Implement the local-dynamic TLS model for x86 (PR3985)

This implements codegen support for accesses to thread-local variables
using the local-dynamic model, and adds a clean-up pass so that the base
address for the TLS block can be re-used between local-dynamic access on
an execution path.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157818 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/X86/X86TargetMachine.cpp

@@ -147,6 +147,10 @@ bool X86PassConfig::addInstSelector() {
   // Install an instruction selector.
   PM->add(createX86ISelDag(getX86TargetMachine(), getOptLevel()));
 
+  // For ELF, cleanup any local-dynamic TLS accesses.
+  if (getX86Subtarget().isTargetELF() && getOptLevel() != CodeGenOpt::None)
+    PM->add(createCleanupLocalDynamicTLSPass());
+
   // For 32-bit, prepend instructions to set the "global base reg" for PIC.
   if (!getX86Subtarget().is64Bit())
     PM->add(createGlobalBaseRegPass());