[arm64] Generate adds/ands.

src/compiler/instruction-selector.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_INSTRUCTION_SELECTOR_H_
 #define V8_COMPILER_INSTRUCTION_SELECTOR_H_
 
 #include <map>
 
 #include "src/compiler/common-operator.h"
@@ skipping 133 matching lines @@
   // ===========================================================================
   // ============ Architecture-independent graph covering methods. =============
   // ===========================================================================
 
   // Used in pattern matching during code generation.
   // Check if {node} can be covered while generating code for the current
   // instruction. A node can be covered if the {user} of the node has the only
   // edge and the two are in the same basic block.
   bool CanCover(Node* user, Node* node) const;
 
+  // Used in pattern matching during code generation.
+  // This function checks that {node} and {user} are in the same basic block,
+  // and that {user} is the only user of {node} in this basic block.  This
+  // check guarantees that there are no users of {node} scheduled between
+  // {node} and {user}, and thus we can select a single instruction for both
+  // nodes, if such an instruction exists. This check can be used for example
+  // when selecting instructions for:
+  //   n = Int32Add(a, b)
+  //   c = Word32Compare(n, 0, cond)
+  //   Branch(c, true_label, false_label)
+  // Here we can generate a flag-setting add instruction, even if the add has
+  // uses in other basic blocks, since the flag-setting add instruction will
+  // still generate the result of the addition and not just set the flags.
+  // However, if we had uses of the add in the same basic block, we could have:
+  //   n = Int32Add(a, b)
+  //   o = OtherOp(n, ...)
+  //   c = Word32Compare(n, 0, cond)
+  //   Branch(c, true_label, false_label)
+  // where we cannot select the add and the compare together.  If we were to
+  // select a flag-setting add instruction for Word32Compare and Int32Add while
+  // visiting Word32Compare, we would then have to select an instruction for
+  // OtherOp *afterwards*, which means we would attempt to use the result of
+  // the add before we have defined it.
+  bool IsOnlyUserOfNodeInSameBlock(Node* user, Node* node) const;
+
   // Checks if {node} was already defined, and therefore code was already
   // generated for it.
   bool IsDefined(Node* node) const;
 
   // Checks if {node} has any uses, and therefore code has to be generated for
   // it.
   bool IsUsed(Node* node) const;
 
   // Checks if {node} is currently live.
   bool IsLive(Node* node) const { return !IsDefined(node) && IsUsed(node); }
@@ skipping 137 matching lines @@
   IntVector virtual_registers_;
   InstructionScheduler* scheduler_;
   Frame* frame_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_SELECTOR_H_