From: Pete Cooper <peter_cooper@apple.com>
Date: Wed, 20 May 2015 19:12:14 +0000 (+0000)
Subject: Use a SmallString buffer instead of a std::string for debug info path lookup.  NFC.
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=bed96c8d97e72a3773606b714bb42037b6cf9a6b;p=oota-llvm.git

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 05c2a02a8ed..74eee83b73f 100644
--- 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;
   }