[LiveDebugValues] Disable spill tracking on AMDGPU (llvm#775)

Author: jharryma

llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp

@@ -156,6 +156,15 @@ static cl::opt<unsigned>
                          cl::desc("livedebugvalues-stack-ws-limit"),
                          cl::init(250));
 
+// Limit for the maximum number of stack slot indexes. On targets where this is
+// exceeded, this effectivly disables tracking debug locations across spills.
+// The spill tracking in MLocTracker performs quite poorly in terms of memory
+// and time on targets with a more complicated register file (FIXME).
+static cl::opt<unsigned>
+    StackSlotIdxesLimit("livedebugvalues-max-stack-slot-idxes", cl::Hidden,
+                        cl::desc("livedebugvalues-max-stack-slot-idxes"),
+                        cl::init(128));
+
 DbgOpID DbgOpID::UndefID = DbgOpID(0xffffffff);
 
 /// Tracker for converting machine value locations and variable values into
@@ -1123,6 +1132,10 @@ void MLocTracker::writeRegMask(const MachineOperand *MO, unsigned CurBB,
 }
 
 std::optional<SpillLocationNo> MLocTracker::getOrTrackSpillLoc(SpillLoc L) {
+  // Disable spill tracking on targets with a large number of slot idxes.
+  if (NumSlotIdxes >= StackSlotIdxesLimit)
+    return std::nullopt;
+
   SpillLocationNo SpillID(SpillLocs.idFor(L));
 
   if (SpillID.id() == 0) {
@@ -3707,6 +3720,15 @@ bool InstrRefBasedLDV::ExtendRanges(MachineFunction &MF,
   VTracker = nullptr;
   TTracker = nullptr;
 
+  if (MTracker->NumSlotIdxes >= StackSlotIdxesLimit) {
+    LLVM_DEBUG(
+        dbgs() << "Disabling InstrRefBasedLDV spill tracking for "
+               << MF.getName()
+               << " since target has too many potential stack slot indexes ("
+               << MTracker->NumSlotIdxes << ", limit is " << StackSlotIdxesLimit
+               << ")\n");
+  }
+
   SmallVector<MLocTransferMap, 32> MLocTransfer;
   SmallVector<VLocTracker, 8> vlocs;
   LiveInsT SavedLiveIns;

llvm/test/DebugInfo/AMDGPU/live-debug-values-spill-tracking.mir

@@ -0,0 +1,73 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx1100 -run-pass livedebugvalues %s -o - -debug-only livedebugvalues 2>&1 | FileCheck %s
+
+# REQUIRES: asserts
+
+# Verify that spill tracking is disabled on amdgcn.
+
+# CHECK: Disabling InstrRefBasedLDV spill tracking for kern since target has too many potential stack slot indexes
+
+--- |
+  define void @kern() #0 !dbg !9 {
+    ret void, !dbg !15
+  }
+
+  attributes #0 = { noinline nounwind optnone "target-cpu"="gfx1100" }
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!2, !3, !4, !5, !6, !7}
+  !llvm.ident = !{!8}
+
+  !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 19.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+  !1 = !DIFile(filename: "t.cpp", directory: "/")
+  !2 = !{i32 1, !"amdhsa_code_object_version", i32 500}
+  !3 = !{i32 7, !"Dwarf Version", i32 5}
+  !4 = !{i32 2, !"Debug Info Version", i32 3}
+  !5 = !{i32 1, !"wchar_size", i32 4}
+  !6 = !{i32 8, !"PIC Level", i32 2}
+  !7 = !{i32 7, !"frame-pointer", i32 2}
+  !8 = !{!"clang version 19.0.0"}
+  !9 = distinct !DISubprogram(name: "kern", linkageName: "kern", scope: !1, file: !1, line: 1, type: !10, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !12)
+  !10 = !DISubroutineType(types: !11)
+  !11 = !{}
+  !12 = !{!13}
+  !13 = !DILocalVariable(name: "var", scope: !9, file: !1, line: 1, type: !14)
+  !14 = !DIBasicType(name: "i32", size: 32, encoding: DW_ATE_signed)
+  !15 = !DILocation(line: 1, column: 1, scope: !9)
+
+...
+---
+name: kern
+tracksRegLiveness: true
+debugInstrRef: true
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: 0, size: 4, alignment: 4 }
+machineFunctionInfo:
+  scratchRSrcReg:  $sgpr0_sgpr1_sgpr2_sgpr3
+  stackPtrOffsetReg: '$sgpr32'
+  hasSpilledVGPRs: true
+body:             |
+  bb.0:
+    ; CHECK-LABEL: name: kern
+    ; CHECK: frame-setup CFI_INSTRUCTION escape 0x0f, 0x09, 0x90, 0x40, 0x94, 0x04, 0x36, 0x24, 0x36, 0xe9, 0x02
+    ; CHECK-NEXT: frame-setup CFI_INSTRUCTION llvm_register_pair $pc_reg, $sgpr30, 32, $sgpr31, 32
+    ; CHECK-NEXT: frame-setup CFI_INSTRUCTION undefined $vgpr0
+    ; CHECK-NEXT: DBG_INSTR_REF !13, !DIExpression(DIOpArg(0, i32)), dbg-instr-ref(1, 0), debug-location !15
+    ; CHECK-NEXT: DBG_VALUE_LIST !13, !DIExpression(DIOpArg(0, i32)), $noreg, debug-location !15
+    ; CHECK-NEXT: $vgpr0 = V_MOV_B32_e32 0, implicit $exec, debug-instr-number 1, debug-location !15
+    ; CHECK-NEXT: DBG_VALUE_LIST !13, !DIExpression(DIOpArg(0, i32)), $vgpr0, debug-location !15
+    ; CHECK-NEXT: SCRATCH_STORE_DWORD_SADDR killed $vgpr0, $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, debug-location !15 :: (store (s32) into %stack.0, addrspace 5)
+    ; CHECK-NEXT: S_NOP 0, debug-location !15
+    ; CHECK-NEXT: $vgpr0 = SCRATCH_LOAD_DWORD_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, debug-location !15 :: (load (s32) from %stack.0, addrspace 5)
+    ; CHECK-NEXT: S_ENDPGM 0, debug-location !15
+    frame-setup CFI_INSTRUCTION escape 0x0f, 0x09, 0x90, 0x40, 0x94, 0x04, 0x36, 0x24, 0x36, 0xe9, 0x02
+    frame-setup CFI_INSTRUCTION llvm_register_pair $pc_reg, $sgpr30, 32, $sgpr31, 32
+    frame-setup CFI_INSTRUCTION undefined $vgpr0
+    DBG_INSTR_REF !13, !DIExpression(DIOpArg(0, i32)), dbg-instr-ref(1, 0), debug-location !15
+    $vgpr0 = V_MOV_B32_e32 0, implicit $exec, debug-instr-number 1, debug-location !15
+    SCRATCH_STORE_DWORD_SADDR killed $vgpr0, $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, debug-location !15 :: (store (s32) into %stack.0, addrspace 5)
+    S_NOP 0, debug-location !15
+    $vgpr0 = SCRATCH_LOAD_DWORD_SADDR $sgpr32, 0, 0, implicit $exec, implicit $flat_scr, debug-location !15 :: (load (s32) from %stack.0, addrspace 5)
+    S_ENDPGM 0, debug-location !15
+
+...