[Demangle] convert itaniumDemangle and nonMicrosoftDemangle to use std::string_view

D149104 converted llvm::demangle to use std::string_view. Enabling
"expensive checks" (via -DLLVM_ENABLE_EXPENSIVE_CHECKS=ON) causes
lld/test/wasm/why-extract.s to fail. The reason for this is obscure:

Reason #10007 why std::string_view is dangerous:
Consider the following pattern:

  std::string_view s = ...;
  const char *c = s.data();
  std::strlen(c);

Is c a NUL-terminated C style string? It depends; but if it's not then
it's not safe to call std::strlen on the std::string_view::data().
std::string_view::length() should be used instead.

Fixing this fixes the one lone test that caught this.

microsoftDemangle, rustDemangle, and dlangDemangle should get this same
treatment, too. I will do that next.

Reviewed By: MaskRay, efriedma

Differential Revision: https://reviews.llvm.org/D149675

1 files changed, 6 insertions, 4 deletions

diff --git a/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp b/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
index 109c1b2..2bbd57f 100644
--- a/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
+++ b/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
@@ -8,6 +8,7 @@
 
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Demangle/Demangle.h"
+#include "llvm/Demangle/StringViewExtras.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Option/Option.h"
@@ -71,10 +72,11 @@ static void error(const Twine &Message) {
 }
 
 static std::string demangle(const std::string &Mangled) {
-  const char *DecoratedStr = Mangled.c_str();
+  using llvm::itanium_demangle::starts_with;
+  std::string_view DecoratedStr = Mangled;
   if (StripUnderscore)
     if (DecoratedStr[0] == '_')
-      ++DecoratedStr;
+      DecoratedStr.remove_prefix(1);
 
   std::string Result;
   if (nonMicrosoftDemangle(DecoratedStr, Result))
@@ -86,9 +88,9 @@ static std::string demangle(const std::string &Mangled) {
   if (Types)
     Undecorated = itaniumDemangle(DecoratedStr);
 
-  if (!Undecorated && strncmp(DecoratedStr, "__imp_", 6) == 0) {
+  if (!Undecorated && starts_with(DecoratedStr, "__imp_")) {
     Prefix = "import thunk for ";
-    Undecorated = itaniumDemangle(DecoratedStr + 6);
+    Undecorated = itaniumDemangle(DecoratedStr.substr(6));
   }
 
   Result = Undecorated ? Prefix + Undecorated : Mangled;