[llvm] 9554aaa - [Dwarf] Optimize getOrCreateSourceID() for repeated calls on same file (NFCI)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2022-01-25T09:27:11+01:00
New Revision: 9554aaa2753bd866a00bf6fb4183656200e758e2

URL: https://github.com/llvm/llvm-project/commit/9554aaa2753bd866a00bf6fb4183656200e758e2
DIFF: https://github.com/llvm/llvm-project/commit/9554aaa2753bd866a00bf6fb4183656200e758e2.diff

LOG: [Dwarf] Optimize getOrCreateSourceID() for repeated calls on same file (NFCI)

DwarfCompileUnit::getOrCreateSourceID() is often called many times
in sequence with the same DIFile. This is currently very expensive,
because it involves creating a string from directory and file name
and looking it up in a string map. This patch remembers the last
DIFile and its ID and directly returns that.

This gives a geomean -1.3% compile-time improvement on CTMark O0-g.

Differential Revision: https://reviews.llvm.org/D118041

Added: 
    

Modified: 
    llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
    llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index ab3c9f486670e..5913c687db48f 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -127,9 +127,14 @@ unsigned DwarfCompileUnit::getOrCreateSourceID(const DIFile *File) {
   if (!File)
     return Asm->OutStreamer->emitDwarfFileDirective(0, "", "", None, None,
                                                     CUID);
-  return Asm->OutStreamer->emitDwarfFileDirective(
-      0, File->getDirectory(), File->getFilename(), DD->getMD5AsBytes(File),
-      File->getSource(), CUID);
+
+  if (LastFile != File) {
+    LastFile = File;
+    LastFileID = Asm->OutStreamer->emitDwarfFileDirective(
+        0, File->getDirectory(), File->getFilename(), DD->getMD5AsBytes(File),
+        File->getSource(), CUID);
+  }
+  return LastFileID;
 }
 
 DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(

diff  --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
index fb03982b5e4a2..f2e1f63468039 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
@@ -86,6 +86,9 @@ class DwarfCompileUnit final : public DwarfUnit {
   /// DWO ID for correlating skeleton and split units.
   uint64_t DWOId = 0;
 
+  const DIFile *LastFile = nullptr;
+  unsigned LastFileID;
+
   /// Construct a DIE for the given DbgVariable without initializing the
   /// DbgVariable's DIE reference.
   DIE *constructVariableDIEImpl(const DbgVariable &DV, bool Abstract);