[AMDGPU] New intrinsic llvm.amdgcn.pops.exiting.wave.id (llvm#89612)

This provides access to the special scalar source value
SRC_POPS_EXITING_WAVE_ID on GFX9 and GFX10.

Author: jayfoad

llvm/include/llvm/IR/IntrinsicsAMDGPU.td

@@ -2482,6 +2482,11 @@ class AMDGPUGlobalLoadLDS :
      "", [SDNPMemOperand]>;
 def int_amdgcn_global_load_lds : AMDGPUGlobalLoadLDS;
 
+// Use read/write of inaccessible memory to model the fact that this reads a
+// volatile value.
+def int_amdgcn_pops_exiting_wave_id :
+  DefaultAttrsIntrinsic<[llvm_i32_ty], [], [IntrInaccessibleMemOnly]>;
+
 //===----------------------------------------------------------------------===//
 // GFX10 Intrinsics
 //===----------------------------------------------------------------------===//

llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.cpp

@@ -2526,6 +2526,14 @@ void AMDGPUDAGToDAGISel::SelectDSBvhStackIntrinsic(SDNode *N) {
   CurDAG->setNodeMemRefs(cast<MachineSDNode>(Selected), {MMO});
 }
 
+void AMDGPUDAGToDAGISel::SelectPOPSExitingWaveID(SDNode *N) {
+  // TODO: Select this with a tablegen pattern. This is tricky because the
+  // intrinsic is IntrReadMem/IntrWriteMem but the instruction is not marked
+  // mayLoad/mayStore and tablegen complains about the mismatch.
+  SDValue Reg = CurDAG->getRegister(AMDGPU::SRC_POPS_EXITING_WAVE_ID, MVT::i32);
+  CurDAG->SelectNodeTo(N, AMDGPU::S_MOV_B32, N->getVTList(), Reg);
+}
+
 static unsigned gwsIntrinToOpcode(unsigned IntrID) {
   switch (IntrID) {
   case Intrinsic::amdgcn_ds_gws_init:
@@ -2682,6 +2690,9 @@ void AMDGPUDAGToDAGISel::SelectINTRINSIC_W_CHAIN(SDNode *N) {
   case Intrinsic::amdgcn_ds_bvh_stack_rtn:
     SelectDSBvhStackIntrinsic(N);
     return;
+  case Intrinsic::amdgcn_pops_exiting_wave_id:
+    SelectPOPSExitingWaveID(N);
+    return;
   }
 
   SelectCode(N);

llvm/lib/Target/AMDGPU/AMDGPUISelDAGToDAG.h

@@ -274,6 +274,7 @@ class AMDGPUDAGToDAGISel : public SelectionDAGISel {
   void SelectFP_EXTEND(SDNode *N);
   void SelectDSAppendConsume(SDNode *N, unsigned IntrID);
   void SelectDSBvhStackIntrinsic(SDNode *N);
+  void SelectPOPSExitingWaveID(SDNode *N);
   void SelectDS_GWS(SDNode *N, unsigned IntrID);
   void SelectInterpP1F16(SDNode *N);
   void SelectINTRINSIC_W_CHAIN(SDNode *N);

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

@@ -2079,6 +2079,21 @@ bool AMDGPUInstructionSelector::selectDSBvhStackIntrinsic(
   return constrainSelectedInstRegOperands(*MIB, TII, TRI, RBI);
 }
 
+bool AMDGPUInstructionSelector::selectPOPSExitingWaveID(
+    MachineInstr &MI) const {
+  Register Dst = MI.getOperand(0).getReg();
+  const DebugLoc &DL = MI.getDebugLoc();
+  MachineBasicBlock *MBB = MI.getParent();
+
+  // TODO: Select this with a tablegen pattern. This is tricky because the
+  // intrinsic is IntrReadMem/IntrWriteMem but the instruction is not marked
+  // mayLoad/mayStore and tablegen complains about the mismatch.
+  auto MIB = BuildMI(*MBB, &MI, DL, TII.get(AMDGPU::S_MOV_B32), Dst)
+                 .addDef(AMDGPU::SRC_POPS_EXITING_WAVE_ID);
+  MI.eraseFromParent();
+  return constrainSelectedInstRegOperands(*MIB, TII, TRI, RBI);
+}
+
 bool AMDGPUInstructionSelector::selectG_INTRINSIC_W_SIDE_EFFECTS(
     MachineInstr &I) const {
   unsigned IntrinsicID = cast<GIntrinsic>(I).getIntrinsicID();
@@ -2129,6 +2144,8 @@ bool AMDGPUInstructionSelector::selectG_INTRINSIC_W_SIDE_EFFECTS(
     return selectSBarrierSignalIsfirst(I, IntrinsicID);
   case Intrinsic::amdgcn_s_barrier_leave:
     return selectSBarrierLeave(I);
+  case Intrinsic::amdgcn_pops_exiting_wave_id:
+    return selectPOPSExitingWaveID(I);
   }
   return selectImpl(I, *CoverageInfo);
 }

