[PATCH] Fix PR18381 - print a minimal diagnostic rather than assert on unresolved .secidx target

[Timur Iskhodzhanov]

Hi echristo, rnk, grosbach,

http://llvm-reviews.chandlerc.com/D2653

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D2653?vs=6760&id=6779#toc

Files:
  include/llvm/MC/MCAssembler.h
  lib/MC/WinCOFFObjectWriter.cpp
  test/MC/COFF/secidx_diagnostic.s

Index: include/llvm/MC/MCAssembler.h
===================================================================
--- include/llvm/MC/MCAssembler.h
+++ include/llvm/MC/MCAssembler.h
@@ -1153,6 +1153,10 @@
     return *Entry;
   }
 
+  bool hasSymbolData(const MCSymbol &Symbol) const {
+    return SymbolMap.lookup(&Symbol) != 0;
+  }
+
   MCSymbolData &getSymbolData(const MCSymbol &Symbol) const {
     MCSymbolData *Entry = SymbolMap.lookup(&Symbol);
     assert(Entry && "Missing symbol data!");
Index: lib/MC/WinCOFFObjectWriter.cpp
===================================================================
--- lib/MC/WinCOFFObjectWriter.cpp
+++ lib/MC/WinCOFFObjectWriter.cpp
@@ -636,6 +636,11 @@
 
   const MCSymbol &Symbol = Target.getSymA()->getSymbol();
   const MCSymbol &A = Symbol.AliasedSymbol();
+  if (!Asm.hasSymbolData(A))
+    Asm.getContext().FatalError(
+        Fixup.getLoc(),
+        Twine("symbol '") + A.getName() + "' can not be undefined");
+
   MCSymbolData &A_SD = Asm.getSymbolData(A);
 
   MCSectionData const *SectionData = Fragment->getParent();
Index: test/MC/COFF/secidx_diagnostic.s
===================================================================
--- test/MC/COFF/secidx_diagnostic.s
+++ test/MC/COFF/secidx_diagnostic.s
@@ -1,8 +1,8 @@
 // RUN: not llvm-mc -filetype=obj -triple i686-pc-win32 %s 2>%t
 // RUN: FileCheck %s < %t
 
-// CHECK: Can't resolve the 'bar at 2' symbol
+// CHECK: symbol 'bar' can not be undefined
 
 .data
 foo:
-        .secidx bar at 2
+        .secidx bar
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