TLS support for MinGW targets.

[klickverbot]

Summary

MinGW is almost completely compatible to MSVC, with the exception of the _tls_array global not being available.

[asl]

LGTM

[asl]

r177257

lib/Target/X86/X86ISelLowering.cpp

if (Subtarget->isTargetDarwin()) {
 
     // And our return value (tls address) is in the standard call return value
     // location.
     unsigned Reg = Subtarget->is64Bit() ? X86::RAX : X86::EAX;
     return DAG.getCopyFromReg(Chain, DL, Reg, getPointerTy(),
                               Chain.getValue(1));
   }
 
-  if (Subtarget->isTargetWindows()) {
+  if (Subtarget->isTargetWindows() || Subtarget->isTargetMingw()) {
     // Just use the implicit TLS architecture
     // Need to generate someting similar to:
     //   mov     rdx, qword [gs:abs 58H]; Load pointer to ThreadLocalStorage
     //                                  ; from TEB
     //   mov     ecx, dword [rel _tls_index]: Load index (from C runtime)
     //   mov     rcx, qword [rdx+rcx*8]
     //   mov     eax, .tls$:tlsvar
     //   [rax+rcx] contains the address
     // Windows 64bit: gs:0x58
     // Windows 32bit: fs:__tls_array
 
     // If GV is an alias then use the aliasee for determining
     // thread-localness.
     if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(GV))
       GV = GA->resolveAliasedGlobal(false);
     DebugLoc dl = GA->getDebugLoc();
     SDValue Chain = DAG.getEntryNode();
 
     // Get the Thread Pointer, which is %fs:__tls_array (32-bit) or
-    // %gs:0x58 (64-bit).
+    // %gs:0x58 (64-bit). On MinGW, __tls_array is not available, so directly
+    // use its literal value of 0x2C.
     Value *Ptr = Constant::getNullValue(Subtarget->is64Bit()
                                         ? Type::getInt8PtrTy(*DAG.getContext(),
                                                              256)
                                         : Type::getInt32PtrTy(*DAG.getContext(),
                                                               257));
 
-    SDValue ThreadPointer = DAG.getLoad(getPointerTy(), dl, Chain,
-                                        Subtarget->is64Bit()
-                                        ? DAG.getIntPtrConstant(0x58)
-                                        : DAG.getExternalSymbol("_tls_array",
-                                                                getPointerTy()),
+    SDValue TlsArray = Subtarget->is64Bit() ? DAG.getIntPtrConstant(0x58) :
+      (Subtarget->isTargetMingw() ? DAG.getIntPtrConstant(0x2C) :
+        DAG.getExternalSymbol("_tls_array", getPointerTy()));
+
+    SDValue ThreadPointer = DAG.getLoad(getPointerTy(), dl, Chain, TlsArray,
                                         MachinePointerInfo(Ptr),
                                         false, false, false, 0);
 
     // Load the _tls_index variable
     SDValue IDX = DAG.getExternalSymbol("_tls_index", getPointerTy());
     if (Subtarget->is64Bit())
       IDX = DAG.getExtLoad(ISD::ZEXTLOAD, dl, getPointerTy(), Chain,
                            IDX, MachinePointerInfo(), MVT::i32,