From 5e14916fa6ab8dbafd06f4d3b7b8f9eb3abb767d Mon Sep 17 00:00:00 2001
From: Yashwant Singh <yashwants@nvidia.com>
Date: Mon, 6 Apr 2026 09:37:05 +0530
Subject: [PATCH] Early exit llvm-bolt when coming across empty data files
 (#176859)

perf2bolt generates empty fdata files for small binaries and right now
BOLT does this check while parsing by calling `((!hasBranchData() &&
!hasMemData()))`. Instead, early exit as soon as the buffer finishes
reading the data file and exit with error message.
---
 bolt/lib/Profile/DataReader.cpp | 12 +++++++++---
 bolt/test/empty-fdata-file.test | 12 ++++++++++++
 2 files changed, 21 insertions(+), 3 deletions(-)
 create mode 100644 bolt/test/empty-fdata-file.test

diff --git a/bolt/lib/Profile/DataReader.cpp b/bolt/lib/Profile/DataReader.cpp
index 2e0c094b371b..ef4a65bb03b9 100644
--- a/bolt/lib/Profile/DataReader.cpp
+++ b/bolt/lib/Profile/DataReader.cpp
@@ -315,11 +315,17 @@ std::error_code DataReader::parseInput() {
   }
   FileBuf = std::move(MB.get());
   ParsingBuf = FileBuf->getBuffer();
+
+  if (ParsingBuf.empty()) {
+    Diag << "WARNING: empty profile data file: " << Filename << "\n";
+    return make_error_code(llvm::errc::io_error);
+  }
+
   if (std::error_code EC = parse())
     return EC;
-  if (!ParsingBuf.empty())
-    Diag << "WARNING: invalid profile data detected at line " << Line
-         << ". Possibly corrupted profile.\n";
+
+  Diag << "WARNING: invalid profile data detected at line " << Line
+       << ". Possibly corrupted profile.\n";
 
   buildLTONameMaps();
 
diff --git a/bolt/test/empty-fdata-file.test b/bolt/test/empty-fdata-file.test
new file mode 100644
index 000000000000..b7e5f63c9fc9
--- /dev/null
+++ b/bolt/test/empty-fdata-file.test
@@ -0,0 +1,12 @@
+## Check that llvm-bolt detects bad profile data and aborts
+
+## This test uses the clang driver without target flags and will only succeed
+## on Linux systems where the host triple matches the target.
+REQUIRES: system-linux
+
+RUN: %clang %cflags %S/Inputs/hello.c -o %t
+RUN: touch %t.empty.fdata
+RUN: not llvm-bolt %t -o %t.bolt --data %t.empty.fdata 2>&1 | FileCheck %s
+
+CHECK: WARNING: empty profile data file
+CHECK-NEXT: BOLT-ERROR: {{.*}}Input/output error