[AMDGPU] Fix scheduler live-ins with debug inst at start of block

[vangthao]

Summary

GCNDownwardRPTracker RPTracker.reset() skips debug instructions for NextMI so RPTracker.getNext() will never give the beginning of a sched region if it is a debug value. In this case we will never set the live-ins for that block.

Add check to see if getNext also equals the MI after skipping debug instructions.

[vangthao]

Typo in commit message: "RPTracker.getNext() will *never* give the beginning of a sched region"

[arsenm]

llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp

514

could you just apply skipDebuInstructionsForward to MBB->begin instead of adding a second check

[vangthao]

llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp

514

We would have to call skipDebugInstructionsForward on Regions[CurRegion].first per loop iteration or check if Regions[CurRegion].first is a debug instruction and set region live-ins before the loop.

llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp

void GCNScheduleDAGMILive::computeBlockPressure(const MachineBasicBlock *MBB) {
   size_t CurRegion = RegionIdx;
   for (size_t E = Regions.size(); CurRegion != E; ++CurRegion)
     if (Regions[CurRegion].first->getParent() != MBB)
       break;
   --CurRegion;
 
   auto I = MBB->begin();
   auto LiveInIt = MBBLiveIns.find(MBB);
+  auto &Rgn = Regions[CurRegion];
+  auto *NonDbgMI = &*skipDebugInstructionsForward(Rgn.first, Rgn.second);
   if (LiveInIt != MBBLiveIns.end()) {
     auto LiveIn = std::move(LiveInIt->second);
     RPTracker.reset(*MBB->begin(), &LiveIn);
     MBBLiveIns.erase(LiveInIt);
   } else {
-    auto &Rgn = Regions[CurRegion];
     I = Rgn.first;
-    auto *NonDbgMI = &*skipDebugInstructionsForward(Rgn.first, Rgn.second);
     auto LRS = BBLiveInMap.lookup(NonDbgMI);
 #ifdef EXPENSIVE_CHECKS
     assert(isEqual(getLiveRegsBefore(*NonDbgMI, *LIS), LRS));
 #endif
     RPTracker.reset(*I, &LRS);
   }
 
   for ( ; ; ) {
     I = RPTracker.getNext();
 
-    if (Regions[CurRegion].first == I) {
+    if (Regions[CurRegion].first == I || NonDbgMI == I) {
       LiveIns[CurRegion] = RPTracker.getLiveRegs();
       RPTracker.clearMaxPressure();
     }
 
     if (Regions[CurRegion].second == I) {
       Pressure[CurRegion] = RPTracker.moveMaxPressure();
       if (CurRegion-- == RegionIdx)
         break;

llvm/test/CodeGen/AMDGPU/debug-value-scheduler-liveins.mir

+# RUN: llc -march=amdgcn -mcpu=gfx908 -run-pass=machine-scheduler %s -o - -debug-only=machine-scheduler 2>&1 | FileCheck %s
+# REQUIRES: asserts
+
+# CHECK: ********** MI Scheduling **********
+# CHECK-NEXT: test_get_liveins:%bb.1
+# CHECK: Region live-in pressure:  VGPRs: 1 AGPRs: 0, SGPRs: 0, LVGPR WT: 0, LSGPR WT: 0
+# CHECK: ScheduleDAGMILive::schedule starting
+
+---
+name:            test_get_liveins
+tracksRegLiveness: true
+frameInfo:
+  hasCalls:        true
+body:             |
+  bb.0:
+    successors: %bb.1
+
+    %0:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 0, implicit $exec, implicit $mode, implicit-def $m0
+
+  bb.1:
+    successors: %bb.2
+
+    DBG_VALUE %0:vgpr_32, 0, 0
+    %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
+    %23:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 23, implicit $exec, implicit $mode, implicit-def $m0
+    %24:vgpr_32 = nofpexcept V_CVT_I32_F64_e32 24, implicit $exec, implicit $mode, implicit-def $m0
+
+  bb.2:
+    DBG_VALUE %24:vgpr_32, 0, 0
+    S_NOP 0, implicit %0
+    S_NOP 0, implicit %1, implicit %2
+    S_NOP 0, implicit %3, implicit %4
+    S_NOP 0, implicit %5, implicit %6
+    S_NOP 0, implicit %7, implicit %8
+    S_NOP 0, implicit %9, implicit %10
+    S_NOP 0, implicit %11, implicit %12
+    S_NOP 0, implicit %13, implicit %14
+    S_NOP 0, implicit %15, implicit %16
+    S_NOP 0, implicit %17, implicit %18
+    S_NOP 0, implicit %19, implicit %20
+    S_NOP 0, implicit %21, implicit %22
+    S_NOP 0, implicit %23, implicit %23
+    S_NOP 0, implicit %24
+    S_ENDPGM 0
+...
+