Reapply: [mips] Handle MipsMCExpr sub-expression for the MEK_DTPREL tag

This reapplies commit r351987 with a failed test fix. Now the test
accepts both DW_OP_GNU_push_tls_address and DW_OP_form_tls_address
opcode.

Original commit message:
```
  This is a fix for a regression introduced by the rL348194 commit. In
  that change new type (MEK_DTPREL) of MipsMCExpr expression was added,
  but in some places of the code this type of expression considered as
  unexpected.

  This change fixes the bug. The MEK_DTPREL type of expression is used for
  marking TLS DIEExpr only and contains a regular sub-expression. Where we
  need to handle the expression, we retrieve the sub-expression and
  handle it in a common way.
```

llvm-svn: 352034

2 files changed, 11 insertions, 8 deletions

diff --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp b/llvm/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp
index 32931c033e5..3d3003a0811 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp
@@ -613,8 +613,9 @@ getExprOpValue(const MCExpr *Expr, SmallVectorImpl<MCFixup> &Fixups,
       llvm_unreachable("Unhandled fixup kind!");
       break;
     case MipsMCExpr::MEK_DTPREL:
-      llvm_unreachable("MEK_DTPREL is used for TLS DIEExpr only");
-      break;
+      // MEK_DTPREL is used for marking TLS DIEExpr only
+      // and contains a regular sub-expression.
+      return getExprOpValue(MipsExpr->getSubExpr(), Fixups, STI);
     case MipsMCExpr::MEK_CALL_HI16:
       FixupKind = Mips::fixup_Mips_CALL_HI16;
       break;
diff --git a/llvm/lib/Target/Mips/MCTargetDesc/MipsMCExpr.cpp b/llvm/lib/Target/Mips/MCTargetDesc/MipsMCExpr.cpp
index 42bc847bb61..680806c4deb 100644
--- a/llvm/lib/Target/Mips/MCTargetDesc/MipsMCExpr.cpp
+++ b/llvm/lib/Target/Mips/MCTargetDesc/MipsMCExpr.cpp
@@ -43,8 +43,10 @@ void MipsMCExpr::printImpl(raw_ostream &OS, const MCAsmInfo *MAI) const {
     llvm_unreachable("MEK_None and MEK_Special are invalid");
     break;
   case MEK_DTPREL:
-    llvm_unreachable("MEK_DTPREL is used for TLS DIEExpr only");
-    break;
+    // MEK_DTPREL is used for marking TLS DIEExpr only
+    // and contains a regular sub-expression.
+    getSubExpr()->print(OS, MAI, true);
+    return;
   case MEK_CALL_HI16:
     OS << "%call_hi";
     break;
@@ -160,7 +162,9 @@ MipsMCExpr::evaluateAsRelocatableImpl(MCValue &Res,
     case MEK_Special:
       llvm_unreachable("MEK_None and MEK_Special are invalid");
     case MEK_DTPREL:
-      llvm_unreachable("MEK_DTPREL is used for TLS DIEExpr only");
+      // MEK_DTPREL is used for marking TLS DIEExpr only
+      // and contains a regular sub-expression.
+      return getSubExpr()->evaluateAsRelocatable(Res, Layout, Fixup);
     case MEK_DTPREL_HI:
     case MEK_DTPREL_LO:
     case MEK_GOT:
@@ -248,9 +252,6 @@ void MipsMCExpr::fixELFSymbolsInTLSFixups(MCAssembler &Asm) const {
   case MEK_Special:
     llvm_unreachable("MEK_None and MEK_Special are invalid");
     break;
-  case MEK_DTPREL:
-    llvm_unreachable("MEK_DTPREL is used for TLS DIEExpr only");
-    break;
   case MEK_CALL_HI16:
   case MEK_CALL_LO16:
   case MEK_GOT:
@@ -273,6 +274,7 @@ void MipsMCExpr::fixELFSymbolsInTLSFixups(MCAssembler &Asm) const {
     if (const MipsMCExpr *E = dyn_cast<const MipsMCExpr>(getSubExpr()))
       E->fixELFSymbolsInTLSFixups(Asm);
     break;
+  case MEK_DTPREL:
   case MEK_DTPREL_HI:
   case MEK_DTPREL_LO:
   case MEK_TLSLDM: