[optimizing] Address x86_64 RIP patch comments

Nicolas had some comments after the patch
https://android-review.googlesource.com/#/c/144100 had merged.  Fix the
problems that he found.

Change-Id: I40e8a4273997860db7511dc8f1986281b72bead2
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>

2 files changed, 26 insertions, 51 deletions

diff --git a/compiler/utils/x86_64/assembler_x86_64.cc b/compiler/utils/x86_64/assembler_x86_64.cc
index cb6d400618..638659d635 100644
--- a/compiler/utils/x86_64/assembler_x86_64.cc
+++ b/compiler/utils/x86_64/assembler_x86_64.cc
@@ -2742,14 +2742,14 @@ void X86_64ExceptionSlowPath::Emit(Assembler *sasm) {
 
 void X86_64Assembler::AddConstantArea() {
   const std::vector<int32_t>& area = constant_area_.GetBuffer();
-  for (size_t i = 0, u = area.size(); i < u; i++) {
+  for (size_t i = 0, e = area.size(); i < e; i++) {
     AssemblerBuffer::EnsureCapacity ensured(&buffer_);
     EmitInt32(area[i]);
   }
 }
 
 int ConstantArea::AddInt32(int32_t v) {
-  for (size_t i = 0, u = buffer_.size(); i < u; i++) {
+  for (size_t i = 0, e = buffer_.size(); i < e; i++) {
     if (v == buffer_[i]) {
       return i * elem_size_;
     }
@@ -2766,8 +2766,8 @@ int ConstantArea::AddInt64(int64_t v) {
   int32_t v_high = v >> 32;
   if (buffer_.size() > 1) {
     // Ensure we don't pass the end of the buffer.
-    for (size_t i = 0, u = buffer_.size() - 1; i < u; i++) {
-      if (v_low == buffer_[i] && v_high == buffer_[i+1]) {
+    for (size_t i = 0, e = buffer_.size() - 1; i < e; i++) {
+      if (v_low == buffer_[i] && v_high == buffer_[i + 1]) {
         return i * elem_size_;
       }
     }
diff --git a/compiler/utils/x86_64/assembler_x86_64.h b/compiler/utils/x86_64/assembler_x86_64.h
index ef6205c870..15b8b15c74 100644
--- a/compiler/utils/x86_64/assembler_x86_64.h
+++ b/compiler/utils/x86_64/assembler_x86_64.h
@@ -235,6 +235,8 @@ class Address : public Operand {
       result.SetSIB(TIMES_1, CpuRegister(RSP), CpuRegister(RBP));
       result.SetDisp32(addr);
     } else {
+      // RIP addressing is done using RBP as the base register.
+      // The value in RBP isn't used.  Instead the offset is added to RIP.
       result.SetModRM(0, CpuRegister(RBP));
       result.SetDisp32(addr);
     }
@@ -244,6 +246,8 @@ class Address : public Operand {
   // An RIP relative address that will be fixed up later.
   static Address RIP(AssemblerFixup* fixup) {
     Address result;
+    // RIP addressing is done using RBP as the base register.
+    // The value in RBP isn't used.  Instead the offset is added to RIP.
     result.SetModRM(0, CpuRegister(RBP));
     result.SetDisp32(0);
     result.SetFixup(fixup);
@@ -267,32 +271,20 @@ class ConstantArea {
   public:
     ConstantArea() {}
 
-    /**
-     * Add a double to the constant area.
-     * @param v literal to be added to the constant area.
-     * @returns the offset in the constant area where the literal resides.
-     */
+    // Add a double to the constant area, returning the offset into
+    // the constant area where the literal resides.
     int AddDouble(double v);
 
-    /**
-     * Add a float to the constant area.
-     * @param v literal to be added to the constant area.
-     * @returns the offset in the constant area where the literal resides.
-     */
+    // Add a float to the constant area, returning the offset into
+    // the constant area where the literal resides.
     int AddFloat(float v);
 
-    /**
-     * Add an int32_t to the constant area.
-     * @param v literal to be added to the constant area.
-     * @returns the offset in the constant area where the literal resides.
-     */
+    // Add an int32_t to the constant area, returning the offset into
+    // the constant area where the literal resides.
     int AddInt32(int32_t v);
 
-    /**
-     * Add an int64_t to the constant area.
-     * @param v literal to be added to the constant area.
-     * @returns the offset in the constant area where the literal resides.
-     */
+    // Add an int64_t to the constant area, returning the offset into
+    // the constant area where the literal resides.
     int AddInt64(int64_t v);
 
     int GetSize() const {
@@ -736,43 +728,26 @@ class X86_64Assembler FINAL : public Assembler {
   // and branch to a ExceptionSlowPath if it is.
   void ExceptionPoll(ManagedRegister scratch, size_t stack_adjust) OVERRIDE;
 
-  /**
-   * Add a double to the constant area.
-   * @param v literal to be added to the constant area.
-   * @returns the offset in the constant area where the literal resides.
-   */
+  // Add a double to the constant area, returning the offset into
+  // the constant area where the literal resides.
   int AddDouble(double v) { return constant_area_.AddDouble(v); }
 
-  /**
-   * Add a float to the constant area.
-   * @param v literal to be added to the constant area.
-   * @returns the offset in the constant area where the literal resides.
-   */
+  // Add a float to the constant area, returning the offset into
+  // the constant area where the literal resides.
   int AddFloat(float v)   { return constant_area_.AddFloat(v); }
 
-  /**
-   * Add an int32_t to the constant area.
-   * @param v literal to be added to the constant area.
-   * @returns the offset in the constant area where the literal resides.
-   */
+  // Add an int32_t to the constant area, returning the offset into
+  // the constant area where the literal resides.
   int AddInt32(int32_t v) { return constant_area_.AddInt32(v); }
 
-  /**
-   * Add an int64_t to the constant area.
-   * @param v literal to be added to the constant area.
-   * @returns the offset in the constant area where the literal resides.
-   */
+  // Add an int64_t to the constant area, returning the offset into
+  // the constant area where the literal resides.
   int AddInt64(int64_t v) { return constant_area_.AddInt64(v); }
 
-  /**
-   * Add the contents of the constant area to the assembler buffer.
-   */
+  // Add the contents of the constant area to the assembler buffer.
   void AddConstantArea();
 
-  /**
-   * Is the constant area empty?
-   * @returns 'true' if there are no literals in the constant area.
-   */
+  // Is the constant area empty? Return true if there are no literals in the constant area.
   bool IsConstantAreaEmpty() const { return constant_area_.GetSize() == 0; }
 
  private: