Irregexp: Added derived knowledge of whether we are at the start of input.

src/regexp-macro-assembler-ia32.cc

Index: src/regexp-macro-assembler-ia32.cc
diff --git a/src/regexp-macro-assembler-ia32.cc b/src/regexp-macro-assembler-ia32.cc
index e58177c3a52735d71ae8e92b6e687114d4a2fe81..c5380b3e7374f697f2192da89a5a2870608e1361 100644
--- a/src/regexp-macro-assembler-ia32.cc
+++ b/src/regexp-macro-assembler-ia32.cc
@@ -636,7 +636,7 @@ Handle<Object> RegExpMacroAssemblerIA32::GetCode(Handle<String> source) {
   __ push(esi);
   __ push(edi);
   __ push(ebx);  // Callee-save on MacOS.
-  __ push(Immediate(0));  // Make room for input start minus one
+  __ push(Immediate(0));  // Make room for "input start - 1" constant.
 
   // Check if we have space on the stack for registers.
   Label retry_stack_check;