Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -3339,7 +3339,16 @@
     // for the block. \p First is the position of the first size argument.
     auto CreateArrayForSizeVar = [=](unsigned First) {
       auto *AT = llvm::ArrayType::get(SizeTy, NumArgs - First);
+      // Always insert the alloca in the entry block so it remains static in
+      // the SelectionDAG.
+      BasicBlock *Begin = nullptr;
+      if (Instruction *Entry = CurFn->getEntryBlock().getTerminator()) {
+        Begin = Builder.GetInsertBlock();
+        Builder.SetInsertPoint(Entry);
+      }
       auto *Arr = Builder.CreateAlloca(AT);
+      if (Begin)
+        Builder.SetInsertPoint(Begin);
       llvm::Value *Ptr;
       // Each of the following arguments specifies the size of the corresponding
       // argument passed to the enqueued block.
Index: test/CodeGenOpenCL/enqueue-kernel-non-entry-block.cl
===================================================================
--- /dev/null
+++ test/CodeGenOpenCL/enqueue-kernel-non-entry-block.cl
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 %s -cl-std=CL2.0 -O0 -emit-llvm -o - -triple amdgcn | FileCheck %s --check-prefixes=COMMON,AMDGPU
+// RUN: %clang_cc1 %s -cl-std=CL2.0 -O0 -emit-llvm -o - -triple "spir-unknown-unknown" | FileCheck %s --check-prefixes=COMMON,SPIR32
+// RUN: %clang_cc1 %s -cl-std=CL2.0 -O0 -emit-llvm -o - -triple "spir64-unknown-unknown" | FileCheck %s --check-prefixes=COMMON,SPIR64
+
+typedef struct {int a;} ndrange_t;
+
+kernel void test(int i) {
+// COMMON-LABEL: define {{.*}} void @test
+// COMMON-LABEL: entry:
+// AMDGPU: alloca [1 x i64]
+// SPIR32: alloca [1 x i32]
+// SPIR64: alloca [1 x i64]
+// COMMON-LABEL: if.then:
+// COMMON-NOT: alloca
+// COMMON-LABEL: if.end
+  queue_t default_queue;
+  unsigned flags = 0;
+  ndrange_t ndrange;
+  if (i)
+    enqueue_kernel(default_queue, flags, ndrange, ^(local void *a) { }, 32);
+}