Use the frame index side table for byval and inalloca arguments

[rnk]

Summary

For inalloca functions, this is a very common code pattern:

%argpack = type <{ i32, i32, i32 }>
define void @f(%argpack* inalloca %args) {
entry:
  %a = getelementptr inbounds %argpack, %argpack* %args, i32 0, i32 0
  %b = getelementptr inbounds %argpack, %argpack* %args, i32 0, i32 1
  %c = getelementptr inbounds %argpack, %argpack* %args, i32 0, i32 2
  tail call void @llvm.dbg.declare(metadata i32* %a, ... "a")
  tail call void @llvm.dbg.declare(metadata i32* %c, ... "b")
  tail call void @llvm.dbg.declare(metadata i32* %b, ... "c")

Even though these GEPs can be simplified to a constant offset from EBP
or RSP, we don't do that at -O0, and each GEP is computed into a
register. Registers used to compute argument addresses are typically
spilled and clobbered very quickly after the initial computation, so
live debug variable tracking loses information very quickly if we use
DBG_VALUE instructions.

This change moves processing of dbg.declare between argument lowering
and basic block isel, so that we can ask if an argument has a frame
index or not. If the argument lives in a register as is the case for
byval arguments on some targets, then we don't put it in the side table
and during ISel we emit DBG_VALUE instructions.

[aprantl]

This looks generally good (with outstanding comments addressed), thanks!

Is there a testcase for the example that you mention in the description?

Please keep a close eye on the green dragon bots, both the ones in the debuginfo-tests repository that execute as part of each check-clang, as well as the lldb testsuite, after landing this.

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

1183

else if ?

llvm/test/CodeGen/X86/dbg-baseptr.ll

62

please add the disassembly as a comment: (such as DW_OP_fbreg +16 )

llvm/test/DebugInfo/X86/dbg-declare-inalloca.ll

105

We typically delete all unnecessary attributes from testcases.

[rnk]

In D32980#749141, @aprantl wrote:

Is there a testcase for the example that you mention in the description?

The dbg-declare-inalloca.ll is a more real-world example of the case in the description. You need a non-trivially copyable argument to trigger inalloca.

Please keep a close eye on the green dragon bots, both the ones in the debuginfo-tests repository that execute as part of each check-clang, as well as the lldb testsuite, after landing this.

Sure!

llvm/test/CodeGen/X86/dbg-baseptr.ll

62

I understand how this is supposed to work now. I added more CHECKs to ensure that this DWARF is consistent with the asm.

llvm/test/DebugInfo/X86/dbg-declare-inalloca.ll

105

My intention is that the .ll is verbatim output from clang on the commented C++ at the beginning of the file. Is there any reason to treat reducing away attributes differently from the DI metadata, which is mostly retained below?

llvm/lib/CodeGen/SelectionDAG/FastISel.cpp

case Intrinsic::dbg_declare: {
     }
 
     const Value *Address = DI->getAddress();
     if (!Address || isa<UndefValue>(Address)) {
       DEBUG(dbgs() << "Dropping debug info for " << *DI << "\n");
       return true;
     }
 
-    unsigned Offset = 0;
+    // Byval arguments with frame indices were already handled after argument
+    // lowering and before isel.
+    const auto *Arg =
+        dyn_cast<Argument>(Address->stripInBoundsConstantOffsets());
+    if (Arg && FuncInfo.getArgumentFrameIndex(Arg) != INT_MAX)
+      return true;
+
     Optional<MachineOperand> Op;
-    if (const auto *Arg = dyn_cast<Argument>(Address))
-      // Some arguments' frame index is recorded during argument lowering.
-      Offset = FuncInfo.getArgumentFrameIndex(Arg);
-    if (Offset)
-      Op = MachineOperand::CreateFI(Offset);
-    if (!Op)
-      if (unsigned Reg = lookUpRegForValue(Address))
-        Op = MachineOperand::CreateReg(Reg, false);
 
     // If we have a VLA that has a "use" in a metadata node that's then used
     // here but it has no other uses, then we have a problem. E.g.,
     //
     //   int foo (const int *x) {
     //     char a[*x];
     //     return 0;
     //   }

llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp

 }
 
 void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
                                SelectionDAG *DAG) {
   Fn = &fn;
   MF = &mf;
   TLI = MF->getSubtarget().getTargetLowering();
   RegInfo = &MF->getRegInfo();
-  MachineModuleInfo &MMI = MF->getMMI();
   const TargetFrameLowering *TFI = MF->getSubtarget().getFrameLowering();
   unsigned StackAlign = TFI->getStackAlignment();
 
   // Check whether the function can return without sret-demotion.
   SmallVector<ISD::OutputArg, 4> Outs;
   GetReturnInfo(Fn->getReturnType(), Fn->getAttributes(), Outs, *TLI,
                 mf.getDataLayout());
   CanLowerReturn = TLI->CanLowerReturn(Fn->getCallingConv(), *MF,
for (const Instruction &I : BB) {
       }
 
       // Mark values used outside their block as exported, by allocating
       // a virtual register for them.
       if (isUsedOutsideOfDefiningBlock(&I))
         if (!isa<AllocaInst>(I) || !StaticAllocaMap.count(cast<AllocaInst>(&I)))
           InitializeRegForValue(&I);
 
-      // Collect llvm.dbg.declare information. This is done now instead of
-      // during the initial isel pass through the IR so that it is done
-      // in a predictable order.
-      if (const DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(&I)) {
-        assert(DI->getVariable() && "Missing variable");
-        assert(DI->getDebugLoc() && "Missing location");
-        if (MMI.hasDebugInfo()) {
-          // Don't handle byval struct arguments or VLAs, for example.
-          // Non-byval arguments are handled here (they refer to the stack
-          // temporary alloca at this point).
-          const Value *Address = DI->getAddress();
-          if (Address) {
-            if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Address))
-              Address = BCI->getOperand(0);
-            if (const AllocaInst *AI = dyn_cast<AllocaInst>(Address)) {
-              DenseMap<const AllocaInst *, int>::iterator SI =
-                StaticAllocaMap.find(AI);
-              if (SI != StaticAllocaMap.end()) { // Check for VLAs.
-                int FI = SI->second;
-                MF->setVariableDbgInfo(DI->getVariable(), DI->getExpression(),
-                                       FI, DI->getDebugLoc());
-              }
-            }
-          }
-        }
-      }
-
       // Decide the preferred extend type for a value.
       PreferredExtendType[&I] = getPreferredExtendForValue(&I);
     }
   }
 
   // Create an initial MachineBasicBlock for each LLVM BasicBlock in F.  This
   // also creates the initial PHI MachineInstrs, though none of the input
   // operands are populated.
void FunctionLoweringInfo::setArgumentFrameIndex(const Argument *A,
                                                  int FI) {
   ByValArgFrameIndexMap[A] = FI;
 }
 
 /// getArgumentFrameIndex - Get frame index for the byval argument.
 /// If the argument does not have any assigned frame index then 0 is
 /// returned.
 int FunctionLoweringInfo::getArgumentFrameIndex(const Argument *A) {
-  DenseMap<const Argument *, int>::iterator I =
-    ByValArgFrameIndexMap.find(A);
+  auto I = ByValArgFrameIndexMap.find(A);
   if (I != ByValArgFrameIndexMap.end())
     return I->second;
   DEBUG(dbgs() << "Argument does not have assigned frame index!\n");
-  return 0;
+  return INT_MAX;
 }
 
 unsigned FunctionLoweringInfo::getCatchPadExceptionPointerVReg(
     const Value *CPI, const TargetRegisterClass *RC) {
   MachineRegisterInfo &MRI = MF->getRegInfo();
   auto I = CatchPadExceptionPointers.insert({CPI, 0});
   unsigned &VReg = I.first->second;
   if (I.second)

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

bool SelectionDAGBuilder::EmitFuncArgumentDbgValue(
   //
   // FIXME: Should we be checking DL->inlinedAt() to determine this?
   if (!Variable->getScope()->getSubprogram()->describes(MF.getFunction()))
     return false;
 
   bool IsIndirect = false;
   Optional<MachineOperand> Op;
   // Some arguments' frame index is recorded during argument lowering.
-  if (int FI = FuncInfo.getArgumentFrameIndex(Arg))
+  int FI = FuncInfo.getArgumentFrameIndex(Arg);
+  if (FI != INT_MAX)
     Op = MachineOperand::CreateFI(FI);
 
   if (!Op && N.getNode()) {
     unsigned Reg = getUnderlyingArgReg(N);
     if (Reg && TargetRegisterInfo::isVirtualRegister(Reg)) {
       MachineRegisterInfo &RegInfo = MF.getRegInfo();
       unsigned PR = RegInfo.getLiveInPhysReg(Reg);
       if (PR)
case Intrinsic::dbg_declare: {
 
     // Check if address has undef value.
     if (isa<UndefValue>(Address) ||
         (Address->use_empty() && !isa<Argument>(Address))) {
       DEBUG(dbgs() << "Dropping debug info for " << DI << "\n");
       return nullptr;
     }
 
+    // Byval arguments with frame indices were already handled after argument
+    // lowering and before isel.
+    const auto *Arg =
+        dyn_cast<Argument>(Address->stripInBoundsConstantOffsets());
+    if (Arg && FuncInfo.getArgumentFrameIndex(Arg) != INT_MAX)
+      return nullptr;
+
     SDValue &N = NodeMap[Address];
     if (!N.getNode() && isa<Argument>(Address))
       // Check unused arguments map.
       N = UnusedArgNodeMap[Address];
     SDDbgValue *SDV;
     if (N.getNode()) {
       if (const BitCastInst *BCI = dyn_cast<BitCastInst>(Address))
         Address = BCI->getOperand(0);

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

 #include "llvm/CodeGen/GCMetadata.h"
 #include "llvm/CodeGen/MachineBasicBlock.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstr.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineMemOperand.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineOperand.h"
 #include "llvm/CodeGen/MachinePassRegistry.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/MachineValueType.h"
 #include "llvm/CodeGen/SchedulerRegistry.h"
 #include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/CodeGen/SelectionDAGISel.h"
 #include "llvm/CodeGen/SelectionDAGNodes.h"
for (const auto *SwiftErrorVal : FuncInfo->SwiftErrorVals) {
     // Keep FastIS informed about the value we just inserted.
     if (FastIS)
       FastIS->setLastLocalValue(&*std::prev(FuncInfo->InsertPt));
 
     FuncInfo->setCurrentSwiftErrorVReg(FuncInfo->MBB, SwiftErrorVal, VReg);
   }
 }
 
+/// Collect llvm.dbg.declare information. This is done after argument lowering
+/// in case the declarations refer to arguments.
+static void processDbgDeclares(FunctionLoweringInfo *FuncInfo) {
+  MachineFunction *MF = FuncInfo->MF;
+  const DataLayout &DL = MF->getDataLayout();
+  for (const BasicBlock &BB : *FuncInfo->Fn) {
+    for (const Instruction &I : BB) {
+      const DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(&I);
+      if (!DI)
+        continue;
+
+      assert(DI->getVariable() && "Missing variable");
+      assert(DI->getDebugLoc() && "Missing location");
+      const Value *Address = DI->getAddress();
+      if (!Address)
+        continue;
+
+      // Look through casts and constant offset GEPs. These mostly come from
+      // inalloca.
+      APInt Offset(DL.getPointerSizeInBits(0), 0);
+      Address = Address->stripAndAccumulateInBoundsConstantOffsets(DL, Offset);
+      int FI = INT_MAX;
+
+      // Check if the variable is a plain old static alloca. This is the common
+      // case.
+      if (const auto *AI = dyn_cast<AllocaInst>(Address)) {
+        auto SI = FuncInfo->StaticAllocaMap.find(AI);
+        if (SI != FuncInfo->StaticAllocaMap.end())
+          FI = SI->second;
+      }
+
+      // Check if the variable is a byval or inalloca argument. If it is not,
+      // then we will ignore this intrinsic and handle this during isel like
+      // dbg.value.
+      if (const auto *Arg = dyn_cast<Argument>(Address))
+        FI = FuncInfo->getArgumentFrameIndex(Arg);
+
+      if (FI == INT_MAX)
+        continue;
+
+      DIExpression *Expr = DI->getExpression();
+      if (Offset.getBoolValue())
+        Expr = DIExpression::prepend(Expr, DIExpression::NoDeref,
+                                     Offset.getZExtValue());
+      MF->setVariableDbgInfo(DI->getVariable(), Expr, FI, DI->getDebugLoc());
+    }
+  }
+}
+
 /// Propagate swifterror values through the machine function CFG.
 static void propagateSwiftErrorVRegs(FunctionLoweringInfo *FuncInfo) {
   auto *TLI = FuncInfo->TLI;
   if (!TLI->supportSwiftError())
     return;
 
   // We only need to do this when we have swifterror parameter or swifterror
   // alloc.
if (!FastIS) {
     // after them.
     if (FuncInfo->InsertPt != FuncInfo->MBB->begin())
       FastIS->setLastLocalValue(&*std::prev(FuncInfo->InsertPt));
     else
       FastIS->setLastLocalValue(nullptr);
   }
   createSwiftErrorEntriesInEntryBlock(FuncInfo, FastIS, TLI, TII, SDB);
 
+  processDbgDeclares(FuncInfo);
+
   // Iterate over all basic blocks in the function.
   for (const BasicBlock *LLVMBB : RPOT) {
     if (OptLevel != CodeGenOpt::None) {
       bool AllPredsVisited = true;
       for (const_pred_iterator PI = pred_begin(LLVMBB), PE = pred_end(LLVMBB);
            PI != PE; ++PI) {
         if (!FuncInfo->VisitedBBs.count(*PI)) {
           AllPredsVisited = false;

llvm/test/CodeGen/X86/2010-01-18-DbgValue.ll

-; RUN: llc -march=x86 -O0 < %s | FileCheck %s
-; Currently, dbg.declare generates a DEBUG_VALUE comment.  Eventually it will
-; generate DWARF and this test will need to be modified or removed.
+; RUN: llc -march=x86 -O0 < %s -filetype=obj | llvm-dwarfdump - | FileCheck %s
 
+; CHECK-LABEL: .debug_info contents:
+
+; CHECK-LABEL: DW_TAG_subprogram
+; CHECK:   DW_AT_name [DW_FORM_strp]       ( {{.*}}"foo")
+; CHECK:   DW_TAG_formal_parameter
+; CHECK-NEXT:     DW_AT_location [DW_FORM_exprloc]      (<0x2> 91 08 )
+; CHECK-NEXT:     DW_AT_name [DW_FORM_strp]     ( {{.*}}"my_r0")
 
 %struct.Pt = type { double, double }
 %struct.Rect = type { %struct.Pt, %struct.Pt }
 
 define double @foo(%struct.Rect* byval %my_r0) nounwind ssp !dbg !1 {
 entry:
-;CHECK: DEBUG_VALUE
   %retval = alloca double                         ; <double*> [#uses=2]
   %0 = alloca double                              ; <double*> [#uses=2]
   %"alloca point" = bitcast i32 0 to i32          ; <i32> [#uses=0]
   call void @llvm.dbg.declare(metadata %struct.Rect* %my_r0, metadata !0, metadata !DIExpression()), !dbg !15
   %1 = getelementptr inbounds %struct.Rect, %struct.Rect* %my_r0, i32 0, i32 0, !dbg !16 ; <%struct.Pt*> [#uses=1]
   %2 = getelementptr inbounds %struct.Pt, %struct.Pt* %1, i32 0, i32 0, !dbg !16 ; <double*> [#uses=1]
   %3 = load double, double* %2, align 8, !dbg !16         ; <double> [#uses=1]
   store double %3, double* %0, align 8, !dbg !16

llvm/test/CodeGen/X86/2012-11-30-handlemove-dbg.ll

-; RUN: llc < %s -mtriple=x86_64-apple-macosx -enable-misched \
-; RUN:          -verify-machineinstrs | FileCheck %s
-;
-; Test LiveInterval update handling of DBG_VALUE.
-; rdar://12777252.
-;
-; CHECK: %entry
-; CHECK: DEBUG_VALUE: subdivp:hg
-; CHECK: j
-
-%struct.node.0.27 = type { i16, double, [3 x double], i32, i32 }
-%struct.hgstruct.2.29 = type { %struct.bnode.1.28*, [3 x double], double, [3 x double] }
-%struct.bnode.1.28 = type { i16, double, [3 x double], i32, i32, [3 x double], [3 x double], [3 x double], double, %struct.bnode.1.28*, %struct.bnode.1.28* }
-
-declare void @llvm.dbg.declare(metadata, metadata, metadata) nounwind readnone
-
-define signext i16 @subdivp(%struct.node.0.27* nocapture %p, double %dsq, double %tolsq, %struct.hgstruct.2.29* nocapture byval align 8 %hg) nounwind uwtable readonly ssp !dbg !14 {
-entry:
-  call void @llvm.dbg.declare(metadata %struct.hgstruct.2.29* %hg, metadata !4, metadata !DIExpression()), !dbg !DILocation(scope: !14)
-  %type = getelementptr inbounds %struct.node.0.27, %struct.node.0.27* %p, i64 0, i32 0
-  %0 = load i16, i16* %type, align 2
-  %cmp = icmp eq i16 %0, 1
-  br i1 %cmp, label %return, label %for.cond.preheader
-
-for.cond.preheader:                               ; preds = %entry
-  %arrayidx6.1 = getelementptr inbounds %struct.hgstruct.2.29, %struct.hgstruct.2.29* %hg, i64 0, i32 1, i64 1
-  %cmp22 = fcmp olt double 0.000000e+00, %dsq
-  %conv24 = zext i1 %cmp22 to i16
-  br label %return
-
-return:                                           ; preds = %for.cond.preheader, %entry
-  %retval.0 = phi i16 [ %conv24, %for.cond.preheader ], [ 0, %entry ]
-  ret i16 %retval.0
-}
-
-declare void @llvm.dbg.value(metadata, i64, metadata, metadata) nounwind readnone
-
-!llvm.dbg.cu = !{!0}
-!llvm.module.flags = !{!12}
-
-!0 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang version 3.3 (trunk 168918) (llvm/trunk 168920)", isOptimized: true, emissionKind: FullDebug, file: !11, enums: !2, retainedTypes: !2, globals: !2)
-!2 = !{}
-!4 = !DILocalVariable(name: "hg", line: 725, arg: 4, scope: !14, file: !5, type: !6)
-!5 = !DIFile(filename: "MultiSource/Benchmarks/Olden/bh/newbh.c", directory: "MultiSource/Benchmarks/Olden/bh")
-!6 = !DIDerivedType(tag: DW_TAG_typedef, name: "hgstruct", line: 492, file: !11, baseType: !7)
-!7 = !DICompositeType(tag: DW_TAG_structure_type, line: 487, size: 512, align: 64, file: !11)
-!11 = !DIFile(filename: "MultiSource/Benchmarks/Olden/bh/newbh.c", directory: "MultiSource/Benchmarks/Olden/bh")
-!12 = !{i32 1, !"Debug Info Version", i32 3}
-!14 = distinct !DISubprogram(name: "subdivp", isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, unit: !0, scopeLine: 1, file: !11, scope: !5, type: !15)
-!15 = !DISubroutineType(types: !16)
-!16 = !{null}

llvm/test/CodeGen/X86/dbg-baseptr.ll

 ; RUN: llc -o - %s | FileCheck %s
+; RUN: llc -filetype=obj -o - %s | llvm-dwarfdump - | FileCheck %s --check-prefix=DWARF
 ; This test checks that parameters on the stack pointer are correctly
 ; referenced by debug info.
 target triple = "x86_64--"
 
 @glob = external global i64
 @ptr = external global i32*
 %struct.s = type { i32, i32, i32, i32, i32 }
 
 ; CHECK-LABEL: f0:
-; CHECK: DEBUG_VALUE: f:input <- [%RSP+8]
 define i32 @f0(%struct.s* byval align 8 %input) !dbg !8 {
   call void @llvm.dbg.declare(metadata %struct.s* %input, metadata !4, metadata !17), !dbg !18
-  ret i32 42
+  ret i32 42, !dbg !18
 }
 
+; DWARF-LABEL: .debug_info contents:
+
+; DWARF-LABEL: DW_TAG_subprogram
+; DWARF:   DW_AT_name [DW_FORM_strp]       ( {{.*}}"f0")
+; DWARF:   DW_TAG_formal_parameter
+; DWARF-NEXT:     DW_AT_location [DW_FORM_exprloc]      (<0x2> 91 08 )
+; DWARF-NEXT:     DW_AT_name [DW_FORM_strp]     ( {{.*}}"input")
+
 ; CHECK-LABEL: f1:
-; CHECK: DEBUG_VALUE: f:input <- [%RBP+16]
 define i32 @f1(%struct.s* byval align 8 %input) !dbg !19 {
   %val = load i64, i64* @glob
   ; this alloca should force FP usage.
   %stackspace = alloca i32, i64 %val, align 1
   store i32* %stackspace, i32** @ptr
   call void @llvm.dbg.declare(metadata %struct.s* %input, metadata !20, metadata !17), !dbg !21
-  ret i32 42
+  ret i32 42, !dbg !21
 }
 
+; DWARF-LABEL: DW_TAG_subprogram
+; DWARF:   DW_AT_name [DW_FORM_strp]       ( {{.*}}"f1")
+; DWARF:   DW_TAG_formal_parameter
+; DWARF-NEXT:     DW_AT_location [DW_FORM_exprloc]      (<0x2> 91 10 )
+; DWARF-NEXT:     DW_AT_name [DW_FORM_strp]     ( {{.*}}"input")
+
 ; CHECK-LABEL: f2:
 ; Just check that we are indeed aligning the stack and setting up a base pointer
 ; in RBX.
 ; CHECK: pushq %rbp
 ; CHECK: movq %rsp, %rbp
 ; CHECK: pushq %rbx
 ; CHECK: andq $-64, %rsp
 ; CHECK: subq $64, %rsp
 ; CHECK: movq %rsp, %rbx
-; The parameter should still be referenced through RBP though.
-; CHECK-NOT: DEBUG_VALUE: f:input <- [%RBX
-; CHECK: DEBUG_VALUE: f:input <- [%RBP+16]
 define i32 @f2(%struct.s* byval align 8 %input) !dbg !22 {
   %val = load i64, i64* @glob
   %stackspace = alloca i32, i64 %val, align 64
   store i32* %stackspace, i32** @ptr
   call void @llvm.dbg.declare(metadata %struct.s* %input, metadata !23, metadata !17), !dbg !24
-  ret i32 42
+  ret i32 42, !dbg !24
 }
 
+; "input" should still be referred to through RBP.
+; DWARF-LABEL: DW_TAG_subprogram
+; DWARF:   DW_AT_name [DW_FORM_strp]       ( {{.*}}"f2")
+; DWARF:   DW_TAG_formal_parameter
+; DWARF-NEXT:     DW_AT_location [DW_FORM_exprloc]      (<0x2> 91 10 )
+; DWARF-NEXT:     DW_AT_name [DW_FORM_strp]     ( {{.*}}"input")
+
 declare void @llvm.dbg.declare(metadata, metadata, metadata)
 
 !llvm.dbg.cu = !{!2}
 !llvm.module.flags = !{!0, !1}
 
 !0 = !{i32 2, !"Dwarf Version", i32 4}
 !1 = !{i32 2, !"Debug Info Version", i32 3}
-!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, emissionKind: FullDebug)
 !3 = !DIFile(filename: "dbg-baseptr.ll", directory: "/")
 !4 = !DILocalVariable(name: "input", arg: 1, scope: !8, file: !3, line: 5, type: !9)
 !5 = !{}
 
 !6 = !DISubroutineType(types: !7)
 !7 = !{!10, !9}
 
-!8 = distinct !DISubprogram(name: "f", file: !3, line: 5, type: !6, isLocal: false, isDefinition: true, flags: DIFlagPrototyped, unit: !2, variables: !5)
+!8 = distinct !DISubprogram(name: "f0", file: !3, line: 5, type: !6, isLocal: false, isDefinition: true, unit: !2, variables: !5)
 
 !9 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "s", elements: !11)
 !10 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
 !11 = !{!12, !13, !14, !15, !16}
 !12 = !DIDerivedType(tag: DW_TAG_member, name: "a", baseType: !10, size: 32)
 !13 = !DIDerivedType(tag: DW_TAG_member, name: "b", baseType: !10, size: 32, offset: 32)
 !14 = !DIDerivedType(tag: DW_TAG_member, name: "c", baseType: !10, size: 32, offset: 64)
 !15 = !DIDerivedType(tag: DW_TAG_member, name: "d", baseType: !10, size: 32, offset: 96)
 !16 = !DIDerivedType(tag: DW_TAG_member, name: "e", baseType: !10, size: 32, offset: 128)
 
 !17 = !DIExpression()
 !18 = !DILocation(line: 5, scope: !8)
 
-!19 = distinct !DISubprogram(name: "f", file: !3, line: 5, type: !6, isLocal: false, isDefinition: true, flags: DIFlagPrototyped, unit: !2, variables: !5)
+!19 = distinct !DISubprogram(name: "f1", file: !3, line: 5, type: !6, isLocal: false, isDefinition: true, flags: DIFlagPrototyped, unit: !2, variables: !5)
 !20 = !DILocalVariable(name: "input", arg: 1, scope: !19, file: !3, line: 5, type: !9)
 !21 = !DILocation(line: 5, scope: !19)
-!22 = distinct !DISubprogram(name: "f", file: !3, line: 5, type: !6, isLocal: false, isDefinition: true, flags: DIFlagPrototyped, unit: !2, variables: !5)
+!22 = distinct !DISubprogram(name: "f2", file: !3, line: 5, type: !6, isLocal: false, isDefinition: true, flags: DIFlagPrototyped, unit: !2, variables: !5)
 !23 = !DILocalVariable(name: "input", arg: 1, scope: !22, file: !3, line: 5, type: !9)
 !24 = !DILocation(line: 5, scope: !22)

llvm/test/DebugInfo/X86/dbg-declare-inalloca.ll

+; RUN: llc -O0 < %s | FileCheck %s --check-prefix=CHECK --check-prefix=DEBUG
+; RUN: llc < %s | FileCheck %s
+
+; IR generated by the following source:
+; struct NonTrivial {
+;   NonTrivial();// : x(42) {}
+;   ~NonTrivial();// {}
+;   int x;
+; };
+; extern "C" void g(int);// {}
+; extern "C" void h(int);// {}
+; extern "C" void f(NonTrivial a, int b, int unused, int c) {
+;   if (b) {
+;     g(c);
+;   } else {
+;     h(a.x);
+;   }
+;   (void)unused;
+; }
+; //int main() {
+; //  NonTrivial x;
+; //  f(x, 1, 2, 3);
+; //}
+;
+; Remove C++ comments to have a complete, debuggable program.
+
+; We don't need (or want) DBG_VALUE instructions to describe the location of
+; inalloca arguments. We want frame indices in the side table, especially at
+; -O0, because they are reliable across the entire function and don't require
+; any propagation or analysis.
+
+; CHECK: _f:                                     # @f
+; CHECK: Lfunc_begin0:
+; CHECK-NOT: DEBUG_VALUE
+; CHECK: [[start:Ltmp[0-9]+]]:
+; CHECK-NOT: DEBUG_VALUE
+; CHECK:         cmpl
+; CHECK:         calll   _g
+; CHECK:         calll   _h
+; CHECK:         jmp "??1NonTrivial@@QAE@XZ"
+; CHECK: [[end:Ltmp[0-9]+]]:
+; CHECK: Lfunc_end0:
+
+; FIXME: Optimized debug info should preserve this.
+; DEBUG:         .short  4414                    # Record kind: S_LOCAL
+; DEBUG:         .asciz  "a"
+; DEBUG:         .cv_def_range    [[start]] [[end]]
+
+; CHECK:         .short  4414                    # Record kind: S_LOCAL
+; CHECK:         .asciz  "b"
+; CHECK:         .cv_def_range    [[start]] [[end]]
+
+; CHECK:         .short  4414                    # Record kind: S_LOCAL
+; CHECK:         .asciz  "c"
+; CHECK:         .cv_def_range    [[start]] [[end]]
+
+
+
+; ModuleID = 't.cpp'
+source_filename = "t.cpp"
+target datalayout = "e-m:x-p:32:32-i64:64-f80:32-n8:16:32-a:0:32-S32"
+target triple = "i386-pc-windows-msvc19.10.24728"
+
+%struct.NonTrivial = type { i32 }
+
+; Function Attrs: nounwind
+define void @f(<{ %struct.NonTrivial, i32, i32, i32 }>* inalloca) local_unnamed_addr #0 !dbg !7 {
+entry:
+  %a = getelementptr inbounds <{ %struct.NonTrivial, i32, i32, i32 }>, <{ %struct.NonTrivial, i32, i32, i32 }>* %0, i32 0, i32 0
+  %b = getelementptr inbounds <{ %struct.NonTrivial, i32, i32, i32 }>, <{ %struct.NonTrivial, i32, i32, i32 }>* %0, i32 0, i32 1
+  tail call void @llvm.dbg.declare(metadata i32* %c, metadata !20, metadata !24), !dbg !25
+  tail call void @llvm.dbg.declare(metadata i32* %b, metadata !22, metadata !24), !dbg !26
+  tail call void @llvm.dbg.declare(metadata %struct.NonTrivial* %a, metadata !23, metadata !24), !dbg !27
+  %1 = load i32, i32* %b, align 4, !dbg !28, !tbaa !30
+  %tobool = icmp eq i32 %1, 0, !dbg !28
+  br i1 %tobool, label %if.else, label %if.then, !dbg !34
+
+if.then:                                          ; preds = %entry
+  %c = getelementptr inbounds <{ %struct.NonTrivial, i32, i32, i32 }>, <{ %struct.NonTrivial, i32, i32, i32 }>* %0, i32 0, i32 3
+  %2 = load i32, i32* %c, align 4, !dbg !35, !tbaa !30
+  tail call void @g(i32 %2) #4, !dbg !37
+  br label %if.end, !dbg !38
+
+if.else:                                          ; preds = %entry
+  %x = getelementptr inbounds <{ %struct.NonTrivial, i32, i32, i32 }>, <{ %struct.NonTrivial, i32, i32, i32 }>* %0, i32 0, i32 0, i32 0, !dbg !39
+  %3 = load i32, i32* %x, align 4, !dbg !39, !tbaa !41
+  tail call void @h(i32 %3) #4, !dbg !43
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  tail call x86_thiscallcc void @"\01??1NonTrivial@@QAE@XZ"(%struct.NonTrivial* nonnull %a) #4, !dbg !44
+  ret void, !dbg !44
+}
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+declare void @g(i32) local_unnamed_addr #2
+
+declare void @h(i32) local_unnamed_addr #2
+
+; Function Attrs: nounwind
+declare x86_thiscallcc void @"\01??1NonTrivial@@QAE@XZ"(%struct.NonTrivial*) unnamed_addr #3
+
+attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="pentium4" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone speculatable }
+attributes #2 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="pentium4" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #3 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="pentium4" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #4 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 5.0.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "t.cpp", directory: "C:\5Csrc\5Cllvm-project\5Cbuild", checksumkind: CSK_MD5, checksum: "e41e3fda2a91b52e121ed6c29a209eae")
+!2 = !{}
+!3 = !{i32 1, !"NumRegisterParameters", i32 0}
+!4 = !{i32 2, !"CodeView", i32 1}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = !{!"clang version 5.0.0 "}
+!7 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 8, type: !8, isLocal: false, isDefinition: true, scopeLine: 8, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !19)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10, !13, !13, !13}
+!10 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "NonTrivial", file: !1, line: 1, size: 32, elements: !11, identifier: ".?AUNonTrivial@@")
+!11 = !{!12, !14, !18}
+!12 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !10, file: !1, line: 4, baseType: !13, size: 32)
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !DISubprogram(name: "NonTrivial", scope: !10, file: !1, line: 2, type: !15, isLocal: false, isDefinition: false, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: true)
+!15 = !DISubroutineType(cc: DW_CC_BORLAND_thiscall, types: !16)
+!16 = !{null, !17}
+!17 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !10, size: 32, flags: DIFlagArtificial | DIFlagObjectPointer)
+!18 = !DISubprogram(name: "~NonTrivial", scope: !10, file: !1, line: 3, type: !15, isLocal: false, isDefinition: false, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true)
+!19 = !{!20, !21, !22, !23}
+!20 = !DILocalVariable(name: "c", arg: 4, scope: !7, file: !1, line: 8, type: !13)
+!21 = !DILocalVariable(name: "unused", arg: 3, scope: !7, file: !1, line: 8, type: !13)
+!22 = !DILocalVariable(name: "b", arg: 2, scope: !7, file: !1, line: 8, type: !13)
+!23 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 8, type: !10)
+!24 = !DIExpression()
+!25 = !DILocation(line: 8, column: 56, scope: !7)
+!26 = !DILocation(line: 8, column: 37, scope: !7)
+!27 = !DILocation(line: 8, column: 30, scope: !7)
+!28 = !DILocation(line: 9, column: 7, scope: !29)
+!29 = distinct !DILexicalBlock(scope: !7, file: !1, line: 9, column: 7)
+!30 = !{!31, !31, i64 0}
+!31 = !{!"int", !32, i64 0}
+!32 = !{!"omnipotent char", !33, i64 0}
+!33 = !{!"Simple C++ TBAA"}
+!34 = !DILocation(line: 9, column: 7, scope: !7)
+!35 = !DILocation(line: 10, column: 7, scope: !36)
+!36 = distinct !DILexicalBlock(scope: !29, file: !1, line: 9, column: 10)
+!37 = !DILocation(line: 10, column: 5, scope: !36)
+!38 = !DILocation(line: 11, column: 3, scope: !36)
+!39 = !DILocation(line: 12, column: 9, scope: !40)
+!40 = distinct !DILexicalBlock(scope: !29, file: !1, line: 11, column: 10)
+!41 = !{!42, !31, i64 0}
+!42 = !{!"?AUNonTrivial@@", !31, i64 0}
+!43 = !DILocation(line: 12, column: 5, scope: !40)
+!44 = !DILocation(line: 15, column: 1, scope: !7)