Revert of Experimental support for RegExp lookbehind.

src/regexp/mips/regexp-macro-assembler-mips.cc

Index: src/regexp/mips/regexp-macro-assembler-mips.cc
diff --git a/src/regexp/mips/regexp-macro-assembler-mips.cc b/src/regexp/mips/regexp-macro-assembler-mips.cc
index f1fc4e7dbd39222edc150b5424a0e2b3b633aa19..77f09917c06026535608c0cae952f2546ef4579f 100644
--- a/src/regexp/mips/regexp-macro-assembler-mips.cc
+++ b/src/regexp/mips/regexp-macro-assembler-mips.cc
@@ -181,17 +181,26 @@
 
 
 void RegExpMacroAssemblerMIPS::CheckAtStart(Label* on_at_start) {
-  __ lw(a1, MemOperand(frame_pointer(), kStringStartMinusOne));
-  __ Addu(a0, current_input_offset(), Operand(-char_size()));
+  Label not_at_start;
+  // Did we start the match at the start of the string at all?
+  __ lw(a0, MemOperand(frame_pointer(), kStartIndex));
+  BranchOrBacktrack(&not_at_start, ne, a0, Operand(zero_reg));
+
+  // If we did, are we still at the start of the input?
+  __ lw(a1, MemOperand(frame_pointer(), kInputStart));
+  __ Addu(a0, end_of_input_address(), Operand(current_input_offset()));
   BranchOrBacktrack(on_at_start, eq, a0, Operand(a1));
-}
-
-
-void RegExpMacroAssemblerMIPS::CheckNotAtStart(int cp_offset,
-                                               Label* on_not_at_start) {
-  __ lw(a1, MemOperand(frame_pointer(), kStringStartMinusOne));
-  __ Addu(a0, current_input_offset(),
-          Operand(-char_size() + cp_offset * char_size()));
+  __ bind(&not_at_start);
+}
+
+
+void RegExpMacroAssemblerMIPS::CheckNotAtStart(Label* on_not_at_start) {
+  // Did we start the match at the start of the string at all?
+  __ lw(a0, MemOperand(frame_pointer(), kStartIndex));
+  BranchOrBacktrack(on_not_at_start, ne, a0, Operand(zero_reg));
+  // If we did, are we still at the start of the input?
+  __ lw(a1, MemOperand(frame_pointer(), kInputStart));
+  __ Addu(a0, end_of_input_address(), Operand(current_input_offset()));
   BranchOrBacktrack(on_not_at_start, ne, a0, Operand(a1));
 }
 
@@ -214,26 +223,20 @@
 
 
 void RegExpMacroAssemblerMIPS::CheckNotBackReferenceIgnoreCase(
-    int start_reg, bool read_backward, Label* on_no_match) {
+    int start_reg,
+    Label* on_no_match) {
   Label fallthrough;
   __ lw(a0, register_location(start_reg));  // Index of start of capture.
   __ lw(a1, register_location(start_reg + 1));  // Index of end of capture.
   __ Subu(a1, a1, a0);  // Length of capture.
 
-  // At this point, the capture registers are either both set or both cleared.
-  // If the capture length is zero, then the capture is either empty or cleared.
-  // Fall through in both cases.
+  // If length is zero, either the capture is empty or it is not participating.
+  // In either case succeed immediately.
   __ Branch(&fallthrough, eq, a1, Operand(zero_reg));
 
-  if (read_backward) {
-    __ lw(t0, MemOperand(frame_pointer(), kStringStartMinusOne));
-    __ Addu(t0, t0, a1);
-    BranchOrBacktrack(on_no_match, le, current_input_offset(), Operand(t0));
-  } else {
-    __ Addu(t5, a1, current_input_offset());
-    // Check that there are enough characters left in the input.
-    BranchOrBacktrack(on_no_match, gt, t5, Operand(zero_reg));
-  }
+  __ Addu(t5, a1, current_input_offset());
+  // Check that there are enough characters left in the input.
+  BranchOrBacktrack(on_no_match, gt, t5, Operand(zero_reg));
 
   if (mode_ == LATIN1) {
     Label success;
@@ -244,9 +247,6 @@
     // a1 - length of capture.
     __ Addu(a0, a0, Operand(end_of_input_address()));
     __ Addu(a2, end_of_input_address(), Operand(current_input_offset()));
-    if (read_backward) {
-      __ Subu(a2, a2, Operand(a1));
-    }
     __ Addu(a1, a0, Operand(a1));
 
