[AMDGPU] Fix PreRARematerialize scheduler pass sinking subreg defs

[vangthao]

Summary

When collecting trivially rematerializable defs, skip any subreg defs. We do not want to sink these.

[rampitec]

I thought we do not rematerialize subreg defs at all?

[vangthao]

In D121874#3389932, @rampitec wrote:

I thought we do not rematerialize subreg defs at all?

I incorrectly assumed when defining a subreg, there would be multiple defs for the other parts of the reg so checking hasOneDef() would be sufficient. However in this case, there was a single def of a subreg undef %23.sub1 without any def for sub0.

[rampitec]

In D121874#3389967, @vangthao wrote:

In D121874#3389932, @rampitec wrote:

I thought we do not rematerialize subreg defs at all?

I incorrectly assumed when defining a subreg, there would be multiple defs for the other parts of the reg so checking hasOneDef() would be sufficient. However in this case, there was a single def of a subreg undef %23.sub1 without any def for sub0.

I would suggest to prohibit rematerialization of subreg defs completely instead.

[vangthao]

Skip all defs containing subregs instead of just undefs.

[rampitec]

In D121874#3390011, @vangthao wrote:

Skip all defs containing subregs instead of just undefs.

Also retitle the change.

llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp

810

I would still pass the subreg here. It will be always 0, but not passing it 'spaghettifies' code.

[vangthao]

Changed title and pass subreg to reMaterialze()

[rampitec]

LGTM

llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp

for (unsigned I = 0, E = MRI.getNumVirtRegs(); I != E; ++I) {
 
     // We are only collecting defs that are live-through or defined in another
     // block and used inside this region. This means that the register must be
     // in the live-in set for this region, else skip this def.
     if (HighRPLiveIns.find(Reg) == HighRPLiveIns.end())
       continue;
 
     MachineInstr *Def = MRI.getOneDef(Reg)->getParent();
-    if (!Def || !isTriviallyReMaterializable(*Def, AA))
+    if (!Def || Def->getOperand(0).getSubReg() != 0 ||
+        !isTriviallyReMaterializable(*Def, AA))
       continue;
 
     MachineInstr *UseI = &*MRI.use_instr_begin(Reg);
     if (Def->getParent() == UseI->getParent())
       continue;
 
     RematerializableInsts.push_back(std::make_pair(Def, UseI));
   }
MachineBasicBlock::iterator InsertPos =
         MachineBasicBlock::iterator(It.second);
     Register Reg = Def->getOperand(0).getReg();
     // Rematerialize MI to its use block. Since we are only rematerializing
     // instructions that do not have any virtual reg uses, we do not need to
     // call LiveRangeEdit::allUsesAvailableAt() and
     // LiveRangeEdit::canRematerializeAt().
     NewLiveIns[Reg] = LaneBitmask::getNone();
     TII->reMaterialize(*InsertPos->getParent(), InsertPos, Reg,
                        Def->getOperand(0).getSubReg(), *Def, *TRI);
     MachineInstr *NewMI = &*(--InsertPos);
     LIS->InsertMachineInstrInMaps(*NewMI);
     LIS->removeInterval(Reg);
     LIS->createAndComputeVirtRegInterval(Reg);
     InsertedMIToOldDef[NewMI] = Def;
 
     // FIXME: Need better way to update RP without re-iterating over region
     RPT.reset(*NonDbgMI, &NewLiveIns);