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.h

@@ -125,6 +125,7 @@ class AMDGPUInstructionSelector final : public InstructionSelector {
   bool selectDSAppendConsume(MachineInstr &MI, bool IsAppend) const;
   bool selectSBarrier(MachineInstr &MI) const;
   bool selectDSBvhStackIntrinsic(MachineInstr &MI) const;
+  bool selectPOPSExitingWaveID(MachineInstr &MI) const;
 
   bool selectImageIntrinsic(MachineInstr &MI,
                             const AMDGPU::ImageDimIntrinsicInfo *Intr) const;

llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp

@@ -5132,6 +5132,8 @@ AMDGPURegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
       OpdsMapping[2] = getSGPROpMapping(MI.getOperand(2).getReg(), MRI, *TRI);
       break;
     }
+    case Intrinsic::amdgcn_pops_exiting_wave_id:
+      return getDefaultMappingSOP(MI);
     default:
       return getInvalidInstructionMapping();
     }

llvm/test/CodeGen/AMDGPU/llvm.amdgcn.pops.exiting.wave.id.ll

@@ -0,0 +1,34 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc -global-isel=0 -mtriple=amdgcn -mcpu=gfx900 < %s | FileCheck %s -check-prefix=SDAG
+; RUN: llc -global-isel=1 -mtriple=amdgcn -mcpu=gfx900 < %s | FileCheck %s -check-prefix=GFX9-GISEL
+; RUN: llc -global-isel=0 -mtriple=amdgcn -mcpu=gfx1010 < %s | FileCheck %s -check-prefix=SDAG
+; RUN: llc -global-isel=1 -mtriple=amdgcn -mcpu=gfx1010 < %s | FileCheck %s -check-prefix=GFX10-GISEL
+
+define amdgpu_ps void @test(ptr addrspace(1) inreg %ptr) {
+; SDAG-LABEL: test:
+; SDAG:       ; %bb.0:
+; SDAG-NEXT:    s_mov_b32 s2, src_pops_exiting_wave_id
+; SDAG-NEXT:    v_mov_b32_e32 v0, 0
+; SDAG-NEXT:    v_mov_b32_e32 v1, s2
+; SDAG-NEXT:    global_store_dword v0, v1, s[0:1]
+; SDAG-NEXT:    s_endpgm
+;
+; GFX9-GISEL-LABEL: test:
+; GFX9-GISEL:       ; %bb.0:
+; GFX9-GISEL-NEXT:    s_mov_b32 s2, src_pops_exiting_wave_id
+; GFX9-GISEL-NEXT:    v_mov_b32_e32 v0, s2
+; GFX9-GISEL-NEXT:    v_mov_b32_e32 v1, 0
+; GFX9-GISEL-NEXT:    global_store_dword v1, v0, s[0:1]
+; GFX9-GISEL-NEXT:    s_endpgm
+;
+; GFX10-GISEL-LABEL: test:
+; GFX10-GISEL:       ; %bb.0:
+; GFX10-GISEL-NEXT:    s_mov_b32 s2, src_pops_exiting_wave_id
+; GFX10-GISEL-NEXT:    v_mov_b32_e32 v1, 0
+; GFX10-GISEL-NEXT:    v_mov_b32_e32 v0, s2
+; GFX10-GISEL-NEXT:    global_store_dword v1, v0, s[0:1]
+; GFX10-GISEL-NEXT:    s_endpgm
+  %id = call i32 @llvm.amdgcn.pops.exiting.wave.id()
+  store i32 %id, ptr addrspace(1) %ptr
+  ret void
+}