[llvm] [DebugInfo] Only call upgradeCULocals() at module level (PR #68965)

[Nikita Popov via llvm-commits]

https://github.com/nikic created https://github.com/llvm/llvm-project/pull/68965

Loading a 2GB bitcode file, I noticed that we spend minutes just running upgradeCULocals(). Apparently it gets invoked every time a metadata block is loaded, which will be once at the module level and then once per function. However, the relevant metadata only exists at the module level, so running this upgrade per function is unnecessary.

>From 18eade4c66bbb1f993a2a28f51b59d294cd4f8af Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Fri, 13 Oct 2023 11:18:31 +0200
Subject: [PATCH] [DebugInfo] Only call upgradeCULocals() at module level

Loading a 2GB bitcode file, I noticed that we spend minutes just
running upgradeCULocals(). Apparently it gets invoked every time
a metadata block is loaded, which will be once at the module
level and then once per function. However, the relevant metadata
only exists at the module level, so running this upgrade per
function is unnecessary.
---
 llvm/lib/Bitcode/Reader/MetadataLoader.cpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Bitcode/Reader/MetadataLoader.cpp b/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
index 1e9ed5fcaa581b3..4aaaea7ffeed423 100644
--- a/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
+++ b/llvm/lib/Bitcode/Reader/MetadataLoader.cpp
@@ -705,10 +705,11 @@ class MetadataLoader::MetadataLoaderImpl {
     return Error::success();
   }
 
-  void upgradeDebugInfo() {
+  void upgradeDebugInfo(bool ModuleLevel) {
     upgradeCUSubprograms();
     upgradeCUVariables();
-    upgradeCULocals();
+    if (ModuleLevel)
+      upgradeCULocals();
   }
 
   void callMDTypeCallback(Metadata **Val, unsigned TypeID);
@@ -1085,7 +1086,7 @@ Error MetadataLoader::MetadataLoaderImpl::parseMetadata(bool ModuleLevel) {
       // Reading the named metadata created forward references and/or
       // placeholders, that we flush here.
       resolveForwardRefsAndPlaceholders(Placeholders);
-      upgradeDebugInfo();
+      upgradeDebugInfo(ModuleLevel);
       // Return at the beginning of the block, since it is easy to skip it
       // entirely from there.
       Stream.ReadBlockEnd(); // Pop the abbrev block context.
@@ -1116,7 +1117,7 @@ Error MetadataLoader::MetadataLoaderImpl::parseMetadata(bool ModuleLevel) {
       return error("Malformed block");
     case BitstreamEntry::EndBlock:
       resolveForwardRefsAndPlaceholders(Placeholders);
-      upgradeDebugInfo();
+      upgradeDebugInfo(ModuleLevel);
       return Error::success();
     case BitstreamEntry::Record:
       // The interesting case.