AMDGPU/GlobalISel: Implement select() for G_IMPLICIT_DEF

Reviewers: arsenm, nhaehnle

Subscribers: kzhuravl, wdng, yaxunl, rovka, kristof.beyls, dstuttard, tpr, t-tye, llvm-commits

Differential Revision: https://reviews.llvm.org/D46150

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335307 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

@@ -159,6 +159,19 @@ bool AMDGPUInstructionSelector::selectG_GEP(MachineInstr &I) const {
   return selectG_ADD(I);
 }
 
+bool AMDGPUInstructionSelector::selectG_IMPLICIT_DEF(MachineInstr &I) const {
+  MachineBasicBlock *BB = I.getParent();
+  MachineFunction *MF = BB->getParent();
+  MachineRegisterInfo &MRI = MF->getRegInfo();
+  const MachineOperand &MO = I.getOperand(0);
+  const TargetRegisterClass *RC =
+      TRI.getConstrainedRegClassForOperand(MO, MRI);
+  if (RC)
+    RBI.constrainGenericRegister(MO.getReg(), *RC, MRI);
+  I.setDesc(TII.get(TargetOpcode::IMPLICIT_DEF));
+  return true;
+}
+
 bool AMDGPUInstructionSelector::selectG_INTRINSIC(MachineInstr &I,
                                           CodeGenCoverage &CoverageInfo) const {
   unsigned IntrinsicID =  I.getOperand(1).getIntrinsicID();
@@ -535,6 +548,8 @@ bool AMDGPUInstructionSelector::select(MachineInstr &I,
     return selectG_CONSTANT(I);
   case TargetOpcode::G_GEP:
     return selectG_GEP(I);
+  case TargetOpcode::G_IMPLICIT_DEF:
+    return selectG_IMPLICIT_DEF(I);
   case TargetOpcode::G_INTRINSIC:
     return selectG_INTRINSIC(I, CoverageInfo);
   case TargetOpcode::G_LOAD:

lib/Target/AMDGPU/AMDGPUInstructionSelector.h

@@ -63,6 +63,7 @@ private:
   bool selectG_CONSTANT(MachineInstr &I) const;
   bool selectG_ADD(MachineInstr &I) const;
   bool selectG_GEP(MachineInstr &I) const;
+  bool selectG_IMPLICIT_DEF(MachineInstr &I) const;
   bool selectG_INTRINSIC(MachineInstr &I, CodeGenCoverage &CoverageInfo) const;
   bool hasVgprParts(ArrayRef<GEPInfo> AddrInfo) const;
   void getAddrModeInfo(const MachineInstr &Load, const MachineRegisterInfo &MRI,

test/CodeGen/AMDGPU/GlobalISel/inst-select-implicit-def.mir

@@ -0,0 +1,25 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+# RUN: llc -march=amdgcn -run-pass=instruction-select -verify-machineinstrs -global-isel %s -o - | FileCheck %s -check-prefixes=GCN
+
+--- |
+  define amdgpu_kernel void @implicit_def(i32 addrspace(1)* %global0) {ret void}
+...
+---
+
+name:            implicit_def
+legalized:       true
+regBankSelected: true
+
+
+body: |
+  bb.0:
+    liveins: $vgpr3_vgpr4
+    ; GCN-LABEL: name: implicit_def
+    ; GCN: [[COPY:%[0-9]+]]:vreg_64 = COPY $vgpr3_vgpr4
+    ; GCN: [[DEF:%[0-9]+]]:vgpr_32 = IMPLICIT_DEF
+    ; GCN: FLAT_STORE_DWORD [[COPY]], [[DEF]], 0, 0, 0, implicit $exec, implicit $flat_scr
+    %0:vgpr(s64) = COPY $vgpr3_vgpr4
+    %1:vgpr(s32) = G_IMPLICIT_DEF
+    G_STORE %1, %0 :: (store 4 into %ir.global0)
+...
+---