[AMDGPU] Fix deleting of move-immediate instructions after folding

[foad]

Summary

SIInstrInfo::FoldImmediate tried to delete move-immediate instructions
after folding them into their only use. This did not work because it was
checking hasOneNonDBGUse after doing the fold, at which point there
should be no uses. This seems to have no effect on codegen, it just
means less stuff for DCE to clean up later.

[arsenm]

Can we maybe drop one of the extra runs of machine dce?

[foad]

In D120815#3354418, @arsenm wrote:

Can we maybe drop one of the extra runs of machine dce?

Machine DCE is run right after Peephole Optimizer, but that's done in generic code (TargetPassConfig::addMachineSSAOptimization). I don't see how this would affect any of the other runs of Machine DCE, that are added by the AMDGPU backend.

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

if (Src0->isReg() && Src0->getReg() == Reg) {
         UseMI.untieRegOperand(
             AMDGPU::getNamedOperandIdx(Opc, AMDGPU::OpName::src2));
 
       Src1->ChangeToImmediate(Imm);
 
       removeModOperands(UseMI);
       UseMI.setDesc(get(NewOpc));
 
-      bool DeleteDef = MRI->hasOneNonDBGUse(Reg);
+      bool DeleteDef = MRI->use_nodbg_empty(Reg);
       if (DeleteDef)
         DefMI.eraseFromParent();
 
       return true;
     }
 
     // Added part is the constant: Use v_madak_{f16, f32}.
     if (Src2->isReg() && Src2->getReg() == Reg) {
if (Src2->isReg() && Src2->getReg() == Reg) {
       // These come before src2.
       removeModOperands(UseMI);
       UseMI.setDesc(get(NewOpc));
       // It might happen that UseMI was commuted
       // and we now have SGPR as SRC1. If so 2 inlined
       // constant and SGPR are illegal.
       legalizeOperands(UseMI);
 
-      bool DeleteDef = MRI->hasOneNonDBGUse(Reg);
+      bool DeleteDef = MRI->use_nodbg_empty(Reg);
       if (DeleteDef)
         DefMI.eraseFromParent();
 
       return true;
     }
   }
 
   return false;

llvm/test/CodeGen/AMDGPU/madak-inline-constant.mir

 # RUN: llc -march=amdgcn -run-pass peephole-opt -verify-machineinstrs -o - %s | FileCheck -check-prefix=GCN %s
 
 
 # GCN-LABEL: bb.0:
-# GCN:  V_MOV_B32_e32 1092616192
 # GCN:  S_MOV_B32 1082130432
 # GCN:  %3:vgpr_32 = V_MADAK_F32 1082130432, killed %0, 1092616192, implicit $mode, implicit $exec
 
 ---
 name:            test src1-inlined
 body:             |
   bb.0:
     liveins: $vgpr0, $sgpr0_sgpr1
 
     %0:vgpr_32 = COPY $vgpr0
     %17:vgpr_32 = V_MOV_B32_e32 1092616192, implicit $exec
     %18:sreg_32 = S_MOV_B32 1082130432
     %19:vgpr_32 = V_MAC_F32_e64 0, killed %0, 0, killed %18, 0, %17, 0, 0, implicit $mode, implicit $exec
 
 ...
 
 
 # GCN-LABEL: bb.0:
-# GCN:  V_MOV_B32_e32 1092616192
 # GCN:  S_MOV_B32 1082130432
 # GCN:  %3:vgpr_32 = V_MADAK_F32 1082130432, killed %0, 1092616192, implicit $mode, implicit $exec
 
 ---
 name:            test src0-inlined
 body:             |
   bb.0:
     liveins: $vgpr0, $sgpr0_sgpr1
 
     %0:vgpr_32 = COPY $vgpr0
     %17:vgpr_32 = V_MOV_B32_e32 1092616192, implicit $exec
     %18:sreg_32 = S_MOV_B32 1082130432
     %19:vgpr_32 = V_MAC_F32_e64 0, killed %18, 0, killed %0, 0, %17, 0, 0, implicit $mode, implicit $exec
 
 ...
 
 # GCN-LABEL: bb.0:
-# GCN:  V_MOV_B32_e32 1092616192
 # GCN:  S_MOV_B32 1082130432
 # GCN:  %3:vgpr_32 = V_MADAK_F32 killed %0, killed %0, 1092616192, implicit $mode, implicit $exec
 
 ---
 name:            test none-inlined
 body:             |
   bb.0:
     liveins: $vgpr0, $sgpr0_sgpr1
 
     %0:vgpr_32 = COPY $vgpr0
     %17:vgpr_32 = V_MOV_B32_e32 1092616192, implicit $exec
     %18:sreg_32 = S_MOV_B32 1082130432
     %19:vgpr_32 = V_MAC_F32_e64 0, killed %0, 0, killed %0, 0, %17, 0, 0, implicit $mode, implicit $exec
 
 ...
 
