[llvm] [BOLT] Always run CheckLargeFunctions in non-relocation mode (PR #80922)

[Maksim Panchenko via llvm-commits]

https://github.com/maksfb created https://github.com/llvm/llvm-project/pull/80922

We run CheckLargeFunctions pass in non-relocation mode to prevent the emission of functions that later could not be written to the output due to their large size. The main reason behind the pass is to prevent the emission of metadata for such functions since this metadata becomes incorrect if the function is left unmodified.

Currently, the pass is enabled in non-relocation mode only when debug info output is also enabled. As we emit increasingly more kinds of metadata, e.g. for the Linux kernel, it becomes more challenging to track metadata that needs to be fixed. Hence, I'm enabling the pass to always run in non-relocation mode.

>From 85604388c62a03c4d070e5bb7ffe1778ba29c6c6 Mon Sep 17 00:00:00 2001
From: Maksim Panchenko <maks at fb.com>
Date: Tue, 6 Feb 2024 15:01:38 -0800
Subject: [PATCH] [BOLT] Always run CheckLargeFunctions in non-relocation mode

We run CheckLargeFunctions pass in non-relocation mode to prevent the
emission of functions that later could not be written to the output due
to their large size. The main reason behind the pass is to prevent the
emission of metadata for such functions since this metadata becomes
incorrect if the function is left unmodified.

Currently, the pass is enabled in non-relocation mode only when debug
info output is also enabled. As we emit increasingly more kinds of
metadata, e.g. for the Linux kernel, it becomes more challenging to
track metadata that needs to be fixed. Hence, I'm enabling the pass to
always run in non-relocation mode.
---
 bolt/lib/Passes/BinaryPasses.cpp     | 5 +----
 bolt/lib/Rewrite/RewriteInstance.cpp | 2 ++
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/bolt/lib/Passes/BinaryPasses.cpp b/bolt/lib/Passes/BinaryPasses.cpp
index 8505d37491415..cdfe9c642eb74 100644
--- a/bolt/lib/Passes/BinaryPasses.cpp
+++ b/bolt/lib/Passes/BinaryPasses.cpp
@@ -554,11 +554,8 @@ void CheckLargeFunctions::runOnFunctions(BinaryContext &BC) {
   if (BC.HasRelocations)
     return;
 
-  if (!opts::UpdateDebugSections)
-    return;
-
   // If the function wouldn't fit, mark it as non-simple. Otherwise, we may emit
-  // incorrect debug info.
+  // incorrect meta data.
   ParallelUtilities::WorkFuncTy WorkFun = [&](BinaryFunction &BF) {
     uint64_t HotSize, ColdSize;
     std::tie(HotSize, ColdSize) =
diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index 0fa5dcee64a32..b3e2da50413bf 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -3631,6 +3631,7 @@ void RewriteInstance::mapCodeSections(BOLTLinker::SectionMapper MapSection) {
     Function.setImageAddress(FuncSection->getAllocAddress());
     Function.setImageSize(FuncSection->getOutputSize());
     if (Function.getImageSize() > Function.getMaxSize()) {
+      assert(!BC->isX86() && "Unexpected large function.");
       TooLarge = true;
       FailedAddresses.emplace_back(Function.getAddress());
     }
@@ -5367,6 +5368,7 @@ void RewriteInstance::rewriteFile() {
       continue;
 
     if (Function->getImageSize() > Function->getMaxSize()) {
+      assert(!BC->isX86() && "Unexpected large function.");
       if (opts::Verbosity >= 1)
         errs() << "BOLT-WARNING: new function size (0x"
                << Twine::utohexstr(Function->getImageSize())