svn commit: r289072 - in head/contrib: libc++/src llvm/lib/Transforms/Vectorize

[Dimitry Andric]

Author: dim
Date: Fri Oct  9 18:21:45 2015
New Revision: 289072
URL: https://svnweb.freebsd.org/changeset/base/289072

Log:
  Temporarily revert upstream llvm trunk r240144 (by Michael Zolotukhin):
  
    [SLP] Vectorize for all-constant entries.
  
  This should fix libc++'s iostream initialization SIGBUSing on amd64,
  whenever the global cout symbol is not aligned to 16 bytes.
  
  Some further explanation: libc++'s iostream.cpp contains the definitions
  of std::cout, std::cerr and so on.  These global objects are effectively
  declared with an alignment of 8 bytes.  When an executable is linked
  against libc++.so, it can sometimes get a copy of the global object,
  which is then at the same alignment.
  
  However, with clang 3.7.0, the initialization of these global objects
  will incorrectly use SSE instructions (e.g. movdqa), whenever the
  optimization level is high enough, and SSE is enabled, such as on amd64.
  When any of these objects is not aligned to 16 bytes, this will result
  in a SIGBUS during iostream initialization.  In contrast, clang 3.6.x
  and earlier took the 8 byte alignment into consideration, and avoided
  SSE for those particular operations.
  
  After bisecting of upstream changes, I found that the above revision
  caused the change of this behavior, so I am reverting it now as a
  workaround, while a discussion and test case is being prepared for
  upstream.

Modified:
  head/contrib/libc++/src/iostream.cpp
  head/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

Modified: head/contrib/libc++/src/iostream.cpp
==============================================================================
--- head/contrib/libc++/src/iostream.cpp	Fri Oct  9 17:46:05 2015	(r289071)
+++ head/contrib/libc++/src/iostream.cpp	Fri Oct  9 18:21:45 2015	(r289072)
@@ -86,3 +86,4 @@ ios_base::Init::~Init()
 }
 
 _LIBCPP_END_NAMESPACE_STD
+

Modified: head/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
==============================================================================
--- head/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp	Fri Oct  9 17:46:05 2015	(r289071)
+++ head/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp	Fri Oct  9 18:21:45 2015	(r289072)
@@ -1642,10 +1642,8 @@ bool BoUpSLP::isFullyVectorizableTinyTre
   if (VectorizableTree.size() != 2)
     return false;
 
-  // Handle splat and all-constants stores.
-  if (!VectorizableTree[0].NeedToGather &&
-      (allConstant(VectorizableTree[1].Scalars) ||
-       isSplat(VectorizableTree[1].Scalars)))
+  // Handle splat stores.
+  if (!VectorizableTree[0].NeedToGather && isSplat(VectorizableTree[1].Scalars))
     return true;
 
   // Gathering cost would be too much for tiny trees.