     // a0 - Address of start of capture.
@@ -285,12 +285,6 @@
     __ bind(&success);
     // Compute new value of character position after the matched part.
     __ Subu(current_input_offset(), a2, end_of_input_address());
-    if (read_backward) {
-      __ lw(t0, register_location(start_reg));  // Index of start of capture.
-      __ lw(t5, register_location(start_reg + 1));  // Index of end of capture.
-      __ Addu(current_input_offset(), current_input_offset(), Operand(t0));
-      __ Subu(current_input_offset(), current_input_offset(), Operand(t5));
-    }
   } else {
     DCHECK(mode_ == UC16);
     // Put regexp engine registers on stack.
@@ -319,9 +313,6 @@
     __ mov(s3, a1);
     // Address of current input position.
     __ Addu(a1, current_input_offset(), Operand(end_of_input_address()));
-    if (read_backward) {
-      __ Subu(a1, a1, Operand(s3));
-    }
     // Isolate.
     __ li(a3, Operand(ExternalReference::isolate_address(masm_->isolate())));
 
@@ -339,21 +330,17 @@
 
     // Check if function returned non-zero for success or zero for failure.
     BranchOrBacktrack(on_no_match, eq, v0, Operand(zero_reg));
-    // On success, advance position by length of capture.
-    if (read_backward) {
-      __ Subu(current_input_offset(), current_input_offset(), Operand(s3));
-    } else {
-      __ Addu(current_input_offset(), current_input_offset(), Operand(s3));
-    }
+    // On success, increment position by length of capture.
+    __ Addu(current_input_offset(), current_input_offset(), Operand(s3));
   }
 
   __ bind(&fallthrough);
 }
 
 
-void RegExpMacroAssemblerMIPS::CheckNotBackReference(int start_reg,
-                                                     bool read_backward,
-                                                     Label* on_no_match) {
+void RegExpMacroAssemblerMIPS::CheckNotBackReference(
+    int start_reg,
+    Label* on_no_match) {
   Label fallthrough;
   Label success;
 
@@ -361,35 +348,17 @@
   __ lw(a0, register_location(start_reg));
   __ lw(a1, register_location(start_reg + 1));
   __ Subu(a1, a1, a0);  // Length to check.
-
-  // At this point, the capture registers are either both set or both cleared.
-  // If the capture length is zero, then the capture is either empty or cleared.
-  // Fall through in both cases.
-  __ Branch(&fallthrough, le, a1, Operand(zero_reg));
-
-  if (read_backward) {
-    __ lw(t0, MemOperand(frame_pointer(), kStringStartMinusOne));
-    __ Addu(t0, t0, a1);
-    BranchOrBacktrack(on_no_match, le, current_input_offset(), Operand(t0));
-  } else {
-    __ Addu(t5, a1, current_input_offset());
-    // Check that there are enough characters left in the input.
-    BranchOrBacktrack(on_no_match, gt, t5, Operand(zero_reg));
-  }
-
-  // a0 - offset of start of capture.
-  // a1 - length of capture.
+  // Succeed on empty capture (including no capture).
+  __ Branch(&fallthrough, eq, a1, Operand(zero_reg));
+
+  __ Addu(t5, a1, current_input_offset());
+  // Check that there are enough characters left in the input.
+  BranchOrBacktrack(on_no_match, gt, t5, Operand(zero_reg));
+
+  // Compute pointers to match string and capture string.
   __ Addu(a0, a0, Operand(end_of_input_address()));
   __ Addu(a2, end_of_input_address(), Operand(current_input_offset()));
-  if (read_backward) {
-    __ Subu(a2, a2, Operand(a1));
-  }
-  __ Addu(a1, a0, Operand(a1));
-
-  // a0 - Address of start of capture.
-  // a1 - Address of end of capture.
-  // a2 - Address of current input position.
-
+  __ Addu(a1, a1, Operand(a0));
 
