Index: lib/Target/AMDGPU/SIISelLowering.h
===================================================================
--- lib/Target/AMDGPU/SIISelLowering.h
+++ lib/Target/AMDGPU/SIISelLowering.h
@@ -80,6 +80,8 @@
                           bool MemcpyStrSrc,
                           MachineFunction &MF) const override;
 
+  bool isNoopAddrSpaceCast(unsigned SrcAS, unsigned DestAS) const override;
+
   TargetLoweringBase::LegalizeTypeAction
   getPreferredVectorAction(EVT VT) const override;
 
Index: lib/Target/AMDGPU/SIISelLowering.cpp
===================================================================
--- lib/Target/AMDGPU/SIISelLowering.cpp
+++ lib/Target/AMDGPU/SIISelLowering.cpp
@@ -492,6 +492,17 @@
   return MVT::Other;
 }
 
+static bool isFlatGlobalAddrSpace(unsigned AS) {
+  return AS == AMDGPUAS::GLOBAL_ADDRESS ||
+    AS == AMDGPUAS::FLAT_ADDRESS ||
+    AS == AMDGPUAS::CONSTANT_ADDRESS;
+}
+
+bool SITargetLowering::isNoopAddrSpaceCast(unsigned SrcAS,
+                                           unsigned DestAS) const {
+  return isFlatGlobalAddrSpace(SrcAS) &&  isFlatGlobalAddrSpace(DestAS);
+}
+
 TargetLoweringBase::LegalizeTypeAction
 SITargetLowering::getPreferredVectorAction(EVT VT) const {
   if (VT.getVectorNumElements() != 1 && VT.getScalarType().bitsLE(MVT::i16))
Index: test/CodeGen/AMDGPU/cgp-addressing-modes-flat.ll
===================================================================
--- test/CodeGen/AMDGPU/cgp-addressing-modes-flat.ll
+++ test/CodeGen/AMDGPU/cgp-addressing-modes-flat.ll
@@ -30,3 +30,69 @@
 done:
   ret void
 }
+
+; OPT-LABEL: @test_sink_noop_addrspacecast_flat_to_global_i32(
+; OPT: getelementptr i32, i32 addrspace(4)* %out,
+; OPT-CI-NOT: getelementptr
+; OPT: br i1
+
+; OPT-CI: ptrtoint
+; OPT-CI: add
+; OPT-CI: inttoptr
+; OPT: br label
+
+; GCN-LABEL: {{^}}test_sink_noop_addrspacecast_flat_to_global_i32:
+; CI: buffer_load_dword {{v[0-9]+}}, s{{\[[0-9]+:[0-9]+\]}}, 0 offset:28
+define void @test_sink_noop_addrspacecast_flat_to_global_i32(i32 addrspace(4)* %out, i32 addrspace(4)* %in, i32 %cond) {
+entry:
+  %out.gep = getelementptr i32, i32 addrspace(4)* %out, i64 999999
+  %in.gep = getelementptr i32, i32 addrspace(4)* %in, i64 7
+  %cast = addrspacecast i32 addrspace(4)* %in.gep to i32 addrspace(1)*
+  %tmp0 = icmp eq i32 %cond, 0
+  br i1 %tmp0, label %endif, label %if
+
+if:
+  %tmp1 = load i32, i32 addrspace(1)* %cast
+  br label %endif
+
+endif:
+  %x = phi i32 [ %tmp1, %if ], [ 0, %entry ]
+  store i32 %x, i32 addrspace(4)* %out.gep
+  br label %done
+
+done:
+  ret void
+}
+
+; OPT-LABEL: @test_sink_noop_addrspacecast_flat_to_constant_i32(
+; OPT: getelementptr i32, i32 addrspace(4)* %out,
+; OPT-CI-NOT: getelementptr
+; OPT: br i1
+
+; OPT-CI: ptrtoint
+; OPT-CI: add
+; OPT-CI: inttoptr
+; OPT: br label
+
+; GCN-LABEL: {{^}}test_sink_noop_addrspacecast_flat_to_constant_i32:
+; CI: s_load_dword {{s[0-9]+}}, s{{\[[0-9]+:[0-9]+\]}}, 0xd
+define void @test_sink_noop_addrspacecast_flat_to_constant_i32(i32 addrspace(4)* %out, i32 addrspace(4)* %in, i32 %cond) {
+entry:
+  %out.gep = getelementptr i32, i32 addrspace(4)* %out, i64 999999
+  %in.gep = getelementptr i32, i32 addrspace(4)* %in, i64 7
+  %cast = addrspacecast i32 addrspace(4)* %in.gep to i32 addrspace(2)*
+  %tmp0 = icmp eq i32 %cond, 0
+  br i1 %tmp0, label %endif, label %if
+
+if:
+  %tmp1 = load i32, i32 addrspace(2)* %cast
+  br label %endif
+
+endif:
+  %x = phi i32 [ %tmp1, %if ], [ 0, %entry ]
+  store i32 %x, i32 addrspace(4)* %out.gep
+  br label %done
+
+done:
+  ret void
+}