AMDGPU: Fix assertion on fixed stack objects with VGPR->AGPR spills

[arsenm]

Summary

These have negative / out of bounds frame index values and would
assert when trying to set the BitVector. Fixed stack objects can't be
colored away so ignore them.

[arsenm]

18aabae8e2b6ccea4575ac9e4fb4d38ec7e4e971

llvm/lib/Target/AMDGPU/SIFrameLowering.cpp

for (MachineBasicBlock &MBB : MF) {
             // FIXME: change to enterBasicBlockEnd()
             RS->enterBasicBlock(MBB);
             TRI->eliminateFrameIndex(MI, 0, FIOp, RS);
             SpillFIs.set(FI);
             continue;
           }
         } else if (TII->isStoreToStackSlot(MI, FrameIndex) ||
                    TII->isLoadFromStackSlot(MI, FrameIndex))
+          if (!MFI.isFixedObjectIndex(FrameIndex))
             NonVGPRSpillFIs.set(FrameIndex);
       }
     }
 
     // Stack slot coloring may assign different objets to the same stack slot.
     // If not, then the VGPR to AGPR spill slot is dead.
     for (unsigned FI : SpillFIs.set_bits())
       if (!NonVGPRSpillFIs.test(FI))
         FuncInfo->setVGPRToAGPRSpillDead(FI);

llvm/test/CodeGen/AMDGPU/spill-vgpr-to-agpr.ll

st:
   store volatile <32 x float> %v5, <32 x float> addrspace(1)* undef
   store volatile <32 x float> %v6, <32 x float> addrspace(1)* undef
   store volatile <32 x float> %v7, <32 x float> addrspace(1)* undef
   store volatile <32 x float> %v8, <32 x float> addrspace(1)* undef
   store volatile <32 x float> %v9, <32 x float> addrspace(1)* undef
   ret void
 }
 
+; Make sure there's no crash when we have loads from fixed stack
+; objects and are processing VGPR spills
+
+; GCN-LABEL: {{^}}stack_args_vgpr_spill:
+; GFX908: v_accvgpr_write_b32
+; GFX908: buffer_load_dword v{{[0-9]+}}, off, s[0:3], s32
+; GFX908: buffer_load_dword v{{[0-9]+}}, off, s[0:3], s32 offset:4
+define void @stack_args_vgpr_spill(<32 x float> %arg0, <32 x float> %arg1, <32 x float> addrspace(1)* %p) #1 {
+  %tid = call i32 @llvm.amdgcn.workitem.id.x()
+  %p1 = getelementptr inbounds <32 x float>, <32 x float> addrspace(1)* %p, i32 %tid
+  %p2 = getelementptr inbounds <32 x float>, <32 x float> addrspace(1)* %p1, i32 %tid
+  %p3 = getelementptr inbounds <32 x float>, <32 x float> addrspace(1)* %p2, i32 %tid
+  %p4 = getelementptr inbounds <32 x float>, <32 x float> addrspace(1)* %p3, i32 %tid
+  %p5 = getelementptr inbounds <32 x float>, <32 x float> addrspace(1)* %p4, i32 %tid
+  %p6 = getelementptr inbounds <32 x float>, <32 x float> addrspace(1)* %p5, i32 %tid
+  %p7 = getelementptr inbounds <32 x float>, <32 x float> addrspace(1)* %p6, i32 %tid
+  %v1 = load volatile <32 x float>, <32 x float> addrspace(1)* %p1
+  %v2 = load volatile <32 x float>, <32 x float> addrspace(1)* %p2
+  %v3 = load volatile <32 x float>, <32 x float> addrspace(1)* %p3
+  %v4 = load volatile <32 x float>, <32 x float> addrspace(1)* %p4
+  %v5 = load volatile <32 x float>, <32 x float> addrspace(1)* %p5
+  %v6 = load volatile <32 x float>, <32 x float> addrspace(1)* %p6
+  %v7 = load volatile <32 x float>, <32 x float> addrspace(1)* %p7
+  br label %st
+
+st:
+  store volatile <32 x float> %arg0, <32 x float> addrspace(1)* undef
+  store volatile <32 x float> %arg1, <32 x float> addrspace(1)* undef
+  store volatile <32 x float> %v1, <32 x float> addrspace(1)* undef
+  store volatile <32 x float> %v2, <32 x float> addrspace(1)* undef
+  store volatile <32 x float> %v3, <32 x float> addrspace(1)* undef
+  store volatile <32 x float> %v4, <32 x float> addrspace(1)* undef
+  store volatile <32 x float> %v5, <32 x float> addrspace(1)* undef
+  store volatile <32 x float> %v6, <32 x float> addrspace(1)* undef
+  store volatile <32 x float> %v7, <32 x float> addrspace(1)* undef
+  ret void
+}
+
+
 declare i32 @llvm.amdgcn.workitem.id.x()
 
 attributes #0 = { nounwind "amdgpu-num-vgpr"="10" }
 attributes #1 = { "amdgpu-flat-work-group-size"="1,256" }