Index: lib/Transforms/IPO/ArgumentPromotion.cpp
===================================================================
--- lib/Transforms/IPO/ArgumentPromotion.cpp
+++ lib/Transforms/IPO/ArgumentPromotion.cpp
@@ -156,6 +156,12 @@
       isSelfRecursive = true;
   }
   
+  // Don't promote arguments for variadic functions. Adding, removing, or
+  // changing non-pack parameters can change the classification of pack
+  // parameters. The classification of arguments in the callee is determined
+  // dynamically by clang's expansion of va_arg.
+  if (F->isVarArg()) return nullptr;
+
   // Check to see which arguments are promotable.  If an argument is promotable,
   // add it to ArgsToPromote.
   SmallPtrSet<Argument*, 8> ArgsToPromote;
Index: test/Transforms/ArgumentPromotion/variadic.ll
===================================================================
--- test/Transforms/ArgumentPromotion/variadic.ll
+++ test/Transforms/ArgumentPromotion/variadic.ll
@@ -0,0 +1,23 @@
+; RUN: opt < %s -argpromotion -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.tt0 = type { i64, i64 }
+%struct.__va_list_tag = type { i32, i32, i8*, i8* }
+
+@t45 = internal global %struct.tt0 { i64 1335139741, i64 438042995 }, align 8
+
+; Function Attrs: nounwind uwtable
+define i32 @main(i32 %argc, i8** nocapture readnone %argv) #0 {
+entry:
+  tail call void (i8*, i8*, i8*, i8*, i8*, ...)* @callee_t0f(i8* undef, i8* undef, i8* undef, i8* undef, i8* undef, %struct.tt0* byval align 8 @t45)
+  ret i32 0
+}
+
+; Function Attrs: nounwind uwtable
+; CHECK-NOT: callee_t0f(...)
+define internal void @callee_t0f(i8* nocapture readnone %tp13, i8* nocapture readnone %tp14, i8* nocapture readnone %tp15, i8* nocapture readnone %tp16, i8* nocapture readnone %tp17, ...) {
+entry:
+  ret void
+}
\ No newline at end of file