[mips] Fix TestDWARF32Version5Addr8AllForms test failure on MIPS hosts

The `DIEExpr` is used in debug information entries for either TLS variables
or call sites. For now the last case is unsupported for targets with delay
slots, for MIPS in particular.

The `DIEExpr::EmitValue` method calls a virtual `EmitDebugThreadLocal`
routine which, in case of MIPS, always emits either `.dtprelword` or
`.dtpreldword` directives. That is okay for "main" code, but in unit
tests `DIEExpr` instances can be created not for TLS variables only even
on MIPS hosts. That is a reason of the `TestDWARF32Version5Addr8AllForms`
failure because handling of the `R_MIPS_TLS_DTPREL` relocation writes
incorrect value into dwarf structures. And anyway unconditional emitting
of `.dtprelword` directives will be incorrect when/if debug information
entries for call sites become supported on MIPS.

The patch solves the problem by wrapping expression created in the
`MipsTargetObjectFile::getDebugThreadLocalSymbol` method in to the
`MipsMCExpr` expression with a new `MEK_DTPREL` tag. This tag is
recognized in the `MipsAsmPrinter::EmitDebugThreadLocal` method and
`.dtprelword` directives created in this case only. In other cases the
expression saved as a regular data.

Differential Revision: http://reviews.llvm.org/D54937

llvm-svn: 348194

llvm/lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp

@@ -613,6 +613,9 @@ getExprOpValue(const MCExpr *Expr, SmallVectorImpl<MCFixup> &Fixups,
     case MipsMCExpr::MEK_Special:
       llvm_unreachable("Unhandled fixup kind!");
       break;
+    case MipsMCExpr::MEK_DTPREL:
+      llvm_unreachable("MEK_DTPREL is used for TLS DIEExpr only");
+      break;
     case MipsMCExpr::MEK_CALL_HI16:
       FixupKind = Mips::fixup_Mips_CALL_HI16;
       break;

llvm/lib/Target/Mips/MCTargetDesc/MipsMCExpr.cpp

@@ -43,6 +43,9 @@ void MipsMCExpr::printImpl(raw_ostream &OS, const MCAsmInfo *MAI) 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:
     OS << "%call_hi";
     break;
@@ -157,6 +160,8 @@ MipsMCExpr::evaluateAsRelocatableImpl(MCValue &Res,
     case MEK_None:
     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");
     case MEK_DTPREL_HI:
     case MEK_DTPREL_LO:
     case MEK_GOT:
@@ -244,6 +249,9 @@ 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:

llvm/lib/Target/Mips/MCTargetDesc/MipsMCExpr.h

@@ -22,6 +22,7 @@ public:
     MEK_None,
     MEK_CALL_HI16,
     MEK_CALL_LO16,
+    MEK_DTPREL,
     MEK_DTPREL_HI,
     MEK_DTPREL_LO,
     MEK_GOT,

llvm/lib/Target/Mips/MipsAsmPrinter.cpp

@@ -1205,16 +1205,22 @@ void MipsAsmPrinter::PrintDebugValueComment(const MachineInstr *MI,
 // Emit .dtprelword or .dtpreldword directive
 // and value for debug thread local expression.
 void MipsAsmPrinter::EmitDebugValue(const MCExpr *Value, unsigned Size) const {
-  switch (Size) {
-  case 4:
-    OutStreamer->EmitDTPRel32Value(Value);
-    break;
-  case 8:
-    OutStreamer->EmitDTPRel64Value(Value);
-    break;
-  default:
-    llvm_unreachable("Unexpected size of expression value.");
+  if (auto *MipsExpr = dyn_cast<MipsMCExpr>(Value)) {
+    if (MipsExpr && MipsExpr->getKind() == MipsMCExpr::MEK_DTPREL) {
+      switch (Size) {
+      case 4:
+        OutStreamer->EmitDTPRel32Value(MipsExpr->getSubExpr());
+        break;
+      case 8:
+        OutStreamer->EmitDTPRel64Value(MipsExpr->getSubExpr());
+        break;
+      default:
+        llvm_unreachable("Unexpected size of expression value.");
+      }
+      return;
+    }
   }
+  AsmPrinter::EmitDebugValue(Value, Size);
 }
 
 // Align all targets of indirect branches on bundle size.  Used only if target

llvm/lib/Target/Mips/MipsTargetObjectFile.cpp

@@ -10,6 +10,7 @@
 #include "MipsTargetObjectFile.h"
 #include "MipsSubtarget.h"
 #include "MipsTargetMachine.h"
+#include "MCTargetDesc/MipsMCExpr.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DerivedTypes.h"
@@ -189,6 +190,7 @@ const MCExpr *
 MipsTargetObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
   const MCExpr *Expr =
       MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_None, getContext());
-  return MCBinaryExpr::createAdd(
+  Expr = MCBinaryExpr::createAdd(
       Expr, MCConstantExpr::create(0x8000, getContext()), getContext());
+  return MipsMCExpr::create(MipsMCExpr::MEK_DTPREL, Expr, getContext());
 }