Clobber non-live temporaries on some paths involving a possible slow-path allocation.

runtime/vm/intermediate_language_ia32.cc

Index: runtime/vm/intermediate_language_ia32.cc
diff --git a/runtime/vm/intermediate_language_ia32.cc b/runtime/vm/intermediate_language_ia32.cc
index 6a8e1b48cf903224f983d4ada849bad14e6524c4..b40fda4f6f040cd7636a1f25a6c346fff052abad 100644
--- a/runtime/vm/intermediate_language_ia32.cc
+++ b/runtime/vm/intermediate_language_ia32.cc
@@ -1882,6 +1882,9 @@ void StoreInstanceFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
       locs()->live_registers()->Add(locs()->in(1));
     }
 
+    // Manually preserve temp which could be clobbered on the slow path.
+    locs()->live_registers()->Add(locs()->temp(0));

[Vyacheslav Egorov (Google), 2014/12/09 17:49:46]

Actually I have been looking at this code and it does not seem like temp(0) is
live across allocation  slow path so there is no need to preserve it. 

temp(0) is used as allocation result and overwritten

[zerny-google, 2014/12/10 09:49:15]

Your right, the updated patch set won't clobber temp. With patch-set 1, temp was
clobbered on the fast path (via AllocateOnFailure) in with the box_reg value
from EnsureMutableBox would be lost.

+
     {
       __ Bind(&store_double);
       EnsureMutableBox(compiler,
@@ -3800,6 +3803,9 @@ void LoadCodeUnitsInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
     } else {
       // If the value cannot fit in a smi then allocate a mint box for it.
       Register temp = locs()->temp(0).reg();
+      // Temp register needs to be manually preserved on allocation slow-path.
+      locs()->live_registers()->Add(locs()->temp(0), kUnboxedInt32);
+
       ASSERT(temp != result);
       __ MoveRegister(temp, result);
       __ SmiTag(result);