Index: bolt/include/bolt/Core/BinaryFunction.h
===================================================================
--- bolt/include/bolt/Core/BinaryFunction.h
+++ bolt/include/bolt/Core/BinaryFunction.h
@@ -370,7 +370,8 @@
   BinaryFunction *FoldedIntoFunction{nullptr};
 
   /// All fragments for a parent function.
-  SmallPtrSet<BinaryFunction *, 1> Fragments;
+  using FragmentsSetTy = SmallPtrSet<BinaryFunction *, 1>;
+  FragmentsSetTy Fragments;
 
   /// The profile data for the number of times the function was executed.
   uint64_t ExecutionCount{COUNT_NO_PROFILE};
@@ -1768,6 +1769,12 @@
     return llvm::is_contained(Fragments, &Other);
   }
 
+  /// Return the child fragment form parent function
+  iterator_range<FragmentsSetTy::const_iterator> getFragments() const {
+    return iterator_range<FragmentsSetTy::const_iterator>(Fragments.begin(),
+                                                          Fragments.end());
+  }
+
   /// Returns if this function is a parent or child of \p Other function.
   bool isParentOrChildOf(const BinaryFunction &Other) const {
     return isChildOf(Other) || isParentOf(Other);
Index: bolt/lib/Passes/RegReAssign.cpp
===================================================================
--- bolt/lib/Passes/RegReAssign.cpp
+++ bolt/lib/Passes/RegReAssign.cpp
@@ -304,6 +304,10 @@
                       << " with " << BC.MRI->getName(ExtReg) << "\n\n");
     swap(Function, ClassicReg, ExtReg);
     FuncsChanged.insert(&Function);
+    for (BinaryFunction *ChildFrag : Function.getFragments()) {
+      swap(*ChildFrag, ClassicReg, ExtReg);
+      FuncsChanged.insert(ChildFrag);
+    }
     ++Begin;
     if (Begin == End)
       break;
@@ -345,6 +349,10 @@
   (void)BC;
   swap(Function, RBX, Candidate);
   FuncsChanged.insert(&Function);
+  for (BinaryFunction *ChildFrag : Function.getFragments()) {
+    swap(*ChildFrag, RBX, Candidate);
+    FuncsChanged.insert(ChildFrag);
+  }
   return true;
 }
 
@@ -404,7 +412,7 @@
   for (auto &I : BC.getBinaryFunctions()) {
     BinaryFunction &Function = I.second;
 
-    if (!Function.isSimple() || Function.isIgnored())
+    if (!Function.isSimple() || Function.isIgnored() || Function.isFragment())
       continue;
 
     LLVM_DEBUG(dbgs() << "====================================\n");
Index: bolt/test/X86/reg-reassign-swap-cold.s
===================================================================
--- /dev/null
+++ bolt/test/X86/reg-reassign-swap-cold.s
@@ -0,0 +1,66 @@
+# This test case reproduces a bug where, during register swapping, 
+# the code fragments associated with the function need to be swapped
+# together (which may be generated during PGO optimization). If not
+# handled properly, optimized binary execution can result in a segmentation fault.
+
+# REQUIRES: system-linux
+
+# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
+# RUN: link_fdata %s %t.o %t.fdata
+# RUN: %clang -no-pie %t.o -o %t.exe -Wl,-q
+# RUN: llvm-bolt %t.exe -o %t.out -data=%t.fdata --reg-reassign | FileCheck %s
+# RUN: %t.out
+
+# CHECK: BOLT-INFO: Reg Reassignment Pass Stats
+# CHECK-NEXT: 2 functions affected.
+	.text
+	.file	"a.c"
+	.globl	main														# -- Begin function main
+	.p2align	4, 0x90
+	.type	main,@function
+	.type	main.cold,@function
+main.cold:
+.L1:
+	leaq	.Lstr(%rip), %rdi
+				callq	 puts@PLT
+				mov		$113, %rbx
+				jmp		 .L3
+main:																	 # @main
+	.cfi_startproc
+# %bb.0:																# %entry
+	pushq	%rax
+				pushq	 %r15
+				pushq	 %rbx
+	.cfi_def_cfa_offset 16
+				mov		 $1,	 %r15
+				mov		 $111, %rbx
+.L2:
+				jmp		 .L1
+				add		 $1,	 %r15
+.L3:
+				cmp		 $113, %r15
+				je			.Lstr
+	xorl	%eax, %eax
+	popq	%rcx
+				popq		%rbx
+				popq		%r15
+	.cfi_def_cfa_offset 8
+	retq
+# FDATA: 1 main.cold/1 7 1 puts@PLT 0 0 1
+# FDATA: 1 main.cold/1 13 1 main 0 0 100
+# FDATA: 1 main 1c 1 main 22 0 100
+# FDATA: 1 main 12 1 main.cold/1 0 0 100
+
+.Lfunc_end0:
+	.size	main, .Lfunc_end0-main
+	.cfi_endproc
+																				# -- End function
+	.type	.Lstr,@object									 # @str
+	.section	.rodata.str1.1,"aMS",@progbits,1
+.Lstr:
+	.asciz	"success"
+	.size	.Lstr, 8
+
+	.ident	"clang version 15.0.4 (8589d40d00b8)"
+	.section	".note.GNU-stack","",@progbits
+	.addrsig