > 0) && ((offset % 8) == 7));
+        saved_value_ = static_cast<uword>(offset);
+        const uint32_t stub_offset =
+            InstructionPattern::OffsetFromPPIndex(
+                Assembler::kICCallBreakpointCPIndex);
+        CodePatcher::SetPoolOffsetAt(pc_, stub_offset);

[Florian Schneider, 2014/06/30 09:00:40]

Why use the constant pool here?

So ARM and MIPS have a constant pool, but don't use it here, where as x64 and
arm64 do use it. I find this inconsistency suboptimal unless there are very good
reasons to use the constant pool here.

[rmacnak, 2014/07/01 01:08:51]

Not sure. Was introduced in https://codereview.chromium.org/131853006/.

[rmacnak, 2014/07/09 21:23:46]

The difference is x64/arm64 reuse constant pool entries. A stub can be shared
between multiple call sites, and a breakpoint might be set for only one of them,
so we can't patch the pool entry.

+        break;
+      }
       case PcDescriptors::kClosureCall: {
         int32_t offset = CodePatcher::GetPoolOffsetAt(pc_);
         ASSERT((offset > 0) && ((offset % 8) == 7));
         saved_value_ = static_cast<uword>(offset);
         const uint32_t stub_offset =
             InstructionPattern::OffsetFromPPIndex(
-                Assembler::kBreakpointRuntimeCPIndex);
+                Assembler::kClosureCallBreakpointCPIndex);
+        CodePatcher::SetPoolOffsetAt(pc_, stub_offset);
+        break;
+      }
+      case PcDescriptors::kRuntimeCall: {
+        int32_t offset = CodePatcher::GetPoolOffsetAt(pc_);
+        ASSERT((offset > 0) && ((offset % 8) == 7));
+        saved_value_ = static_cast<uword>(offset);
+        const uint32_t stub_offset =
+            InstructionPattern::OffsetFromPPIndex(
+                Assembler::kRuntimeCallBreakpointCPIndex);
         CodePatcher::SetPoolOffsetAt(pc_, stub_offset);
         break;
       }