Index: lib/Transforms/IPO/ArgumentPromotion.cpp
===================================================================
--- lib/Transforms/IPO/ArgumentPromotion.cpp
+++ lib/Transforms/IPO/ArgumentPromotion.cpp
@@ -183,10 +183,12 @@
           continue;
         }
         
-        // If all the elements are single-value types, we can promote it.
+        // If all the elements are single-value types, we can promote it, unless
+        // its alloca size differs from its size in bits
         bool AllSimple = true;
         for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
-          if (!STy->getElementType(i)->isSingleValueType()) {
+          Type *ElTy = STy->getElementType(i);
+          if (!ElTy->isSingleValueType() || ElTy->isX86_FP80Ty()) {
             AllSimple = false;
             break;
           }
Index: test/Transforms/ArgumentPromotion/fp80.ll
===================================================================
--- test/Transforms/ArgumentPromotion/fp80.ll
+++ test/Transforms/ArgumentPromotion/fp80.ll
@@ -0,0 +1,45 @@
+; 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"
+
+%union.u = type { x86_fp80 }
+
+@b = internal global { { double, i16, i8, [5 x i8] } } { { double, i16, i8, [5 x i8] } { double 3.14, i16 9439, i8 25, [5 x i8] undef } }, align 16
+
+%struct.Foo = type { i32, i64 }
+@a = internal global %struct.Foo { i32 1, i64 2 }, align 8
+
+; Function Attrs: nounwind uwtable
+define i32 @main(i32 %argc, i8** nocapture readnone %argv) {
+entry:
+  tail call fastcc i8 @foo(%union.u* byval align 16 bitcast ({ { double, i16, i8, [5 x i8] } }* @b to %union.u*))
+  tail call fastcc x86_fp80 @baz(%union.u* byval align 16 bitcast ({ { double, i16, i8, [5 x i8] } }* @b to %union.u*))
+  call i64 @qux(%struct.Foo* @a)
+  ret i32 0
+}
+
+; CHECK: @foo(%union.u* byval
+; Function Attrs: noinline nounwind uwtable
+define internal fastcc i8 @foo(%union.u* byval nocapture readonly align 16 %arg) {
+entry:
+  %bitcast = bitcast %union.u* %arg to { double, i16, i8, [5 x i8] }*
+  %gep = getelementptr inbounds { double, i16, i8, [5 x i8] }* %bitcast, i64 0, i32 2
+  %result = load i8* %gep
+  ret i8 %result
+}
+
+; CHECK: @baz(x86_fp80
+; Function Attrs: noinline nounwind uwtable
+define internal fastcc x86_fp80 @baz(%union.u* byval nocapture readonly align 16 %arg) {
+  %gep = getelementptr inbounds %union.u* %arg, i64 0, i32 0
+  %fp80 = load x86_fp80* %gep
+  ret x86_fp80 %fp80
+}
+
+; CHECK: @qux(i32 {{.*}} i64
+define internal i64 @qux(%struct.Foo* byval %a) {
+  %p = bitcast %struct.Foo* %a to i64*
+  %v = load i64* %p
+  ret i64 %v
+}