Use a SmallString buffer instead of a std::string for debug info path lookup. NFC.

This code appends the filename to the directory then looks that up in a StringMap.  We should be using the existing Twine::toStringRef method instead of Twine::str() as most times we'll succeed in the lookup.

Its possible that we should also consider allowing StringMap to lookup a key using a Twine in addition to a StringRef but that would complicate the code with little known benefit above and beyond this change.

This saves 170k temporary allocations when running llc on the verify_use_list_order bitcode with debug info for x86.

llvm-svn: 237823

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/MC/MCDwarf.cpp b/llvm/lib/MC/MCDwarf.cpp
index 05c2a02a8ed..74eee83b73f 100644
--- a/llvm/lib/MC/MCDwarf.cpp
+++ b/llvm/lib/MC/MCDwarf.cpp
@@ -360,8 +360,10 @@ unsigned MCDwarfLineTableHeader::getFile(StringRef &Directory,
     FileNumber = SourceIdMap.size() + 1;
     assert((MCDwarfFiles.empty() || FileNumber == MCDwarfFiles.size()) &&
            "Don't mix autonumbered and explicit numbered line table usage");
+    SmallString<256> Buffer;
     auto IterBool = SourceIdMap.insert(
-        std::make_pair((Directory + Twine('\0') + FileName).str(), FileNumber));
+        std::make_pair((Directory + Twine('\0') + FileName).toStringRef(Buffer),
+                       FileNumber));
     if (!IterBool.second)
       return IterBool.first->second;
   }