Index: llvm/trunk/lib/Target/X86/X86FrameLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/X86/X86FrameLowering.cpp
+++ llvm/trunk/lib/Target/X86/X86FrameLowering.cpp
@@ -1381,6 +1381,18 @@
     if (PushedRegs)
       emitCalleeSavedFrameMoves(MBB, MBBI, DL);
   }
+
+  // X86 Interrupt handling function cannot assume anything about the direction
+  // flag (DF in EFLAGS register). Clear this flag by creating "cld" instruction
+  // in each prologue of interrupt handler function.
+  //
+  // FIXME: Create "cld" instruction only in these cases:
+  // 1. The interrupt handling function uses any of the "rep" instructions.
+  // 2. Interrupt handling function calls another function.
+  //
+  if (Fn->getCallingConv() == CallingConv::X86_INTR)
+    BuildMI(MBB, MBBI, DL, TII.get(X86::CLD))
+        .setMIFlag(MachineInstr::FrameSetup);
 }
 
 bool X86FrameLowering::canUseLEAForSPInEpilogue(
Index: llvm/trunk/test/CodeGen/X86/x86-interrupt_cld.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/x86-interrupt_cld.ll
+++ llvm/trunk/test/CodeGen/X86/x86-interrupt_cld.ll
@@ -0,0 +1,17 @@
+; RUN: llc -mtriple=x86_64-unknown-unknown < %s | FileCheck %s
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Checks that interrupt handler code calls cld before calling an external
+;; function.
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+; CHECK: cld
+; CHECK: call
+
+define x86_intrcc void @foo(i8* %frame) {
+  call void @bar()
+  ret void
+}
+
+declare void @bar()
+