Work around a MSVC 2012 Update 1 bug causing a crash on x86

https://bugs.webkit.org/show_bug.cgi?id=110488

Reviewed by Anders Carlsson.

The crash happens when building with /O2, where TextEncodingNameHash::equal is
incorrectly optimized with the inlined toASCIILower and uses a register already in use.
The function returns false incorrectly, causing a mismatch of text encoding name which
then results in a null pointer access.

Slightly rewording the use of the inline function lets the compiler produce correct code.

The bug has already been reported and should be fixed in the next release of MSVS later this year.
https://connect.microsoft.com/VisualStudio/feedback/details/777533/vs2012-c-optimizing-bug-when-using-inline-and-char-return-type-x86-target-only

* platform/text/TextEncodingRegistry.cpp:

Task-number: QTBUG-29719
Change-Id: I9fda5528ba3aefcd7c6b6c1042cf3ceb5e325b06
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144042 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/Source/WebCore/platform/text/TextEncodingRegistry.cpp b/Source/WebCore/platform/text/TextEncodingRegistry.cpp
index 2790227fa..6e95a44fe 100644
--- a/Source/WebCore/platform/text/TextEncodingRegistry.cpp
+++ b/Source/WebCore/platform/text/TextEncodingRegistry.cpp
@@ -71,10 +71,19 @@ struct TextEncodingNameHash {
         char c1;
         char c2;
         do {
+#if defined(_MSC_FULL_VER) && _MSC_FULL_VER == 170051106
+            // Workaround for a bug in the VS2012 Update 1 optimizer, remove once the fix is released.
+            // https://connect.microsoft.com/VisualStudio/feedback/details/777533/vs2012-c-optimizing-bug-when-using-inline-and-char-return-type-x86-target-only
+            c1 = toASCIILower(*s1++);
+            c2 = toASCIILower(*s2++);
+            if (c1 != c2)
+                return false;
+#else
             c1 = *s1++;
             c2 = *s2++;
             if (toASCIILower(c1) != toASCIILower(c2))
                 return false;
+#endif
         } while (c1 && c2);
         return !c1 && !c2;
     }