[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

1 files changed, 15 insertions, 9 deletions

diff --git a/llvm/lib/Target/Mips/MipsAsmPrinter.cpp b/llvm/lib/Target/Mips/MipsAsmPrinter.cpp
index 75d01a05b91..362431fd42a 100644
--- a/llvm/lib/Target/Mips/MipsAsmPrinter.cpp
+++ b/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