Pull in r257902 from upstream llvm trunk, by James Y Knight (this will

be merged to the official release_38 branch soon, but we need it ASAP):

  Stop increasing alignment of externally-visible globals on ELF
  platforms.

  With ELF, the alignment of a global variable in a shared library will
  get copied into an executables linked against it, if the executable even
  accesss the variable. So, it's not possible to implicitly increase
  alignment based on access patterns, or you'll break existing binaries.

  This happened to affect libc++'s std::cout symbol, for example. See
  thread: http://thread.gmane.org/gmane.comp.compilers.clang.devel/45311

  (This is a re-commit of r257719, without the bug reported in
  PR26144. I've tweaked the code to not assert-fail in
  enforceKnownAlignment when computeKnownBits doesn't recurse far enough
  to find the underlying Alloca/GlobalObject value.)

  Differential Revision: http://reviews.llvm.org/D16145

1 files changed, 2 insertions, 2 deletions

diff --git a/contrib/llvm/lib/CodeGen/CodeGenPrepare.cpp b/contrib/llvm/lib/CodeGen/CodeGenPrepare.cpp
index 03e5778..fd4ee46 100644
--- a/contrib/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/contrib/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -1742,8 +1742,8 @@ bool CodeGenPrepare::optimizeCallInst(CallInst *CI, bool& ModifiedDT) {
       // over-aligning global variables that have an explicit section is
       // forbidden.
       GlobalVariable *GV;
-      if ((GV = dyn_cast<GlobalVariable>(Val)) && GV->hasUniqueInitializer() &&
-          !GV->hasSection() && GV->getAlignment() < PrefAlign &&
+      if ((GV = dyn_cast<GlobalVariable>(Val)) && GV->canIncreaseAlignment() &&
+          GV->getAlignment() < PrefAlign &&
           DL->getTypeAllocSize(GV->getType()->getElementType()) >=
               MinSize + Offset2)
         GV->setAlignment(PrefAlign);