Add new HSeqStringGetChar instruction.

src/arm/lithium-codegen-arm.cc

Index: src/arm/lithium-codegen-arm.cc
diff --git a/src/arm/lithium-codegen-arm.cc b/src/arm/lithium-codegen-arm.cc
index 8eca27d77d9427f5c4fa58ae0d58e8cf4956b28c..c9008c221320fbe8cb732bd20d81d7c3e59d4767 100644
--- a/src/arm/lithium-codegen-arm.cc
+++ b/src/arm/lithium-codegen-arm.cc
@@ -1948,6 +1948,34 @@ MemOperand LCodeGen::BuildSeqStringOperand(Register string,
 }
 
 
+void LCodeGen::DoSeqStringGetChar(LSeqStringGetChar* instr) {
+  String::Encoding encoding = instr->hydrogen()->encoding();
+  Register string = ToRegister(instr->string());
+  Register result = ToRegister(instr->result());
+
+  if (FLAG_debug_code) {
+    Register scratch = scratch0();
+    __ ldr(scratch, FieldMemOperand(string, HeapObject::kMapOffset));
+    __ ldrb(scratch, FieldMemOperand(scratch, Map::kInstanceTypeOffset));
+
+    __ and_(scratch, scratch,
+            Operand(kStringRepresentationMask | kStringEncodingMask));
+    static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
+    static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
+    __ cmp(scratch, Operand(encoding == String::ONE_BYTE_ENCODING

[Sven Panne, 2013/11/07 12:45:14]

Hmmm, a pattern like this comes up several times and all this copy-n-paste is
not really nice. Things would be much nicer if String::Encoding was not an
old-skool enum, but a real class. Then we could have something like
Encoding::ToTag(), but this is probably just OO dreaming... :-/

+                            ? one_byte_seq_type : two_byte_seq_type));
+    __ Check(eq, kUnexpectedStringType);
+  }
+
+  MemOperand operand = BuildSeqStringOperand(string, instr->index(), encoding);
+  if (encoding == String::ONE_BYTE_ENCODING) {

[Sven Panne, 2013/11/07 12:45:14]

This would be nicer with the upcoming "Load" and a yet-to-be written
Encoding::ToRepresentation(). :-)

+    __ ldrb(result, operand);
+  } else {
+    __ ldrh(result, operand);
+  }
+}
+
+
 void LCodeGen::DoSeqStringSetChar(LSeqStringSetChar* instr) {
   String::Encoding encoding = instr->hydrogen()->encoding();
   Register string = ToRegister(instr->string());