[AMDGPU] Support arbitrary types in amdgcn.dead (#134841)

Legalize the amdgcn.dead intrinsic to work with types other than i32. It
still generates IMPLICIT_DEFs.

Remove some of the previous code for selecting/reg bank mapping it for
32-bit types, since everything is done in the legalizer now.

Author: rovka

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

@@ -1191,12 +1191,6 @@ bool AMDGPUInstructionSelector::selectG_INTRINSIC(MachineInstr &I) const {
   case Intrinsic::amdgcn_permlane16_swap:
   case Intrinsic::amdgcn_permlane32_swap:
     return selectPermlaneSwapIntrin(I, IntrinsicID);
-  case Intrinsic::amdgcn_dead: {
-    I.setDesc(TII.get(TargetOpcode::IMPLICIT_DEF));
-    I.removeOperand(1); // drop intrinsic ID
-    return RBI.constrainGenericRegister(I.getOperand(0).getReg(),
-                                        AMDGPU::VGPR_32RegClass, *MRI);
-  }
   default:
     return selectImpl(I, *CoverageInfo);
   }

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.cpp

@@ -7658,6 +7658,13 @@ bool AMDGPULegalizerInfo::legalizeIntrinsic(LegalizerHelper &Helper,
     return legalizeLaneOp(Helper, MI, IntrID);
   case Intrinsic::amdgcn_s_buffer_prefetch_data:
     return legalizeSBufferPrefetch(Helper, MI);
+  case Intrinsic::amdgcn_dead: {
+    // TODO: Use poison instead of undef
+    for (const MachineOperand &Def : MI.defs())
+      B.buildUndef(Def);
+    MI.eraseFromParent();
+    return true;
+  }
   default: {
     if (const AMDGPU::ImageDimIntrinsicInfo *ImageDimIntr =
             AMDGPU::getImageDimIntrinsicInfo(IntrID))

llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp

@@ -4698,7 +4698,6 @@ AMDGPURegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
     case Intrinsic::amdgcn_set_inactive_chain_arg:
     case Intrinsic::amdgcn_permlane64:
     case Intrinsic::amdgcn_ds_bpermute_fi_b32:
-    case Intrinsic::amdgcn_dead:
       return getDefaultMappingAllVGPR(MI);
     case Intrinsic::amdgcn_cvt_pkrtz:
       if (Subtarget.hasSALUFloatInsts() && isSALUMapping(MI))

llvm/lib/Target/AMDGPU/SIISelLowering.cpp

@@ -6628,6 +6628,11 @@ void SITargetLowering::ReplaceNodeResults(SDNode *N,
       Results.push_back(LoadVal);
       return;
     }
+    case Intrinsic::amdgcn_dead: {
+      for (unsigned I = 0, E = N->getNumValues(); I < E; ++I)
+        Results.push_back(DAG.getPOISON(N->getValueType(I)));
+      return;
+    }
     }
     break;
   }
@@ -9113,6 +9118,12 @@ SDValue SITargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
   case Intrinsic::amdgcn_mov_dpp8:
   case Intrinsic::amdgcn_update_dpp:
     return lowerLaneOp(*this, Op.getNode(), DAG);
+  case Intrinsic::amdgcn_dead: {
+    SmallVector<SDValue, 8> Poisons;
+    for (const EVT ValTy : Op.getNode()->values())
+      Poisons.push_back(DAG.getPOISON(ValTy));
+    return DAG.getMergeValues(Poisons, SDLoc(Op));
+  }
   default:
     if (const AMDGPU::ImageDimIntrinsicInfo *ImageDimIntr =
             AMDGPU::getImageDimIntrinsicInfo(IntrinsicID))

llvm/lib/Target/AMDGPU/SIInstructions.td

@@ -4510,9 +4510,3 @@ def V_ILLEGAL : Enc32, InstSI<(outs), (ins), "v_illegal"> {
   let hasSideEffects = 1;
   let SubtargetPredicate = isGFX10Plus;
 }
-
-// FIXME: Would be nice if we could set the register class for the destination
-// register too.
-def IMP_DEF_FROM_INTRINSIC: Pat<
-  (i32 (int_amdgcn_dead)), (IMPLICIT_DEF)>;
-

llvm/test/CodeGen/AMDGPU/legalize-amdgcn.dead.mir

@@ -0,0 +1,32 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=amdgcn-amdpal -mcpu=gfx1200 -run-pass=legalizer %s -o - | FileCheck %s
+
+---
+name: test_struct
+body: |
+  bb.1.entry:
+
+    ; CHECK-LABEL: name: test_struct
+    ; CHECK: [[DEF:%[0-9]+]]:_(s32) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[DEF1:%[0-9]+]]:_(<3 x s32>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[DEF2:%[0-9]+]]:_(s64) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[DEF3:%[0-9]+]]:_(<2 x s16>) = G_IMPLICIT_DEF
+    ; CHECK-NEXT: [[UV:%[0-9]+]]:_(s32), [[UV1:%[0-9]+]]:_(s32), [[UV2:%[0-9]+]]:_(s32) = G_UNMERGE_VALUES [[DEF1]](<3 x s32>)
+    ; CHECK-NEXT: $vgpr0 = COPY [[DEF]](s32)
+    ; CHECK-NEXT: $vgpr1 = COPY [[UV]](s32)
+    ; CHECK-NEXT: $vgpr2 = COPY [[UV1]](s32)
+    ; CHECK-NEXT: $vgpr3 = COPY [[UV2]](s32)
+    ; CHECK-NEXT: $vgpr4_vgpr5 = COPY [[DEF2]](s64)
+    ; CHECK-NEXT: $vgpr6 = COPY [[DEF3]](<2 x s16>)
+    ; CHECK-NEXT: SI_RETURN implicit $vgpr0, implicit $vgpr1, implicit $vgpr2, implicit $vgpr3, implicit $vgpr4, implicit $vgpr5, implicit $vgpr6, implicit $vgpr7
+    %0:_(s32), %1:_(<3 x s32>), %2:_(s64), %3:_(<2 x s16>) = G_INTRINSIC intrinsic(@llvm.amdgcn.dead)
+
+    %4:_(s32), %5:_(s32), %6:_(s32) = G_UNMERGE_VALUES %1(<3 x s32>)
+    $vgpr0 = COPY %0(s32)
+    $vgpr1 = COPY %4(s32)
+    $vgpr2 = COPY %5(s32)
+    $vgpr3 = COPY %6(s32)
+    $vgpr4_vgpr5 = COPY %2(s64)
+    $vgpr6 = COPY %3(<2 x s16>)
+    SI_RETURN implicit $vgpr0, implicit $vgpr1, implicit $vgpr2, implicit $vgpr3, implicit $vgpr4, implicit $vgpr5, implicit $vgpr6, implicit $vgpr7
+...