Explicitly clear out the IC-data register in ExecuteMatch.

runtime/vm/intrinsifier_ia32.cc

Index: runtime/vm/intrinsifier_ia32.cc
diff --git a/runtime/vm/intrinsifier_ia32.cc b/runtime/vm/intrinsifier_ia32.cc
index 713282a339076628770ab103785589c13e68705f..9101614bb185d22c602ba6722fab64a358b28ea4 100644
--- a/runtime/vm/intrinsifier_ia32.cc
+++ b/runtime/vm/intrinsifier_ia32.cc
@@ -2060,7 +2060,7 @@ void Intrinsifier::JSRegExp_ExecuteMatch(Assembler* assembler) {
 
   // Incoming registers:
   // EAX: Function. (Will be loaded with the specialized matcher function.)
-  // ECX: IC-Data. (Will be preserved.)
+  // ECX: Unknown. (Must be GC safe on tail call.)
   // EDX: Arguments descriptor. (Will be preserved.)
 
   // Load the specialized function pointer into EAX. Leverage the fact the
@@ -2076,6 +2076,7 @@ void Intrinsifier::JSRegExp_ExecuteMatch(Assembler* assembler) {
   // in EAX, the argument descriptor in EDX, and IC-Data in ECX.
   static const intptr_t arg_count = RegExpMacroAssembler::kParamCount;
   __ LoadObject(EDX, Array::Handle(ArgumentsDescriptor::New(arg_count)));
+  __ xorl(ECX, ECX);
 
   // Tail-call the function.
   __ movl(EDI, FieldAddress(EAX, Function::instructions_offset()));