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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237823 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
index 05c2a02a8ed2e3a98142db2c25a6ecb2f0cb8280..74eee83b73fb85a059c41f5ba52923bd448744a5 100644 (file)
--- a/lib/MC/MCDwarf.cpp
+++ b/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;
   }