From d361766d4bea0599f15d2da2a4fe62dd87e4d882 Mon Sep 17 00:00:00 2001 From: Dimitry Andric Date: Fri, 9 Oct 2015 18:21:45 +0000 Subject: [PATCH] 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. --- contrib/libc++/src/iostream.cpp | 1 + contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp | 6 ++---- 2 files changed, 3 insertions(+), 4 deletions(-) diff --git a/contrib/libc++/src/iostream.cpp b/contrib/libc++/src/iostream.cpp index e073aec6ead5..9a82e27a497f 100644 --- a/contrib/libc++/src/iostream.cpp +++ b/contrib/libc++/src/iostream.cpp @@ -86,3 +86,4 @@ ios_base::Init::~Init() } _LIBCPP_END_NAMESPACE_STD + diff --git a/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp index 7bac407e77e9..b180c976c233 100644 --- a/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp +++ b/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp @@ -1642,10 +1642,8 @@ bool BoUpSLP::isFullyVectorizableTinyTree() { 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.