Implement target independent TLS compatible with glibc's emutls.c.

The 'common' section TLS is not implemented.
Current C/C++ TLS variables are not placed in common section.
DWARF debug info to get the address of TLS variables is not generated yet.

clang and driver changes in http://reviews.llvm.org/D10524

  Added -femulated-tls flag to select the emulated TLS model,
  which will be used for old targets like Android that do not
  support ELF TLS models.

Added TargetLowering::LowerToTLSEmulatedModel as a target-independent
function to convert a SDNode of TLS variable address to a function call
to __emutls_get_address.

Added into lib/Target/*/*ISelLowering.cpp to call LowerToTLSEmulatedModel
for TLSModel::Emulated. Although all targets supporting ELF TLS models are
enhanced, emulated TLS model has been tested only for Android ELF targets.
Modified AsmPrinter.cpp to print the emutls_v.* and emutls_t.* variables for
emulated TLS variables.
Modified DwarfCompileUnit.cpp to skip some DIE for emulated TLS variabls.

TODO: Add proper DIE for emulated TLS variables.
      Added new unit tests with emulated TLS.

Differential Revision: http://reviews.llvm.org/D10522

llvm-svn: 243438
diff --git a/llvm/test/CodeGen/X86/tls-android.ll b/llvm/test/CodeGen/X86/tls-android.ll
new file mode 100644
index 0000000..4156c7b
--- /dev/null
+++ b/llvm/test/CodeGen/X86/tls-android.ll
@@ -0,0 +1,89 @@
+; RUN: llc < %s -emulated-tls -march=x86 -mtriple=x86_64-linux-android -relocation-model=pic | FileCheck  %s
+; RUN: llc < %s -emulated-tls -march=x86-64 -mtriple=x86_64-linux-android -relocation-model=pic | FileCheck -check-prefix=X64 %s
+
+; Make sure that TLS symboles are emitted in expected order.
+
+@external_x = external thread_local global i32
+@external_y = thread_local global i32 7
+@internal_y = internal thread_local global i32 9
+
+define i32* @get_external_x() {
+entry:
+  ret i32* @external_x
+}
+
+define i32* @get_external_y() {
+entry:
+  ret i32* @external_y
+}
+
+define i32* @get_internal_y() {
+entry:
+  ret i32* @internal_y
+}
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; 32-bit mode
+; CHECK-LABEL: get_external_x:
+; CHECK:  __emutls_v.external_x
+; CHECK:  __emutls_get_address
+
+; CHECK-LABEL: get_external_y:
+; CHECK:  __emutls_v.external_y
+; CHECK:  __emutls_get_address
+
+; CHECK-LABEL: get_internal_y:
+; CHECK:  __emutls_v.internal_y
+; CHECK:  __emutls_get_address
+
+; CHECK-NOT: __emutls_v.external_x:
+
+; CHECK:       .align 4
+; CHECK-LABEL: __emutls_v.external_y:
+; CHECK-NEXT:  .long 4
+; CHECK-NEXT:  .long 4
+; CHECK-NEXT:  .long 0
+; CHECK-NEXT:  .long __emutls_t.external_y
+; CHECK-LABEL: __emutls_t.external_y:
+; CHECK-NEXT:  .long 7
+
+; CHECK:       .align 4
+; CHECK-LABEL: __emutls_v.internal_y:
+; CHECK-NEXT:  .long 4
+; CHECK-NEXT:  .long 4
+; CHECK-NEXT:  .long 0
+; CHECK-NEXT:  .long __emutls_t.internal_y
+; CHECK-LABEL: __emutls_t.internal_y:
+; CHECK-NEXT:  .long 9
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; 64-bit mode
+; X64-LABEL: get_external_x:
+; X64:  __emutls_v.external_x
+; X64:  __emutls_get_address
+
+; X64-LABEL: get_external_y:
+; X64:  __emutls_v.external_y
+; X64:  __emutls_get_address
+
+; X64-LABEL: get_internal_y:
+; X64:  __emutls_v.internal_y
+; X64:  __emutls_get_address
+
+; X64-NOT: __emutls_v.external_x:
+
+; X64:       .align 8
+; X64-LABEL: __emutls_v.external_y:
+; X64-NEXT:  .quad 4
+; X64-NEXT:  .quad 4
+; X64-NEXT:  .quad 0
+; X64-NEXT:  .quad __emutls_t.external_y
+; X64-LABEL: __emutls_t.external_y:
+; X64-NEXT:  .long 7
+
+; X64:       .align 8
+; X64-LABEL: __emutls_v.internal_y:
+; X64-NEXT:  .quad 4
+; X64-NEXT:  .quad 4
+; X64-NEXT:  .quad 0
+; X64-NEXT:  .quad __emutls_t.internal_y
+; X64-LABEL: __emutls_t.internal_y:
+; X64-NEXT:  .long 9