Index: lib/Target/R600/SIISelLowering.h
===================================================================
--- lib/Target/R600/SIISelLowering.h
+++ lib/Target/R600/SIISelLowering.h
@@ -59,6 +59,10 @@
 
 public:
   SITargetLowering(TargetMachine &tm);
+
+  bool isLegalAddressingMode(const AddrMode &AM,
+                             Type *Ty) const override;
+
   bool allowsMisalignedMemoryAccesses(EVT VT, unsigned AS,
                                       unsigned Align,
                                       bool *IsFast) const override;
Index: lib/Target/R600/SIISelLowering.cpp
===================================================================
--- lib/Target/R600/SIISelLowering.cpp
+++ lib/Target/R600/SIISelLowering.cpp
@@ -242,6 +242,48 @@
 // TargetLowering queries
 //===----------------------------------------------------------------------===//
 
+// FIXME: This really needs an address space argument. The immediate offset
+// size is different for different sets of memory instruction sets.
+
+// The single offset DS instructions have a 16-bit unsigned byte offset.
+//
+// MUBUF / MTBUF have a 12-bit unsigned byte offset, and additionally can do
+// r + r + i with addr64. 32-bit has more addressing mode options.
+//
+// SMRD instructions have an 8-bit, dword offset.
+//
+bool SITargetLowering::isLegalAddressingMode(const AddrMode &AM,
+                                             Type *Ty) const {
+  // No global is ever allowed as a base.
+  if (AM.BaseGV)
+    return false;
+
+  // Allow a 16-bit unsigned immediate field, since this is what DS instructions
+  // use.
+  if (!isUInt<16>(AM.BaseOffs))
+    return false;
+
+  // Only support r+r,
+  switch (AM.Scale) {
+  case 0:  // "r+i" or just "i", depending on HasBaseReg.
+    break;
+  case 1:
+    if (AM.HasBaseReg && AM.BaseOffs)  // "r+r+i" is not allowed.
+      return false;
+    // Otherwise we have r+r or r+i.
+    break;
+  case 2:
+    if (AM.HasBaseReg || AM.BaseOffs)  // 2*r+r  or  2*r+i is not allowed.
+      return false;
+    // Allow 2*r as r+r.
+    break;
+  default: // Don't allow n * r
+    return false;
+  }
+
+  return true;
+}
+
 bool SITargetLowering::allowsMisalignedMemoryAccesses(EVT  VT,
                                                       unsigned AddrSpace,
                                                       unsigned Align,
Index: test/CodeGen/R600/ds-negative-offset-addressing-mode-loop.ll
===================================================================
--- /dev/null
+++ test/CodeGen/R600/ds-negative-offset-addressing-mode-loop.ll
@@ -0,0 +1,60 @@
+; RUN: llc -march=r600 -mcpu=SI -verify-machineinstrs < %s | FileCheck -check-prefix=SI %s
+
+declare i32 @llvm.r600.read.tidig.x() #0
+declare void @llvm.AMDGPU.barrier.local() #1
+
+; Function Attrs: nounwind
+; SI-LABEL: @signed_ds_offset_addressing_loop
+; SI: BB0_1:
+; SI: V_ADD_I32_e32 [[VADDR:v[0-9]+]],
+; SI-DAG: DS_READ_B32 v{{[0-9]+}}, [[VADDR]], 0x0
+; SI-DAG: DS_READ_B32 v{{[0-9]+}}, [[VADDR]], 0x4
+; SI-DAG: DS_READ_B32 v{{[0-9]+}}, [[VADDR]], 0x80
+; SI-DAG: DS_READ_B32 v{{[0-9]+}}, [[VADDR]], 0x84
+; SI-DAG: DS_READ_B32 v{{[0-9]+}}, [[VADDR]], 0x100
+; SI: S_ENDPGM
+define void @signed_ds_offset_addressing_loop(float addrspace(1)* noalias nocapture %out, float addrspace(3)* noalias nocapture readonly %lptr, i32 %n) #2 {
+entry:
+  %x.i = tail call i32 @llvm.r600.read.tidig.x() #0
+  %mul = shl nsw i32 %x.i, 1
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %sum.03 = phi float [ 0.000000e+00, %entry ], [ %add13, %for.body ]
+  %offset.02 = phi i32 [ %mul, %entry ], [ %add14, %for.body ]
+  %k.01 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  tail call void @llvm.AMDGPU.barrier.local() #1
+  %arrayidx = getelementptr inbounds float addrspace(3)* %lptr, i32 %offset.02
+  %tmp = load float addrspace(3)* %arrayidx, align 4
+  %add1 = add nsw i32 %offset.02, 1
+  %arrayidx2 = getelementptr inbounds float addrspace(3)* %lptr, i32 %add1
+  %tmp1 = load float addrspace(3)* %arrayidx2, align 4
+  %add3 = add nsw i32 %offset.02, 32
+  %arrayidx4 = getelementptr inbounds float addrspace(3)* %lptr, i32 %add3
+  %tmp2 = load float addrspace(3)* %arrayidx4, align 4
+  %add5 = add nsw i32 %offset.02, 33
+  %arrayidx6 = getelementptr inbounds float addrspace(3)* %lptr, i32 %add5
+  %tmp3 = load float addrspace(3)* %arrayidx6, align 4
+  %add7 = add nsw i32 %offset.02, 64
+  %arrayidx8 = getelementptr inbounds float addrspace(3)* %lptr, i32 %add7
+  %tmp4 = load float addrspace(3)* %arrayidx8, align 4
+  %add9 = fadd float %tmp, %tmp1
+  %add10 = fadd float %add9, %tmp2
+  %add11 = fadd float %add10, %tmp3
+  %add12 = fadd float %add11, %tmp4
+  %add13 = fadd float %sum.03, %add12
+  %inc = add nsw i32 %k.01, 1
+  %add14 = add nsw i32 %offset.02, 97
+  %exitcond = icmp eq i32 %inc, 8
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  %tmp5 = sext i32 %x.i to i64
+  %arrayidx15 = getelementptr inbounds float addrspace(1)* %out, i64 %tmp5
+  store float %add13, float addrspace(1)* %arrayidx15, align 4
+  ret void
+}
+
+attributes #0 = { nounwind readnone }
+attributes #1 = { noduplicate nounwind }
+attributes #2 = { nounwind "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }