Revert of Experimental support for RegExp lookbehind.

src/regexp/mips64/regexp-macro-assembler-mips64.cc

Index: src/regexp/mips64/regexp-macro-assembler-mips64.cc
diff --git a/src/regexp/mips64/regexp-macro-assembler-mips64.cc b/src/regexp/mips64/regexp-macro-assembler-mips64.cc
index d774b14016b7fcf35eccfd1cb0864446235f982a..869cbc4f2e20398595bb421ad65d6e8c1517685b 100644
--- a/src/regexp/mips64/regexp-macro-assembler-mips64.cc
+++ b/src/regexp/mips64/regexp-macro-assembler-mips64.cc
@@ -61,7 +61,7 @@
  *  - fp[-16] void* input_string (location of a handle containing the string).
  *  - fp[-20] success counter    (only for global regexps to count matches).
  *  - fp[-24] Offset of location before start of input (effectively character
- *            string start - 1). Used to initialize capture registers to a
+ *            position -1). Used to initialize capture registers to a
  *            non-position.
  *  - fp[-28] At start (if 1, we are starting at the start of the
  *    string, otherwise 0)
@@ -91,7 +91,7 @@
  *  - fp[-56] start index        (character index of start).                    kStartIndex
  *  - fp[-64] void* input_string (location of a handle containing the string).  kInputString
  *  - fp[-72] success counter    (only for global regexps to count matches).    kSuccessfulCaptures
- *  - fp[-80] Offset of location before start of input (effectively character   kStringStartMinusOne
+ *  - fp[-80] Offset of location before start of input (effectively character   kInputStartMinusOne
  *            position -1). Used to initialize capture registers to a
  *            non-position.
  *  --------- The following output registers are 32-bit values. ---------
@@ -217,17 +217,26 @@
 
 
 void RegExpMacroAssemblerMIPS::CheckAtStart(Label* on_at_start) {
-  __ ld(a1, MemOperand(frame_pointer(), kStringStartMinusOne));
-  __ Daddu(a0, current_input_offset(), Operand(-char_size()));
+  Label not_at_start;
+  // Did we start the match at the start of the string at all?
+  __ ld(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?
+  __ ld(a1, MemOperand(frame_pointer(), kInputStart));
+  __ Daddu(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) {
-  __ ld(a1, MemOperand(frame_pointer(), kStringStartMinusOne));
-  __ Daddu(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?
+  __ ld(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?
+  __ ld(a1, MemOperand(frame_pointer(), kInputStart));
+  __ Daddu(a0, end_of_input_address(), Operand(current_input_offset()));
   BranchOrBacktrack(on_not_at_start, ne, a0, Operand(a1));
 }
 
@@ -250,26 +259,20 @@
 
 
 void RegExpMacroAssemblerMIPS::CheckNotBackReferenceIgnoreCase(
-    int start_reg, bool read_backward, Label* on_no_match) {
+    int start_reg,
+    Label* on_no_match) {
   Label fallthrough;
   __ ld(a0, register_location(start_reg));  // Index of start of capture.
   __ ld(a1, register_location(start_reg + 1));  // Index of end of capture.
   __ Dsubu(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) {
-    __ ld(t1, MemOperand(frame_pointer(), kStringStartMinusOne));
-    __ Daddu(t1, t1, a1);
-    BranchOrBacktrack(on_no_match, le, current_input_offset(), Operand(t1));
-  } else {
-    __ Daddu(t1, a1, current_input_offset());
-    // Check that there are enough characters left in the input.
-    BranchOrBacktrack(on_no_match, gt, t1, Operand(zero_reg));
-  }
+  __ Daddu(t1, a1, current_input_offset());
+  // Check that there are enough characters left in the input.
+  BranchOrBacktrack(on_no_match, gt, t1, Operand(zero_reg));
 
   if (mode_ == LATIN1) {
     Label success;
@@ -280,9 +283,6 @@
     // a1 - length of capture.
     __ Daddu(a0, a0, Operand(end_of_input_address()));
     __ Daddu(a2, end_of_input_address(), Operand(current_input_offset()));
-    if (read_backward) {
-      __ Dsubu(a2, a2, Operand(a1));
-    }
     __ Daddu(a1, a0, Operand(a1));
 
     // a0 - Address of start of capture.
@@ -321,12 +321,6 @@
     __ bind(&success);
     // Compute new value of character position after the matched part.
     __ Dsubu(current_input_offset(), a2, end_of_input_address());
-    if (read_backward) {
-      __ ld(t1, register_location(start_reg));  // Index of start of capture.
-      __ ld(a2, register_location(start_reg + 1));  // Index of end of capture.
-      __ Daddu(current_input_offset(), current_input_offset(), Operand(t1));
-      __ Dsubu(current_input_offset(), current_input_offset(), Operand(a2));
-    }
   } else {
     DCHECK(mode_ == UC16);
     // Put regexp engine registers on stack.
@@ -355,9 +349,6 @@
     __ mov(s3, a1);
     // Address of current input position.
     __ Daddu(a1, current_input_offset(), Operand(end_of_input_address()));
-    if (read_backward) {
-      __ Dsubu(a1, a1, Operand(s3));
-    }
     // Isolate.
     __ li(a3, Operand(ExternalReference::isolate_address(masm_->isolate())));
 
@@ -376,20 +367,16 @@
     // Check if function returned non-zero for success or zero for failure.
     BranchOrBacktrack(on_no_match, eq, v0, Operand(zero_reg));
     // On success, increment position by length of capture.
-    if (read_backward) {
-      __ Dsubu(current_input_offset(), current_input_offset(), Operand(s3));
-    } else {
-      __ Daddu(current_input_offset(), current_input_offset(), Operand(s3));
-    }
+    __ Daddu(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;
 
@@ -397,28 +384,16 @@
   __ ld(a0, register_location(start_reg));
   __ ld(a1, register_location(start_reg + 1));
   __ Dsubu(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.
+  // Succeed on empty capture (including no capture).
   __ Branch(&fallthrough, eq, a1, Operand(zero_reg));
 
-  if (read_backward) {
-    __ ld(t1, MemOperand(frame_pointer(), kStringStartMinusOne));
-    __ Daddu(t1, t1, a1);
-    BranchOrBacktrack(on_no_match, le, current_input_offset(), Operand(t1));
-  } else {
-    __ Daddu(t1, a1, current_input_offset());
-    // Check that there are enough characters left in the input.
-    BranchOrBacktrack(on_no_match, gt, t1, Operand(zero_reg));
-  }
+  __ Daddu(t1, a1, current_input_offset());
+  // Check that there are enough characters left in the input.
+  BranchOrBacktrack(on_no_match, gt, t1, Operand(zero_reg));
 
   // Compute pointers to match string and capture string.
   __ Daddu(a0, a0, Operand(end_of_input_address()));
   __ Daddu(a2, end_of_input_address(), Operand(current_input_offset()));
-  if (read_backward) {
-    __ Dsubu(a2, a2, Operand(a1));
-  }
   __ Daddu(a1, a1, Operand(a0));
 
   Label loop;
@@ -440,12 +415,6 @@
 
   // Move current character position to position after match.
   __ Dsubu(current_input_offset(), a2, end_of_input_address());
-  if (read_backward) {
-    __ ld(t1, register_location(start_reg));      // Index of start of capture.
-    __ ld(a2, register_location(start_reg + 1));  // Index of end of capture.
-    __ Daddu(current_input_offset(), current_input_offset(), Operand(t1));
-    __ Dsubu(current_input_offset(), current_input_offset(), Operand(a2));
-  }
   __ bind(&fallthrough);
 }
 
@@ -675,7 +644,7 @@
     __ Daddu(frame_pointer(), sp, Operand(8 * 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;
@@ -718,7 +687,7 @@
     __ Dsubu(a0, a0, t1);
     // Store this value in a local variable, for use when clearing
     // position registers.
-    __ sd(a0, MemOperand(frame_pointer(), kStringStartMinusOne));
+    __ sd(a0, MemOperand(frame_pointer(), kInputStartMinusOne));
 
     // Initialize code pointer register
     __ li(code_pointer(), Operand(masm_->CodeObject()), CONSTANT_SIZE);
@@ -828,7 +797,7 @@
         __ sd(a2, MemOperand(frame_pointer(), kRegisterOutput));
 
         // Prepare a0 to initialize registers with its value in the next run.
-        __ ld(a0, MemOperand(frame_pointer(), kStringStartMinusOne));
+        __ ld(a0, MemOperand(frame_pointer(), kInputStartMinusOne));
 
         if (global_with_zero_length_check()) {
           // Special case for zero-length matches.
@@ -982,13 +951,10 @@
                                                     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);
 }
@@ -1096,7 +1062,7 @@
 
 void RegExpMacroAssemblerMIPS::ClearRegisters(int reg_from, int reg_to) {
   DCHECK(reg_from <= reg_to);
-  __ ld(a0, MemOperand(frame_pointer(), kStringStartMinusOne));
+  __ ld(a0, MemOperand(frame_pointer(), kInputStartMinusOne));
   for (int reg = reg_from; reg <= reg_to; reg++) {
     __ sd(a0, register_location(reg));
   }
@@ -1209,14 +1175,10 @@
 
 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 {
-    __ ld(a1, MemOperand(frame_pointer(), kStringStartMinusOne));
-    __ Daddu(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()));
 }