Reapply an improved version of r180816/180817.

Change the informal convention of DBG_VALUE machine instructions so that
we can express a register-indirect address with an offset of 0.
The old convention was that a DBG_VALUE is a register-indirect value if
the offset (operand 1) is nonzero. The new convention is that a DBG_VALUE
is register-indirect if the first operand is a register and the second
operand is an immediate. For plain register values the combination reg,
reg is used. MachineInstrBuilder::BuildMI knows how to build the new
DBG_VALUES.

rdar://problem/13658587

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185966 91177308-0d34-0410-b5e6-96231b3b80d8

14 files changed, 237 insertions, 54 deletions

diff --git a/include/llvm/CodeGen/MachineInstrBuilder.h b/include/llvm/CodeGen/MachineInstrBuilder.h
index 92c8da991c..df01371a47 100644
--- a/include/llvm/CodeGen/MachineInstrBuilder.h
+++ b/include/llvm/CodeGen/MachineInstrBuilder.h
@@ -335,6 +335,51 @@ inline MachineInstrBuilder BuildMI(MachineBasicBlock *BB,
   return BuildMI(*BB, BB->end(), DL, MCID, DestReg);
 }
 
+/// BuildMI - This version of the builder builds a DBG_VALUE intrinsic
+/// for either a value in a register or a register-indirect+offset
+/// address.  The convention is that a DBG_VALUE is indirect iff the
+/// second operand is an immediate.
+///
+inline MachineInstrBuilder BuildMI(MachineFunction &MF,
+                                   DebugLoc DL,
+                                   const MCInstrDesc &MCID,
+                                   bool IsIndirect,
+                                   unsigned Reg,
+                                   unsigned Offset,
+                                   const MDNode *MD) {
+  if (IsIndirect)
+    return BuildMI(MF, DL, MCID)
+      .addReg(Reg, RegState::Debug)
+      .addImm(Offset)
+      .addMetadata(MD);
+  else {
+    assert(Offset == 0 && "A direct address cannot have an offset.");
+    return BuildMI(MF, DL, MCID)
+      .addReg(Reg, RegState::Debug)
+      .addReg(0U, RegState::Debug)
+      .addMetadata(MD);
+  }
+}
+
+/// BuildMI - This version of the builder builds a DBG_VALUE intrinsic
+/// for either a value in a register or a register-indirect+offset
+/// address and inserts it at position I.
+///
+inline MachineInstrBuilder BuildMI(MachineBasicBlock &BB,
+                                   MachineBasicBlock::iterator I,
+                                   DebugLoc DL,
+                                   const MCInstrDesc &MCID,
+                                   bool IsIndirect,
+                                   unsigned Reg,
+                                   unsigned Offset,
+                                   const MDNode *MD) {
+  MachineFunction &MF = *BB.getParent();
+  MachineInstr *MI = BuildMI(MF, DL, MCID, IsIndirect, Reg, Offset, MD);
+  BB.insert(I, MI);
+  return MachineInstrBuilder(MF, MI);
+}
+
+
 inline unsigned getDefRegState(bool B) {
   return B ? RegState::Define : 0;
 }
diff --git a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 52e52b4162..7c10bd6a1b 100644
--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -570,8 +570,10 @@ static bool emitDebugValueComment(const MachineInstr *MI, AsmPrinter &AP) {
   }
   OS << V.getName() << " <- ";
 
-  int64_t Offset = MI->getOperand(1).getImm();
-  bool Deref = false;
+  // The second operand is only an offset if it's an immediate.
+  bool Deref = MI->getOperand(0).isReg() && MI->getOperand(1).isImm();
+  int64_t Offset = Deref ? MI->getOperand(1).getImm() : 0;
+
   // Register or immediate value. Register 0 means undef.
   if (MI->getOperand(0).isFPImm()) {
     APFloat APF = APFloat(MI->getOperand(0).getFPImm()->getValueAPF());
@@ -595,8 +597,6 @@ static bool emitDebugValueComment(const MachineInstr *MI, AsmPrinter &AP) {
     unsigned Reg;
     if (MI->getOperand(0).isReg()) {
       Reg = MI->getOperand(0).getReg();
-      Deref = Offset != 0; // FIXME: use a better sentinel value so that deref
-                           // of a reg with a zero offset is valid
     } else {
       assert(MI->getOperand(0).isFI() && "Unknown operand type");
       const TargetFrameLowering *TFI = AP.TM.getFrameLowering();
@@ -616,10 +616,9 @@ static bool emitDebugValueComment(const MachineInstr *MI, AsmPrinter &AP) {
     OS << AP.TM.getRegisterInfo()->getName(Reg);
   }
 
