Index: llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -756,7 +756,7 @@
   bool runOnFunction() {
     if (!ClStack) return false;
 
-    if (ClRedzoneByvalArgs && Mapping.Offset != kDynamicShadowSentinel)
+    if (ClRedzoneByvalArgs)
       copyArgsPassedByValToAllocas();
 
     // Collect alloca, ret, lifetime instructions etc.
@@ -2546,8 +2546,13 @@
 }
 
 void FunctionStackPoisoner::copyArgsPassedByValToAllocas() {
-  BasicBlock &FirstBB = *F.begin();
-  IRBuilder<> IRB(&FirstBB, FirstBB.getFirstInsertionPt());
+  Instruction *CopyInsertPoint = &F.front().front();
+  if (CopyInsertPoint == ASan.LocalDynamicShadow) {
+    // Insert after the dynamic shadow location is determined
+    CopyInsertPoint = CopyInsertPoint->getNextNode();
+    assert(CopyInsertPoint);
+  }
+  IRBuilder<> IRB(CopyInsertPoint);
   const DataLayout &DL = F.getParent()->getDataLayout();
   for (Argument &Arg : F.args()) {
     if (Arg.hasByValAttr()) {
Index: llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-byval-args.ll
===================================================================
--- llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-byval-args.ll
+++ llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-byval-args.ll
@@ -1,6 +1,6 @@
 ; This check verifies that arguments passed by value get redzones.
 ; RUN: opt < %s -asan -asan-realign-stack=32 -S | FileCheck %s
-; RUN: opt < %s -asan -asan-realign-stack=32 -asan-force-dynamic-shadow -S | FileCheck %s --check-prefixes=CHECK-FDS
+; RUN: opt < %s -asan -asan-realign-stack=32 -asan-force-dynamic-shadow -S | FileCheck %s
 
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
@@ -10,8 +10,6 @@
 
 declare i32 @bar(%struct.A*)
 
-; CHECK-FDS-NOT: {{\.byval}}
-
 ; Test behavior for named argument with explicit alignment.  The memcpy and
 ; alloca alignments should match the explicit alignment of 64.
 define void @foo(%struct.A* byval align 64 %a) sanitize_address {