llvm/test/CodeGen/AMDGPU/machine-scheduler-sink-trivial-remats.mir

; predcessors: %bb.1
     S_NOP 0, implicit %10, implicit %11
     S_NOP 0, implicit %12, implicit %13
     S_NOP 0, implicit %14, implicit %15
     S_NOP 0, implicit %16, implicit %17
     S_NOP 0, implicit %18, implicit %19
     S_NOP 0, implicit %20, implicit %21
     S_ENDPGM 0
 ...
+---
+name:            test_occ_9_no_sink_one_def_of_undef_subreg
+tracksRegLiveness: true
+machineFunctionInfo:
+  isEntryFunction: true
+body:             |
+  ; GFX908-LABEL: name: test_occ_9_no_sink_one_def_of_undef_subreg
+  ; GFX908: bb.0:
+  ; GFX908-NEXT:   successors: %bb.1(0x80000000)
+  ; GFX908-NEXT: {{  $}}
+  ; GFX908-NEXT:   %0:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 0, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %1:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 1, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %2:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 2, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %3:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 3, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %4:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 4, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %5:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 5, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %6:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 6, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %7:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 7, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %8:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 8, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %9:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 9, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %10:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 10, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %11:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 11, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %12:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 12, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %13:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 13, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %14:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 14, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %15:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 15, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %16:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 16, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %17:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 17, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %18:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 18, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %19:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 19, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %20:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 20, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %21:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 21, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   %22:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 22, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   undef %23.sub1:vreg_64_align2 = V_MOV_B32_e32 23, implicit $exec
+  ; GFX908-NEXT: {{  $}}
+  ; GFX908-NEXT: bb.1:
+  ; GFX908-NEXT:   successors: %bb.2(0x80000000)
+  ; GFX908-NEXT: {{  $}}
+  ; GFX908-NEXT:   %24:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 24, implicit $exec, implicit $mode, implicit-def $m0
+  ; GFX908-NEXT:   S_NOP 0, implicit %24
+  ; GFX908-NEXT: {{  $}}
+  ; GFX908-NEXT: bb.2:
+  ; GFX908-NEXT:   S_NOP 0, implicit %23.sub1
+  ; GFX908-NEXT:   S_NOP 0, implicit %0, implicit %1
+  ; GFX908-NEXT:   S_NOP 0, implicit %2, implicit %3
+  ; GFX908-NEXT:   S_NOP 0, implicit %4, implicit %5
+  ; GFX908-NEXT:   S_NOP 0, implicit %6, implicit %7
+  ; GFX908-NEXT:   S_NOP 0, implicit %8, implicit %9
+  ; GFX908-NEXT:   S_NOP 0, implicit %10, implicit %11
+  ; GFX908-NEXT:   S_NOP 0, implicit %12, implicit %13
+  ; GFX908-NEXT:   S_NOP 0, implicit %14, implicit %15
+  ; GFX908-NEXT:   S_NOP 0, implicit %16, implicit %17
+  ; GFX908-NEXT:   S_NOP 0, implicit %18, implicit %19
+  ; GFX908-NEXT:   S_NOP 0, implicit %20, implicit %21
+  ; GFX908-NEXT:   S_NOP 0, implicit %22
+  ; GFX908-NEXT:   S_ENDPGM 0
+  bb.0:
+    successors: %bb.1
+
+    %0:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 0, implicit $exec, implicit $mode, implicit-def $m0
+    %1:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 1, implicit $exec, implicit $mode, implicit-def $m0
+    %2:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 2, implicit $exec, implicit $mode, implicit-def $m0
+    %3:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 3, implicit $exec, implicit $mode, implicit-def $m0
+    %4:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 4, implicit $exec, implicit $mode, implicit-def $m0
+    %5:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 5, implicit $exec, implicit $mode, implicit-def $m0
+    %6:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 6, implicit $exec, implicit $mode, implicit-def $m0
+    %7:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 7, implicit $exec, implicit $mode, implicit-def $m0
+    %8:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 8, implicit $exec, implicit $mode, implicit-def $m0
+    %9:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 9, implicit $exec, implicit $mode, implicit-def $m0
+    %10:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 10, implicit $exec, implicit $mode, implicit-def $m0
+    %11:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 11, implicit $exec, implicit $mode, implicit-def $m0
+    %12:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 12, implicit $exec, implicit $mode, implicit-def $m0
+    %13:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 13, implicit $exec, implicit $mode, implicit-def $m0
+    %14:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 14, implicit $exec, implicit $mode, implicit-def $m0
+    %15:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 15, implicit $exec, implicit $mode, implicit-def $m0
+    %16:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 16, implicit $exec, implicit $mode, implicit-def $m0
+    %17:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 17, implicit $exec, implicit $mode, implicit-def $m0
+    %18:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 18, implicit $exec, implicit $mode, implicit-def $m0
+    %19:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 19, implicit $exec, implicit $mode, implicit-def $m0
+    %20:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 20, implicit $exec, implicit $mode, implicit-def $m0
+    %21:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 21, implicit $exec, implicit $mode, implicit-def $m0
+    %22:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 22, implicit $exec, implicit $mode, implicit-def $m0
+    undef %23.sub1:vreg_64_align2 = V_MOV_B32_e32 23, implicit $exec
+
+  bb.1:
+  ; predecessors: %bb.0
+    successors: %bb.2
+
+    %24:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 24, implicit $exec, implicit $mode, implicit-def $m0
+    S_NOP 0, implicit %24
+
+  bb.2:
+  ; predcessors: %bb.1
+
+    S_NOP 0, implicit %23.sub1
+    S_NOP 0, implicit %0, implicit %1
+    S_NOP 0, implicit %2, implicit %3
+    S_NOP 0, implicit %4, implicit %5
+    S_NOP 0, implicit %6, implicit %7
+    S_NOP 0, implicit %8, implicit %9
+    S_NOP 0, implicit %10, implicit %11
+    S_NOP 0, implicit %12, implicit %13
+    S_NOP 0, implicit %14, implicit %15
+    S_NOP 0, implicit %16, implicit %17
+    S_NOP 0, implicit %18, implicit %19
+    S_NOP 0, implicit %20, implicit %21
+    S_NOP 0, implicit %22
+    S_ENDPGM 0
+...