-  if (Offset)
-    OS << '+' << Offset;
   if (Deref)
-    OS << ']';
+    OS << '+' << Offset << ']';
+
   // NOTE: Want this comment at start of line, don't emit with AddComment.
   AP.OutStreamer.EmitRawText(OS.str());
   return true;
diff --git a/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index ec7c5bfa4e..3e6db1cc50 100644
--- a/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -1563,8 +1563,9 @@ DIE *CompileUnit::constructVariableDIE(DbgVariable *DV,
     assert(DVInsn->getNumOperands() == 3);
     if (DVInsn->getOperand(0).isReg()) {
       const MachineOperand RegOp = DVInsn->getOperand(0);
-      if (int64_t Offset = DVInsn->getOperand(1).getImm()) {
-        MachineLocation Location(RegOp.getReg(), Offset);
+      // If the second operand is an immedieate, this is an indirect value.
+      if (DVInsn->getOperand(1).isImm()) {
+        MachineLocation Location(RegOp.getReg(), DVInsn->getOperand(1).getImm());
         addVariableAddress(*DV, VariableDie, Location);
       } else if (RegOp.getReg())
         addVariableAddress(*DV, VariableDie, MachineLocation(RegOp.getReg()));
diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index dbac80a9d3..4142480902 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -1184,7 +1184,8 @@ static bool isDbgValueInDefinedReg(const MachineInstr *MI) {
   assert(MI->isDebugValue() && "Invalid DBG_VALUE machine instruction!");
   return MI->getNumOperands() == 3 &&
          MI->getOperand(0).isReg() && MI->getOperand(0).getReg() &&
-         MI->getOperand(1).isImm() && MI->getOperand(1).getImm() == 0;
+         (MI->getOperand(1).isImm() ||
+          (MI->getOperand(1).isReg() && MI->getOperand(1).getReg() == 0U));
 }
 
 // Get .debug_loc entry for the instruction range starting at MI.
@@ -1195,12 +1196,11 @@ static DotDebugLocEntry getDebugLocEntry(AsmPrinter *Asm,
   const MDNode *Var =  MI->getOperand(MI->getNumOperands() - 1).getMetadata();
 
   assert(MI->getNumOperands() == 3);
-  if (MI->getOperand(0).isReg() && MI->getOperand(1).isImm()) {
+  if (MI->getOperand(0).isReg()) {
     MachineLocation MLoc;
-    // TODO: Currently an offset of 0 in a DBG_VALUE means
-    // we need to generate a direct register value.
-    // There is no way to specify an indirect value with offset 0.
-    if (MI->getOperand(1).getImm() == 0)
+    // If the second operand is an immediate, this is a
+    // register-indirect address.
+    if (!MI->getOperand(1).isImm())
       MLoc.set(MI->getOperand(0).getReg());
     else
       MLoc.set(MI->getOperand(0).getReg(), MI->getOperand(1).getImm());
diff --git a/lib/CodeGen/LiveDebugVariables.cpp b/lib/CodeGen/LiveDebugVariables.cpp
index 5837f0cccb..85bed46569 100644
--- a/lib/CodeGen/LiveDebugVariables.cpp
+++ b/lib/CodeGen/LiveDebugVariables.cpp
@@ -108,6 +108,7 @@ class LDVImpl;
 class UserValue {
   const MDNode *variable; ///< The debug info variable we are part of.
   unsigned offset;        ///< Byte offset into variable.
+  bool IsIndirect;        ///< true if this is a register-indirect+offset value.
   DebugLoc dl;            ///< The debug location for the variable. This is
                           ///< used by dwarf writer to find lexical scope.
   UserValue *leader;      ///< Equivalence class leader.
@@ -134,9 +135,10 @@ class UserValue {
 
