Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -10702,6 +10702,17 @@
   if (isConstantFPBuildVectorOrConstantFP(N0))
     return DAG.getNode(ISD::FTRUNC, SDLoc(N), VT, N0);
 
+  // fold ftrunc (known rounded int x) -> x
+  switch (N0.getOpcode()) {
+  default: break;
+  case ISD::FRINT:
+  case ISD::FTRUNC:
+  case ISD::FNEARBYINT:
+  case ISD::FFLOOR:
+  case ISD::FCEIL:
+    return N0;
+  }
+
   return SDValue();
 }
 
Index: test/CodeGen/AMDGPU/combine-ftrunc.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AMDGPU/combine-ftrunc.ll
@@ -0,0 +1,92 @@
+; RUN: llc -march=amdgcn -mcpu=tonga -verify-machineinstrs < %s | FileCheck -check-prefix=GCN %s
+
+; GCN-LABEL: {{^}}combine_ftrunc_frint_f64:
+; GCN: v_rndne_f64_e32 [[RND:v\[[0-9:]+\]]],
+; GCN: flat_store_dwordx2 v[{{[0-9:]+}}], [[RND]]
+define amdgpu_kernel void @combine_ftrunc_frint_f64(double addrspace(1)* %p) {
+  %v = load double, double addrspace(1)* %p, align 8
+  %round = tail call double @llvm.rint.f64(double %v)
+  %trunc = tail call double @llvm.trunc.f64(double %round)
+  store double %trunc, double addrspace(1)* %p, align 8
+  ret void
+}
+
+; GCN-LABEL: {{^}}combine_ftrunc_frint_f32:
+; GCN: v_rndne_f32_e32 [[RND:v[0-9]+]],
+; GCN: flat_store_dword v[{{[0-9:]+}}], [[RND]]
+define amdgpu_kernel void @combine_ftrunc_frint_f32(float addrspace(1)* %p) {
+  %v = load float, float addrspace(1)* %p, align 4
+  %round = tail call float @llvm.rint.f32(float %v)
+  %trunc = tail call float @llvm.trunc.f32(float %round)
+  store float %trunc, float addrspace(1)* %p, align 4
+  ret void
+}
+
+; GCN-LABEL: {{^}}combine_ftrunc_frint_v2f32:
+; GCN: s_load_dwordx2
+; GCN: s_load_dwordx2 s{{\[}}[[SRC1:[0-9]+]]:[[SRC2:[0-9]+]]{{\]}}
+; GCN-DAG: v_rndne_f32_e32 v[[RND1:[0-9]+]], s[[SRC1]]
+; GCN-DAG: v_rndne_f32_e32 v[[RND2:[0-9]+]], s[[SRC2]]
+; GCN: flat_store_dwordx2 v[{{[0-9:]+}}], v{{\[}}[[RND1]]:[[RND2]]{{\]}}
+define amdgpu_kernel void @combine_ftrunc_frint_v2f32(<2 x float> addrspace(1)* %p) {
+  %v = load <2 x float>, <2 x float> addrspace(1)* %p, align 8
+  %round = tail call <2 x float> @llvm.rint.v2f32(<2 x float> %v)
+  %trunc = tail call <2 x float> @llvm.trunc.v2f32(<2 x float> %round)
+  store <2 x float> %trunc, <2 x float> addrspace(1)* %p, align 8
+  ret void
+}
+
+; GCN-LABEL: {{^}}combine_ftrunc_fceil_f32:
+; GCN: v_ceil_f32_e32 [[RND:v[0-9]+]],
+; GCN: flat_store_dword v[{{[0-9:]+}}], [[RND]]
+define amdgpu_kernel void @combine_ftrunc_fceil_f32(float addrspace(1)* %p) {
+  %v = load float, float addrspace(1)* %p, align 4
+  %round = tail call float @llvm.ceil.f32(float %v)
+  %trunc = tail call float @llvm.trunc.f32(float %round)
+  store float %trunc, float addrspace(1)* %p, align 4
+  ret void
+}
+
+; GCN-LABEL: {{^}}combine_ftrunc_ffloor_f32:
+; GCN: v_floor_f32_e32 [[RND:v[0-9]+]],
+; GCN: flat_store_dword v[{{[0-9:]+}}], [[RND]]
+define amdgpu_kernel void @combine_ftrunc_ffloor_f32(float addrspace(1)* %p) {
+  %v = load float, float addrspace(1)* %p, align 4
+  %round = tail call float @llvm.floor.f32(float %v)
+  %trunc = tail call float @llvm.trunc.f32(float %round)
+  store float %trunc, float addrspace(1)* %p, align 4
+  ret void
+}
+
+; GCN-LABEL: {{^}}combine_ftrunc_fnearbyint_f32:
+; GCN: v_rndne_f32_e32 [[RND:v[0-9]+]],
+; GCN: flat_store_dword v[{{[0-9:]+}}], [[RND]]
+define amdgpu_kernel void @combine_ftrunc_fnearbyint_f32(float addrspace(1)* %p) {
+  %v = load float, float addrspace(1)* %p, align 4
+  %round = tail call float @llvm.nearbyint.f32(float %v)
+  %trunc = tail call float @llvm.trunc.f32(float %round)
+  store float %trunc, float addrspace(1)* %p, align 4
+  ret void
+}
+
+; GCN-LABEL: {{^}}combine_ftrunc_ftrunc_f32:
+; GCN: s_load_dword [[SRC:s[0-9]+]],
+; GCN: v_trunc_f32_e32 [[RND:v[0-9]+]], [[SRC]]
+; GCN: flat_store_dword v[{{[0-9:]+}}], [[RND]]
+define amdgpu_kernel void @combine_ftrunc_ftrunc_f32(float addrspace(1)* %p) {
+  %v = load float, float addrspace(1)* %p, align 4
+  %round = tail call float @llvm.trunc.f32(float %v)
+  %trunc = tail call float @llvm.trunc.f32(float %round)
+  store float %trunc, float addrspace(1)* %p, align 4
+  ret void
+}
+
+declare double @llvm.trunc.f64(double)
+declare float @llvm.trunc.f32(float)
+declare <2 x float> @llvm.trunc.v2f32(<2 x float>)
+declare double @llvm.rint.f64(double)
+declare float @llvm.rint.f32(float)
+declare <2 x float> @llvm.rint.v2f32(<2 x float>)
+declare float @llvm.ceil.f32(float)
+declare float @llvm.floor.f32(float)
+declare float @llvm.nearbyint.f32(float)