 # GCN-LABEL: bb.0:
-# GCN:  V_MOV_B32_e32 1092616192
 # GCN:  V_MOV_B32_e32 1082130432
 # GCN:  %3:vgpr_32 = V_MADAK_F32 1082130432, killed %0, 1092616192, implicit $mode, implicit $exec
 
 ---
 name:            test src1-2vgprs-inlined
 body:             |
   bb.0:
     liveins: $vgpr0, $sgpr0_sgpr1
 
     %0:vgpr_32 = COPY $vgpr0
     %17:vgpr_32 = V_MOV_B32_e32 1092616192, implicit $exec
     %18:vgpr_32 = V_MOV_B32_e32 1082130432, implicit $exec
     %19:vgpr_32 = V_MAC_F32_e64 0, killed %0, 0, killed %18, 0, %17, 0, 0, implicit $mode, implicit $exec
 
 ...
 
 
 # GCN-LABEL: bb.0:
-# GCN:  V_MOV_B32_e32 1092616192
 # GCN:  V_MOV_B32_e32 1082130432
 # GCN:  %3:vgpr_32 = V_MADAK_F32 1082130432, killed %0, 1092616192, implicit $mode, implicit $exec
 
 ---
 name:            test src0-2vgprs-inlined
 body:             |
   bb.0:
     liveins: $vgpr0, $sgpr0_sgpr1
 
     %0:vgpr_32 = COPY $vgpr0
     %17:vgpr_32 = V_MOV_B32_e32 1092616192, implicit $exec
     %18:vgpr_32 = V_MOV_B32_e32 1082130432, implicit $exec
     %19:vgpr_32 = V_MAC_F32_e64 0, killed %18, 0, killed %0, 0, %17, 0, 0, implicit $mode, implicit $exec
 
 ...
 
 # GCN-LABEL: bb.0:
-# GCN:  V_MOV_B32_e32 1092616192, implicit $exec
 # GCN:  S_MOV_B32 1082130432
 # GCN:  V_MADAK_F32 1082130432, killed $vgpr1, 1092616192, implicit $mode, implicit $exec
 
 ---
 name:            test src0-phys-vgpr
 body:             |
   bb.0:
     liveins: $vgpr0, $sgpr0_sgpr1
 
 
     $vgpr1 = COPY $vgpr0
     %17:vgpr_32 = V_MOV_B32_e32 1092616192, implicit $exec
     %18:sgpr_32 = S_MOV_B32 1082130432
     %19:vgpr_32 = V_MAC_F32_e64 0, killed $vgpr1, 0, killed %18, 0, %17, 0, 0, implicit $mode, implicit $exec
 
 ...
 
 # GCN-LABEL: bb.0:
-# GCN:  V_MOV_B32_e32 1092616192, implicit $exec
 # GCN:  S_MOV_B32 1082130432
 # GCN:  V_MADAK_F32 1082130432, killed $vgpr0, 1092616192, implicit $mode, implicit $exec
 
 ---
 name:            test src1-phys-vgpr
 body:             |
   bb.0:
     liveins: $vgpr0, $sgpr0_sgpr1
bb.0:
 
     %0:vgpr_32 = COPY $vgpr0
     %17:vgpr_32 = V_MOV_B32_e32 1092616192, implicit $exec
     %19:vgpr_32 = V_MAC_F32_e64 0, killed %0, 0, killed $sgpr2, 0, %17, 0, 0, implicit $mode, implicit $exec
 
 ...
 
 # GCN-LABEL: bb.0:
-# GCN:  V_MOV_B32_e32 1092616192, implicit $exec
 # GCN:  $sgpr2 = S_MOV_B32 1082130432
 # GCN:  V_MADAK_F32 1082130432, killed %0, 1092616192, implicit $mode, implicit $exec
 
 ---
 name:            test src1-phys-sgpr-move
 body:             |
   bb.0:
     liveins: $vgpr0, $sgpr0_sgpr1
 
 
     %0:vgpr_32 = COPY $vgpr0
     %17:vgpr_32 = V_MOV_B32_e32 1092616192, implicit $exec
     $sgpr2 = S_MOV_B32 1082130432
     %19:vgpr_32 = V_MAC_F32_e64 0, killed %0, 0, killed $sgpr2, 0, %17, 0, 0, implicit $mode, implicit $exec
 
 ...