   Label loop;
   __ bind(&loop);
@@ -410,12 +379,6 @@
 
   // Move current character position to position after match.
   __ Subu(current_input_offset(), a2, end_of_input_address());
-  if (read_backward) {
-    __ lw(t0, register_location(start_reg));      // Index of start of capture.
-    __ lw(t5, register_location(start_reg + 1));  // Index of end of capture.
-    __ Addu(current_input_offset(), current_input_offset(), Operand(t0));
-    __ Subu(current_input_offset(), current_input_offset(), Operand(t5));
-  }
   __ bind(&fallthrough);
 }
 
@@ -636,7 +599,7 @@
     __ Addu(frame_pointer(), sp, Operand(4 * kPointerSize));
     __ mov(a0, zero_reg);
     __ push(a0);  // Make room for success counter and initialize it to 0.
-    __ push(a0);  // Make room for "string start - 1" constant.
+    __ push(a0);  // Make room for "position - 1" constant (value irrelevant).
 
     // Check if we have space on the stack for registers.
     Label stack_limit_hit;
@@ -679,7 +642,7 @@
     __ Subu(a0, a0, t5);
     // Store this value in a local variable, for use when clearing
     // position registers.
-    __ sw(a0, MemOperand(frame_pointer(), kStringStartMinusOne));
+    __ sw(a0, MemOperand(frame_pointer(), kInputStartMinusOne));
 
     // Initialize code pointer register
     __ li(code_pointer(), Operand(masm_->CodeObject()), CONSTANT_SIZE);
@@ -788,7 +751,7 @@
         __ sw(a2, MemOperand(frame_pointer(), kRegisterOutput));
 
         // Prepare a0 to initialize registers with its value in the next run.
-        __ lw(a0, MemOperand(frame_pointer(), kStringStartMinusOne));
+        __ lw(a0, MemOperand(frame_pointer(), kInputStartMinusOne));
 
         if (global_with_zero_length_check()) {
           // Special case for zero-length matches.
@@ -942,13 +905,10 @@
                                                     Label* on_end_of_input,
                                                     bool check_bounds,
                                                     int characters) {
+  DCHECK(cp_offset >= -1);      // ^ and \b can look behind one character.
   DCHECK(cp_offset < (1<<30));  // Be sane! (And ensure negation works).
   if (check_bounds) {
-    if (cp_offset >= 0) {
-      CheckPosition(cp_offset + characters - 1, on_end_of_input);
-    } else {
-      CheckPosition(cp_offset, on_end_of_input);
-    }
+    CheckPosition(cp_offset + characters - 1, on_end_of_input);
   }
   LoadCurrentCharacterUnchecked(cp_offset, characters);
 }
@@ -1056,7 +1016,7 @@
 
 void RegExpMacroAssemblerMIPS::ClearRegisters(int reg_from, int reg_to) {
   DCHECK(reg_from <= reg_to);
-  __ lw(a0, MemOperand(frame_pointer(), kStringStartMinusOne));
+  __ lw(a0, MemOperand(frame_pointer(), kInputStartMinusOne));
   for (int reg = reg_from; reg <= reg_to; reg++) {
     __ sw(a0, register_location(reg));
   }
@@ -1169,14 +1129,10 @@
 
 void RegExpMacroAssemblerMIPS::CheckPosition(int cp_offset,
                                              Label* on_outside_input) {
-  if (cp_offset >= 0) {
-    BranchOrBacktrack(on_outside_input, ge, current_input_offset(),
-                      Operand(-cp_offset * char_size()));
-  } else {
-    __ lw(a1, MemOperand(frame_pointer(), kStringStartMinusOne));
-    __ Addu(a0, current_input_offset(), Operand(cp_offset * char_size()));
-    BranchOrBacktrack(on_outside_input, le, a0, Operand(a1));
-  }
+  BranchOrBacktrack(on_outside_input,
+                    ge,
+                    current_input_offset(),
+                    Operand(-cp_offset * char_size()));
 }