Index: llvm/trunk/lib/IR/Value.cpp
===================================================================
--- llvm/trunk/lib/IR/Value.cpp
+++ llvm/trunk/lib/IR/Value.cpp
@@ -627,9 +627,9 @@
   CanBeNull = false;
   if (const Argument *A = dyn_cast<Argument>(this)) {
     DerefBytes = A->getDereferenceableBytes();
-    if (DerefBytes == 0 && A->hasByValAttr() && A->getType()->isSized()) {
-      DerefBytes = DL.getTypeStoreSize(A->getType());
-      CanBeNull = false;
+    if (DerefBytes == 0 && A->hasByValAttr()) {
+      Type *PT = cast<PointerType>(A->getType())->getElementType();
+      DerefBytes = DL.getTypeStoreSize(PT);
     }
     if (DerefBytes == 0) {
       DerefBytes = A->getDereferenceableOrNullBytes();
Index: llvm/trunk/test/Analysis/ValueTracking/memory-dereferenceable.ll
===================================================================
--- llvm/trunk/test/Analysis/ValueTracking/memory-dereferenceable.ll
+++ llvm/trunk/test/Analysis/ValueTracking/memory-dereferenceable.ll
@@ -22,7 +22,9 @@
 ; CHECK-LABEL: 'test'
 define void @test(i32 addrspace(1)* dereferenceable(8) %dparam,
                   i8 addrspace(1)* dereferenceable(32) align 1 %dparam.align1,
-                  i8 addrspace(1)* dereferenceable(32) align 16 %dparam.align16)
+                  i8 addrspace(1)* dereferenceable(32) align 16 %dparam.align16,
+                  i8* byval %i8_byval,
+                  %struct.A* byval %A_byval)
     gc "statepoint-example" {
 ; CHECK: The following are dereferenceable:
 entry:
@@ -111,6 +113,18 @@
     %load15 = load i8, i8 addrspace(1)* %dparam.align1, align 16
     %load16 = load i8, i8 addrspace(1)* %dparam.align16, align 16
 
+    ; Loads from byval arguments
+; CHECK: %i8_byval{{.*}}(aligned)
+    %i8_byval_load = load i8, i8* %i8_byval
+
+; CHECK-NOT: %byval_cast
+    %byval_cast = bitcast i8* %i8_byval to i32*
+    %bad_byval_load = load i32, i32* %byval_cast
+
+; CHECK: %byval_gep{{.*}}(aligned)
+    %byval_gep = getelementptr inbounds %struct.A, %struct.A* %A_byval, i64 0, i32 1, i64 2
+    load i8, i8* %byval_gep
+
     ; Loads from aligned allocas
 ; CHECK: %alloca.align1{{.*}}(unaligned)
 ; CHECK: %alloca.align16{{.*}}(aligned)