[PATCH] D148852: [Demangle] fix windows tests

[Nick Desaulniers via Phabricator via llvm-commits]

nickdesaulniers created this revision.
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My reland of https://reviews.llvm.org/D148546 has caused a few windows
demangler tests to fail when run with -DLLVM_ENABLE_EXPENSIVE_CHECKS=ON
on windows.

I have a sneaking suspicion that MSVC's
std::string_view::iterator::operator* may be missing a nullptr check.

Link: https://lab.llvm.org/buildbot/#/builders/42/builds/9723/steps/7/logs/stdio


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D148852

Files:
  llvm/lib/Demangle/MicrosoftDemangle.cpp


Index: llvm/lib/Demangle/MicrosoftDemangle.cpp
===================================================================
--- llvm/lib/Demangle/MicrosoftDemangle.cpp
+++ llvm/lib/Demangle/MicrosoftDemangle.cpp
@@ -793,6 +793,7 @@
     return nullptr;
   }
   const char *Start = &*MangledName.begin();
+  const size_t StartSize = MangledName.size();
   MangledName.remove_prefix(MD5Last + 1);
 
   // There are two additional special cases for MD5 names:
@@ -807,7 +808,8 @@
   //    either.
   consumeFront(MangledName, "??_R4@");
 
-  std::string_view MD5(Start, &*MangledName.begin() - Start);
+  const size_t Count = MangledName.size() - StartSize;
+  std::string_view MD5(Start, Count);
   SymbolNode *S = Arena.alloc<SymbolNode>(NodeKind::Md5Symbol);
   S->Name = synthesizeQualifiedName(Arena, MD5);
 
@@ -2402,7 +2404,7 @@
   std::string_view Name{MangledName};
   SymbolNode *AST = D.parse(Name);
   if (!D.Error && NMangled)
-    *NMangled = &*Name.begin() - MangledName;
+    *NMangled = Name.empty() ? 0 : &*Name.begin() - MangledName;
 
   if (Flags & MSDF_DumpBackrefs)
     D.dumpBackReferences();


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