[llvm] [BOLT] Modify warning when --use-old-text fails. NFC (PR #162731)

[Maksim Panchenko via llvm-commits]

https://github.com/maksfb created https://github.com/llvm/llvm-project/pull/162731

When --use-old-text fails, we are emitting all code meant for the original `.text` section into the new section. This could be more bytes compared to those emitted under no `--use-old-text`, especially under `--lite`. As a result, `--use-old-text` results in a larger binary, not smaller which could be confusing to the user.

Add more information to the warning, including recommendation to rebuild without `--use-old-text` for smaller binary size.

>From d293df1a8c62d8ad72714fc9879c8a9122f27b5f Mon Sep 17 00:00:00 2001
From: Maksim Panchenko <maks at fb.com>
Date: Thu, 9 Oct 2025 13:27:38 -0700
Subject: [PATCH] [BOLT] Modify warning when --use-old-text fails. NFC

When --use-old-text fails, we are emitting all code meant for the
original `.text` section into the new section. This could be more bytes
compared to those emitted under no `--use-old-text`, especially under
`--lite`. As a result, `--use-old-text` results in a larger binary, not
smaller which could be confusing to the user.

Add more information to the warning, including recommendation to rebuild
without `--use-old-text` for smaller binary size.
---
 bolt/lib/Rewrite/RewriteInstance.cpp | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index c428828956ca0..dad67175ad410 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -4005,10 +4005,12 @@ void RewriteInstance::mapCodeSections(BOLTLinker::SectionMapper MapSection) {
       BC->outs() << '\n';
       AllocationDone = true;
     } else {
-      BC->errs() << "BOLT-WARNING: original .text too small to fit the new code"
-                 << " using 0x" << Twine::utohexstr(opts::AlignText)
-                 << " alignment. " << CodeSize << " bytes needed, have "
-                 << BC->OldTextSectionSize << " bytes available.\n";
+      BC->errs() << "BOLT-WARNING: --use-old-text failed. The original .text "
+                    "too small to fit the new code using 0x"
+                 << Twine::utohexstr(opts::AlignText) << " alignment. "
+                 << CodeSize << " bytes needed, have " << BC->OldTextSectionSize
+                 << " bytes available. Rebuilding without --use-old-text may "
+                    "produce a smaller binary\n";
       opts::UseOldText = false;
     }
   }