AMDGPU: Fix selection failure with dead AssertZext

[arsenm]

Summary

Remove the dead AssertZext or else the ValueType operand will
fail to select for some reason.

[nhaehnle]

lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp

1554–1555

I think this should be outside the loop that iterates over It.

Also, is it a problem if all uses of the FI were removed for the current block, but there are uses in other blocks? Perhaps this check should only apply in the case where FI != EffectiveFI?

[arsenm]

It doesn't really matter because all of this code is broken anyway. I'll drop this and merge the testcase into D24328 which removes this whole thing

lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp

for (auto It = EffectiveFI->use_begin(); !It.atEnd(); ) {
 
           MachineSDNode *Mov = CurDAG->getMachineNode(AMDGPU::V_MOV_B32_e32,
                                                       SDLoc(M), MVT::i32, FI);
           NewOps[Op] = SDValue(Mov, 0);
         }
 
         CurDAG->UpdateNodeOperands(M, makeArrayRef(NewOps, OpN));
       }
+
+      if (EffectiveFI->use_empty())
+        CurDAG->RemoveDeadNode(EffectiveFI.getNode());
     }
   }
 }
 
 void AMDGPUDAGToDAGISel::PostprocessISelDAG() {
   const AMDGPUTargetLowering& Lowering =
     *static_cast<const AMDGPUTargetLowering*>(getTargetLowering());
   bool IsModified = false;

test/CodeGen/AMDGPU/captured-frame-index.ll

define void @stored_fi_to_global_huge_frame_offset(i32* addrspace(1)* %ptr) #0 {
   store volatile i32 0, i32* %gep0.tmp0
   %gep1.tmp0 = getelementptr [4096 x i32], [4096 x i32]* %tmp0, i32 0, i32 4095
   store volatile i32 999, i32* %gep1.tmp0
   %gep0.tmp1 = getelementptr [4096 x i32], [4096 x i32]* %tmp0, i32 0, i32 14
   store i32* %gep0.tmp1, i32* addrspace(1)* %ptr
   ret void
 }
 
+@g1 = external addrspace(1) global i32*
+
+; This was leaving a dead node around resulting in failing to select
+; on the leftover AssertZext's ValueType operand.
+
+; GCN-LABEL: {{^}}cannot_select_assertzext_valuetype:
+; GCN:  s_add_u32 s{{[0-9]+}}, s{{[0-9]+}}, g1@GOTPCREL+4
+; GCN: v_mov_b32_e32 [[FI:v[0-9]+]], 0{{$}}
+; GCN: buffer_store_dword [[FI]]
+define void @cannot_select_assertzext_valuetype(i32 addrspace(1)* %out, i32 %idx) #0 {
+entry:
+  %b = alloca i32, align 4
+  %tmp1 = load volatile i32*, i32* addrspace(1)* @g1, align 4
+  %arrayidx = getelementptr inbounds i32, i32* %tmp1, i32 %idx
+  %tmp2 = load i32, i32* %arrayidx, align 4
+  store volatile i32* %b, i32* addrspace(1)* undef
+  ret void
+}
+
 attributes #0 = { nounwind }