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

runtime/vm/stub_code_arm.cc

Index: runtime/vm/stub_code_arm.cc
diff --git a/runtime/vm/stub_code_arm.cc b/runtime/vm/stub_code_arm.cc
index 91b2a3bc9e0651fe60a0a0f9a59ca7ad880416ff..fe60d63b6a3c32cc7771aa63ad1941f2a64cdcac 100644
--- a/runtime/vm/stub_code_arm.cc
+++ b/runtime/vm/stub_code_arm.cc
@@ -46,7 +46,6 @@ void StubCode::GenerateCallToRuntimeStub(Assembler* assembler) {
   __ mov(IP, Operand(0));
   __ Push(IP);  // Push 0 for the PC marker.
   __ EnterFrame((1 << FP) | (1 << LR), 0);
-  __ SmiUntag(R4);
 
   // Load current Isolate pointer from Context structure into R0.
   __ ldr(R0, FieldAddress(CTX, Context::isolate_offset()));
@@ -1530,7 +1529,23 @@ void StubCode::GenerateLazyCompileStub(Assembler* assembler) {
 }
 
 
-void StubCode::GenerateBreakpointRuntimeStub(Assembler* assembler) {
+// R5: Contains an ICData.
+void StubCode::GenerateICCallBreakpointStub(Assembler* assembler) {
+  __ EnterStubFrame();
+  __ LoadImmediate(R0, reinterpret_cast<intptr_t>(Object::null()));
+  // Preserve arguments descriptor and make room for result.
+  __ PushList((1 << R0) | (1 << R5));
+  __ CallRuntime(kBreakpointRuntimeHandlerRuntimeEntry, 0);
+  __ PopList((1 << R0) | (1 << R5));
+  __ LeaveStubFrame();
+  __ bx(R0);
+}
+
+
+// R5: Contains Smi 0 (need to preserve a GC-safe value for the lazy compile
+// stub).
+// R4: Contains an arguments descriptor.
+void StubCode::GenerateClosureCallBreakpointStub(Assembler* assembler) {
   __ EnterStubFrame();
   __ LoadImmediate(R0, reinterpret_cast<intptr_t>(Object::null()));
   // Preserve arguments descriptor and make room for result.
@@ -1541,6 +1556,22 @@ void StubCode::GenerateBreakpointRuntimeStub(Assembler* assembler) {
   __ bx(R0);
 }
 
+// R5: Garbage or function address.
+// R4: Garbage or raw argument count.
+void StubCode::GenerateRuntimeCallBreakpointStub(Assembler* assembler) {
+  __ EnterStubFrame();
+  __ LoadImmediate(R0, reinterpret_cast<intptr_t>(Object::null()));
+  // Preserve arguments descriptor and make room for result.
+  __ AndImmediate(R5, R5, ~kSmiTagMask);
+  __ SmiTag(R4);
+  __ PushList((1 << R0) | (1 << R4) | (1 << R5));

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

Why do you need to preserve R4 and R5 here?

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

Don't I need to preserve them for the original stub?

save r4/5
load r4/5 with values for runtime call BreakpointRuntimeHandler
call
restore r4/5
jump to original stub (r0)

My test passes if they aren't though..

[Florian Schneider, 2014/07/03 19:56:03]

I don't think so.  When doing a code search for kRuntimeCall I only see one
place where it is used: the call to the IdenticalWithNumberCheck stub. R4 and R5
are not used for anything there.

+  __ CallRuntime(kBreakpointRuntimeHandlerRuntimeEntry, 0);
+  __ PopList((1 << R0) | (1 << R4) | (1 << R5));
+  __ SmiUntag(R4);
+  __ LeaveStubFrame();
+  __ bx(R0);
+}
+
 
 // Called only from unoptimized code. All relevant registers have been saved.
 void StubCode::GenerateDebugStepCheckStub(