 public:
   /// UserValue - Create a new UserValue.
-  UserValue(const MDNode *var, unsigned o, DebugLoc L,
+  UserValue(const MDNode *var, unsigned o, bool i, DebugLoc L,
             LocMap::Allocator &alloc)
-    : variable(var), offset(o), dl(L), leader(this), next(0), locInts(alloc)
+    : variable(var), offset(o), IsIndirect(i), dl(L), leader(this),
+      next(0), locInts(alloc)
   {}
 
   /// getLeader - Get the leader of this value's equivalence class.
@@ -299,7 +301,8 @@ class LDVImpl {
   UVMap userVarMap;
 
   /// getUserValue - Find or create a UserValue.
-  UserValue *getUserValue(const MDNode *Var, unsigned Offset, DebugLoc DL);
+  UserValue *getUserValue(const MDNode *Var, unsigned Offset,
+                          bool IsIndirect, DebugLoc DL);
 
   /// lookupVirtReg - Find the EC leader for VirtReg or null.
   UserValue *lookupVirtReg(unsigned VirtReg);
@@ -414,7 +417,7 @@ void UserValue::mapVirtRegs(LDVImpl *LDV) {
 }
 
 UserValue *LDVImpl::getUserValue(const MDNode *Var, unsigned Offset,
-                                 DebugLoc DL) {
+                                 bool IsIndirect, DebugLoc DL) {
   UserValue *&Leader = userVarMap[Var];
   if (Leader) {
     UserValue *UV = Leader->getLeader();
@@ -424,7 +427,7 @@ UserValue *LDVImpl::getUserValue(const MDNode *Var, unsigned Offset,
         return UV;
   }
 
-  UserValue *UV = new UserValue(Var, Offset, DL, allocator);
+  UserValue *UV = new UserValue(Var, Offset, IsIndirect, DL, allocator);
   userValues.push_back(UV);
   Leader = UserValue::merge(Leader, UV);
   return UV;
@@ -445,15 +448,17 @@ UserValue *LDVImpl::lookupVirtReg(unsigned VirtReg) {
 bool LDVImpl::handleDebugValue(MachineInstr *MI, SlotIndex Idx) {
   // DBG_VALUE loc, offset, variable
   if (MI->getNumOperands() != 3 ||
-      !MI->getOperand(1).isImm() || !MI->getOperand(2).isMetadata()) {
+      !(MI->getOperand(1).isReg() || MI->getOperand(1).isImm()) ||
+      !MI->getOperand(2).isMetadata()) {
     DEBUG(dbgs() << "Can't handle " << *MI);
     return false;
   }
 
   // Get or create the UserValue for (variable,offset).
-  unsigned Offset = MI->getOperand(1).getImm();
+  bool IsIndirect = MI->getOperand(1).isImm();
+  unsigned Offset = IsIndirect ? MI->getOperand(1).getImm() : 0;
   const MDNode *Var = MI->getOperand(2).getMetadata();
-  UserValue *UV = getUserValue(Var, Offset, MI->getDebugLoc());
+  UserValue *UV = getUserValue(Var, Offset, IsIndirect, MI->getDebugLoc());
   UV->addDef(Idx, MI->getOperand(0));
   return true;
 }
@@ -921,8 +926,12 @@ void UserValue::insertDebugValue(MachineBasicBlock *MBB, SlotIndex Idx,
   MachineOperand &Loc = locations[LocNo];
   ++NumInsertedDebugValues;
 
