From 1e5493b1b84473e42bc9992f6684e51eeb335f14 Mon Sep 17 00:00:00 2001
From: Maksim Panchenko <maks@fb.com>
Date: Sat, 7 Feb 2026 20:39:24 -0800
Subject: [PATCH] [BOLT] Don't fold hot text mover functions in ICF (#180367)

Hot text mover functions are placed in special sections (e.g.,
.never_hugify) to avoid being placed on hot/huge pages. Folding them
with functions from other sections could defeat this purpose.

Add a check in ICF's isIdenticalWith() to prevent folding when either
function is a hot text mover.
---
 bolt/lib/Passes/IdenticalCodeFolding.cpp |  7 +++++++
 bolt/test/icf-hot-text-mover.c           | 24 ++++++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 bolt/test/icf-hot-text-mover.c

diff --git a/bolt/lib/Passes/IdenticalCodeFolding.cpp b/bolt/lib/Passes/IdenticalCodeFolding.cpp
index b63bab75540b..1c99a60bfaad 100644
--- a/bolt/lib/Passes/IdenticalCodeFolding.cpp
+++ b/bolt/lib/Passes/IdenticalCodeFolding.cpp
@@ -33,6 +33,8 @@ namespace opts {
 
 extern cl::OptionCategory BoltOptCategory;
 
+extern bool isHotTextMover(const BinaryFunction &Function);
+
 static cl::opt<bool>
     ICFUseDFS("icf-dfs", cl::desc("use DFS ordering when using -icf option"),
               cl::ReallyHidden, cl::cat(BoltOptCategory));
@@ -186,6 +188,11 @@ static bool isIdenticalWith(const BinaryFunction &A, const BinaryFunction &B,
                             bool CongruentSymbols) {
   assert(A.hasCFG() && B.hasCFG() && "both functions should have CFG");
 
+  // Hot text mover functions should not be folded. They need to stay in their
+  // original section to avoid being placed on hot/huge pages.
+  if (opts::isHotTextMover(A) || opts::isHotTextMover(B))
+    return false;
+
   // Compare the two functions, one basic block at a time.
   // Currently we require two identical basic blocks to have identical
   // instruction sequences and the same index in their corresponding
diff --git a/bolt/test/icf-hot-text-mover.c b/bolt/test/icf-hot-text-mover.c
new file mode 100644
index 000000000000..3ecfe9b2c135
--- /dev/null
+++ b/bolt/test/icf-hot-text-mover.c
@@ -0,0 +1,24 @@
+// Check that ICF does not fold hot text mover functions.
+// Hot text mover functions are placed in special sections (e.g., .never_hugify)
+// to avoid being placed on hot/huge pages.
+
+// clang-format off
+
+// REQUIRES: system-linux, asserts
+// RUN: %clang %cflags -O0 %s -o %t.exe -Wl,-q
+// RUN: llvm-bolt %t.exe --icf --hot-text-move-sections=.never_hugify \
+// RUN:   -debug-only=bolt-icf -o %t.bolt 2>&1 | FileCheck %s
+
+// FuncA is in .text, FuncB is in .never_hugify (a hot text mover section).
+// They are identical, but FuncB should NOT be folded because it is a hot text mover.
+// CHECK: ICF iteration 1
+// CHECK-NOT: folding FuncB into FuncA
+// CHECK-NOT: folding FuncA into FuncB
+
+__attribute__((noinline)) int FuncA(void) { return 42; }
+
+__attribute__((section(".never_hugify"), noinline)) int FuncB(void) {
+  return 42;
+}
+
+int main(void) { return FuncA() + FuncB(); }