From: Arthur Eubanks <aeubanks@google.com>
Date: Wed, 6 Oct 2021 20:57:29 +0000 (-0700)
Subject: Reland [clang] Pass -clear-ast-before-backend in Clang::ConstructJob()
X-Git-Tag: upstream/15.0.7~28018
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=19b07ec00062daffcb2fb132f4ac0f2484ff44fa;p=platform%2Fupstream%2Fllvm.git

Reland [clang] Pass -clear-ast-before-backend in Clang::ConstructJob()

This clears the memory used for the Clang AST before we run LLVM passes.

https://llvm-compile-time-tracker.com/compare.php?from=d0a5f61c4f6fccec87fd5207e3fcd9502dd59854&to=b7437fee79e04464dd968e1a29185495f3590481&stat=max-rss
shows significant memory savings with no slowdown (in fact -O0 slightly speeds up).

For more background, see
https://lists.llvm.org/pipermail/cfe-dev/2021-September/068930.html.

Turn this off for the interpreter since it does codegen multiple times.

Relanding with fix for -print-stats: D111973

Relanding with fix for plugins: D112190

If you'd like to use this even with plugins, consider using the features
introduced in D112096.

This can be turned off with -Xclang -no-clear-ast-before-backend.

Differential Revision: https://reviews.llvm.org/D111270
---

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 8dabfff..d5b5e3b 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -4675,6 +4675,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   // cleanup.
   if (!C.isForDiagnostics())
     CmdArgs.push_back("-disable-free");
+  CmdArgs.push_back("-clear-ast-before-backend");
 
 #ifdef NDEBUG
   const bool IsAssertBuild = false;
diff --git a/clang/lib/Interpreter/Interpreter.cpp b/clang/lib/Interpreter/Interpreter.cpp
index 02b3025..d14940d 100644
--- a/clang/lib/Interpreter/Interpreter.cpp
+++ b/clang/lib/Interpreter/Interpreter.cpp
@@ -113,6 +113,10 @@ CreateCI(const llvm::opt::ArgStringList &Argv) {
 
   Clang->getTarget().adjust(Clang->getDiagnostics(), Clang->getLangOpts());
 
+  // Don't clear the AST before backend codegen since we do codegen multiple
+  // times, reusing the same AST.
+  Clang->getCodeGenOpts().ClearASTBeforeBackend = false;
+
   return std::move(Clang);
 }