Capture register clearing on loop iteration

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 7afc46d7d03489574df4575fcf0b9da071af6702..1d6d18663988b0ac3b5464eba90c32fb347976a2 100644
--- a/src/regexp-macro-assembler-ia32.cc
+++ b/src/regexp-macro-assembler-ia32.cc
@@ -928,6 +928,11 @@ void RegExpMacroAssemblerIA32::WriteCurrentPositionToRegister(int reg,
 }
 
 
+void RegExpMacroAssemblerIA32::ClearRegister(int reg) {
+  __ mov(register_location(reg), esi);

[Lasse Reichstein, 2009/01/14 08:38:34]

The esi register does not hold the needed value (one character before the start
of the string) but instead it points to the end of the string.
A cleared register would be seen as captured, with a position at the end of the
string.

Code that, I think, should trigger this:
 var m = /(?:(a)|b)*/.exec("ab");
 // m[1] should be null, it is "".
Otherwise a C-level test should show the difference in returned value for the
capture registers (2 instead of -1).

The correct value is computed in GetCode(), in the entry part, where we
initialize the capture registers. I suggest storing it somewhere safe (e.g., as
a "local variable" in the stack frame) until it's needed.

[Christian Plesner Hansen, 2009/01/14 11:31:35]

Fixed

+}
+
+
 void RegExpMacroAssemblerIA32::WriteStackPointerToRegister(int reg) {
   __ mov(register_location(reg), backtrack_stackpointer());
 }