Reapply "[DebugInfo] Alternate (more efficient) MD5 fix"

D155991 changed the file lookup to do a full string compare on the
filename; however, this added ~0.5% to compile time with -g.
Go back to the previous pointer-based lookup, but capture the main
file's checksum as well as its name to use when creating the extra
DIFile entry. This causes all entries to be consistent and also
avoids computing the checksum twice.

This reverts commit 5956648fc3ba11dd6b0d0f2d1d9b923e7f80f247.
There was a string lifetime issue that is now corrected.

Differential Revision: https://reviews.llvm.org/D156571

2 files changed, 9 insertions, 6 deletions

diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 54e31be..36e2928 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -391,12 +391,14 @@ llvm::DIFile *CGDebugInfo::getOrCreateFile(SourceLocation Loc) {
   SourceManager &SM = CGM.getContext().getSourceManager();
   StringRef FileName;
   FileID FID;
+  std::optional<llvm::DIFile::ChecksumInfo<StringRef>> CSInfo;
 
   if (Loc.isInvalid()) {
     // The DIFile used by the CU is distinct from the main source file. Call
     // createFile() below for canonicalization if the source file was specified
     // with an absolute path.
     FileName = TheCU->getFile()->getFilename();
+    CSInfo = TheCU->getFile()->getChecksum();
   } else {
     PresumedLoc PLoc = SM.getPresumedLoc(Loc);
     FileName = PLoc.getFilename();
@@ -417,13 +419,14 @@ llvm::DIFile *CGDebugInfo::getOrCreateFile(SourceLocation Loc) {
       return cast<llvm::DIFile>(V);
   }
 
+  // Put Checksum at a scope where it will persist past the createFile call.
   SmallString<64> Checksum;
-
-  std::optional<llvm::DIFile::ChecksumKind> CSKind =
+  if (!CSInfo) {
+    std::optional<llvm::DIFile::ChecksumKind> CSKind =
       computeChecksum(FID, Checksum);
-  std::optional<llvm::DIFile::ChecksumInfo<StringRef>> CSInfo;
-  if (CSKind)
-    CSInfo.emplace(*CSKind, Checksum);
+    if (CSKind)
+      CSInfo.emplace(*CSKind, Checksum);
+  }
   return createFile(FileName, CSInfo, getSource(SM, SM.getFileID(Loc)));
 }
 
diff --git a/clang/lib/CodeGen/CGDebugInfo.h b/clang/lib/CodeGen/CGDebugInfo.h
index ec84379..b47a493 100644
--- a/clang/lib/CodeGen/CGDebugInfo.h
+++ b/clang/lib/CodeGen/CGDebugInfo.h
@@ -148,7 +148,7 @@ class CGDebugInfo {
   llvm::BumpPtrAllocator DebugInfoNames;
   StringRef CWDName;
 
-  llvm::StringMap<llvm::TrackingMDRef> DIFileCache;
+  llvm::DenseMap<const char *, llvm::TrackingMDRef> DIFileCache;
   llvm::DenseMap<const FunctionDecl *, llvm::TrackingMDRef> SPCache;
   /// Cache declarations relevant to DW_TAG_imported_declarations (C++
   /// using declarations and global alias variables) that aren't covered