AMDGPU: Fix S_BUFFER_LOAD_DWORD_SGPR moveToVALU.

[bnieuwenhuizen]

Summary

It moves the offset to vgpr, but did not handle being called for
any of the other arguments, while LLVM 5 would select
BUFFER_LOAD_DWORD_OFFEN immediately, which does the right thing.

This calls legalizeOperands to fix up the operands after we converted
to a BUFFER_LOAD_DWORD_OFFEN.

[mareko]

Is this supposed to just insert v_readfirstlane for the descriptor? Can you mention that in the comment before calling legalizeOperands? Can you add a test case? Thanks.

[bnieuwenhuizen]

Adjusted the comment and added a testcase.

The testcase did not turn out to be as simple as I'd hoped, mostly
because you need to trick the structurizer into generating a phi
that results in vgprs for the descriptor.

[bnieuwenhuizen]

Would it be possible to commit this for me again?

[mareko]

Pushed, thanks.

lib/Target/AMDGPU/SIInstrInfo.cpp

case AMDGPU::S_BUFFER_LOAD_DWORD_SGPR: {
             VAddr = getNamedOperand(*Add, SrcNames[!i]);
             break;
           }
 
           Offset = 0;
         }
       }
 
+      MachineInstr *NewInstr =
         BuildMI(*MBB, Inst, Inst.getDebugLoc(),
               get(AMDGPU::BUFFER_LOAD_DWORD_OFFEN), VDst)
         .add(*VAddr) // vaddr
         .add(*getNamedOperand(Inst, AMDGPU::OpName::sbase)) // srsrc
         .addImm(0) // soffset
         .addImm(Offset) // offset
         .addImm(getNamedOperand(Inst, AMDGPU::OpName::glc)->getImm())
         .addImm(0) // slc
         .addImm(0) // tfe
-        .setMemRefs(Inst.memoperands_begin(), Inst.memoperands_end());
+        .setMemRefs(Inst.memoperands_begin(), Inst.memoperands_end())
+        .getInstr();
 
       MRI.replaceRegWith(getNamedOperand(Inst, AMDGPU::OpName::sdst)->getReg(),
                          VDst);
       addUsersToMoveToVALUWorklist(VDst, MRI, Worklist);
       Inst.eraseFromParent();
+
+      // Legalize all operands other than the offset.
+      legalizeOperands(*NewInstr);
       continue;
     }
     }
 
     if (NewOpcode == AMDGPU::INSTRUCTION_LIST_END) {
       // We cannot move this instruction to the VALU, so we should try to
       // legalize its operands instead.
       legalizeOperands(Inst);