Cache contains only ascii in StringImpl

third_party/WebKit/Source/wtf/text/StringImpl.h

Index: third_party/WebKit/Source/wtf/text/StringImpl.h
diff --git a/third_party/WebKit/Source/wtf/text/StringImpl.h b/third_party/WebKit/Source/wtf/text/StringImpl.h
index 680b40ab284190f3b24656cf8461501b6548bd23..8e2b18f7b3d60981cf418c151e580532f49f607f 100644
--- a/third_party/WebKit/Source/wtf/text/StringImpl.h
+++ b/third_party/WebKit/Source/wtf/text/StringImpl.h
@@ -30,6 +30,7 @@
 #include "wtf/StringHasher.h"
 #include "wtf/Vector.h"
 #include "wtf/WTFExport.h"
+#include "wtf/text/ASCIIFastPath.h"
 #include "wtf/text/Unicode.h"
 #include <limits.h>
 #include <string.h>
@@ -133,6 +134,8 @@ class WTF_EXPORT StringImpl {
       : m_refCount(1),
         m_length(0),
         m_hash(0),
+        m_containsOnlyASCII(false),

[esprehn, 2017/01/04 20:30:37]

true

[Charlie Harrison, 2017/01/04 20:53:51]

Done.

+        m_needsASCIICheck(true),

[esprehn, 2017/01/04 20:30:37]

false

[Charlie Harrison, 2017/01/04 20:53:51]

Done.

         m_isAtomic(false),
         m_is8Bit(true),
         m_isStatic(true) {
@@ -149,6 +152,8 @@ class WTF_EXPORT StringImpl {
       : m_refCount(1),
         m_length(0),
         m_hash(0),
+        m_containsOnlyASCII(false),

[esprehn, 2017/01/04 20:30:37]

m_containsOnlyASCII(true), the string is empty

[Charlie Harrison, 2017/01/04 20:53:51]

Done.

+        m_needsASCIICheck(true),

[esprehn, 2017/01/04 20:30:37]

false

[Charlie Harrison, 2017/01/04 20:53:50]

Done.

         m_isAtomic(false),
         m_is8Bit(false),
         m_isStatic(true) {
@@ -162,6 +167,8 @@ class WTF_EXPORT StringImpl {
       : m_refCount(1),
         m_length(length),
         m_hash(0),
+        m_containsOnlyASCII(false),

[esprehn, 2017/01/04 20:30:37]

(!length)

[Charlie Harrison, 2017/01/04 20:53:51]

Done.

+        m_needsASCIICheck(true),

[esprehn, 2017/01/04 20:30:37]

(length)

[Charlie Harrison, 2017/01/04 20:53:50]

Done.

         m_isAtomic(false),
         m_is8Bit(true),
         m_isStatic(false) {
@@ -173,6 +180,8 @@ class WTF_EXPORT StringImpl {
       : m_refCount(1),
         m_length(length),
         m_hash(0),
+        m_containsOnlyASCII(false),

[esprehn, 2017/01/04 20:30:37]

(!length)

[Charlie Harrison, 2017/01/04 20:53:50]

Done.

+        m_needsASCIICheck(true),

[esprehn, 2017/01/04 20:30:37]

(length)

[Charlie Harrison, 2017/01/04 20:53:50]

Done.

         m_isAtomic(false),
         m_is8Bit(false),
         m_isStatic(false) {
@@ -185,6 +194,8 @@ class WTF_EXPORT StringImpl {
       : m_refCount(1),
         m_length(length),
         m_hash(hash),
+        m_containsOnlyASCII(false),
+        m_needsASCIICheck(true),

[esprehn, 2017/01/04 20:30:37]

ditto

[Charlie Harrison, 2017/01/04 20:53:50]

Done.

         m_isAtomic(false),
         m_is8Bit(true),
         m_isStatic(true) {}
@@ -253,6 +264,8 @@ class WTF_EXPORT StringImpl {
 
   bool isStatic() const { return m_isStatic; }
 
+  bool containsOnlyASCII() const;
+
   bool isSafeToSendToAnotherThread() const;
 
   // The high bits of 'hash' are always empty, but we prefer to store our
@@ -494,6 +507,8 @@ class WTF_EXPORT StringImpl {
   unsigned m_refCount;
   const unsigned m_length;
   mutable unsigned m_hash : 24;
+  mutable unsigned m_containsOnlyASCII : 1;
+  mutable unsigned m_needsASCIICheck : 1;
   unsigned m_isAtomic : 1;
   const unsigned m_is8Bit : 1;
   const unsigned m_isStatic : 1;
@@ -527,6 +542,17 @@ inline bool equal(const char* a, StringImpl* b) {
 }
 WTF_EXPORT bool equalNonNull(const StringImpl* a, const StringImpl* b);
 
+ALWAYS_INLINE bool StringImpl::containsOnlyASCII() const {
+  if (m_needsASCIICheck) {
+    m_containsOnlyASCII =
+        !length() ||

[esprehn, 2017/01/04 20:30:37]

Strings are immutable, so you don't need the length check here, you can do it in
the constructor.

[Charlie Harrison, 2017/01/04 20:53:50]

Done.

+        (is8Bit() ? charactersAreAllASCII(characters8(), length())
+                  : charactersAreAllASCII(characters16(), length()));

[esprehn, 2017/01/04 20:30:37]

This is inlining a lot of code which I know the old code did, but  instead I
think you want to put the slow path in a separate out of line method, and only
ALWAYS_INLINE the fast path. That'll actually be faster since it makes the
functions smaller.

ALWAYS_INLINE bool StringImpl::containsOnlyASCII() const {
  if (m_needsASCIICheck)
    updateContainsOnlyASCII();
  return m_containsOnlyASCII;
}

and updateContainsOnlyASCII is in the .cpp file out of line.

[Charlie Harrison, 2017/01/04 20:53:50]

SGTM. Done.

+    m_needsASCIICheck = false;
+  }
+  return m_containsOnlyASCII;
+}
+
 template <typename CharType>
 ALWAYS_INLINE bool equal(const CharType* a,
                          const CharType* b,