-  BuildMI(*MBB, I, findDebugLoc(), TII.get(TargetOpcode::DBG_VALUE))
-    .addOperand(Loc).addImm(offset).addMetadata(variable);
+  if (Loc.isReg())
+    BuildMI(*MBB, I, findDebugLoc(), TII.get(TargetOpcode::DBG_VALUE),
+            IsIndirect, Loc.getReg(), offset, variable);
+  else
+    BuildMI(*MBB, I, findDebugLoc(), TII.get(TargetOpcode::DBG_VALUE))
+      .addOperand(Loc).addImm(offset).addMetadata(variable);
 }
 
 void UserValue::emitDebugValues(VirtRegMap *VRM, LiveIntervals &LIS,
diff --git a/lib/CodeGen/RegAllocFast.cpp b/lib/CodeGen/RegAllocFast.cpp
index 2e9c02077b..cd8b66469f 100644
--- a/lib/CodeGen/RegAllocFast.cpp
+++ b/lib/CodeGen/RegAllocFast.cpp
@@ -298,7 +298,8 @@ void RAFast::spillVirtReg(MachineBasicBlock::iterator MI,
     for (unsigned li = 0, le = LRIDbgValues.size(); li != le; ++li) {
       MachineInstr *DBG = LRIDbgValues[li];
       const MDNode *MDPtr = DBG->getOperand(2).getMetadata();
-      int64_t Offset = DBG->getOperand(1).getImm();
+      bool IsIndirect = DBG->getOperand(1).isImm(); // Register-indirect value?
+      int64_t Offset = IsIndirect ? DBG->getOperand(1).getImm() : 0;
       DebugLoc DL;
       if (MI == MBB->end()) {
         // If MI is at basic block end then use last instruction's location.
diff --git a/lib/CodeGen/SelectionDAG/FastISel.cpp b/lib/CodeGen/SelectionDAG/FastISel.cpp
index cb55324aec..14a2b005c0 100644
--- a/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -612,11 +612,13 @@ bool FastISel::SelectCall(const User *I) {
       return true;
     }
 
+    unsigned Offset = 0;
     Optional<MachineOperand> Op;
     if (const Argument *Arg = dyn_cast<Argument>(Address))
       // Some arguments' frame index is recorded during argument lowering.
-      if (int FI = FuncInfo.getArgumentFrameIndex(Arg))
-        Op = MachineOperand::CreateFI(FI);
+      Offset = FuncInfo.getArgumentFrameIndex(Arg);
+    if (Offset)
+        Op = MachineOperand::CreateFI(Offset);
     if (!Op)
       if (unsigned Reg = lookUpRegForValue(Address))
         Op = MachineOperand::CreateReg(Reg, false);
@@ -638,12 +640,16 @@ bool FastISel::SelectCall(const User *I) {
       Op = MachineOperand::CreateReg(FuncInfo.InitializeRegForValue(Address),
                                       false);
 
-    if (Op && Op->isReg())
-      Op->setIsDebug(true);
-
     if (Op)
-      BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
-              TII.get(TargetOpcode::DBG_VALUE)).addOperand(*Op).addImm(0)
+      if (Op->isReg()) {
+        Op->setIsDebug(true);
+        BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
+                TII.get(TargetOpcode::DBG_VALUE),
+                /* IsIndirect */ DI->getAddress()->getType()->isPointerTy(),
+                Op->getReg(), Offset, DI->getVariable());
+      } else
+        BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL,
+                TII.get(TargetOpcode::DBG_VALUE)).addOperand(*Op).addImm(0)
           .addMetadata(DI->getVariable());
     else
       // We can't yet handle anything else here because it would require
@@ -676,9 +682,9 @@ bool FastISel::SelectCall(const User *I) {
         .addFPImm(CF).addImm(DI->getOffset())
         .addMetadata(DI->getVariable());
     } else if (unsigned Reg = lookUpRegForValue(V)) {
-      BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II)
-        .addReg(Reg, RegState::Debug).addImm(DI->getOffset())
-        .addMetadata(DI->getVariable());
+      bool IsIndirect = DI->getOffset() != 0;
+      BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DL, II, IsIndirect,
+              Reg, DI->getOffset(), DI->getVariable());
     } else {
       // We can't yet handle anything else here because it would require
       // generating code, thus altering codegen because of debug info.
diff --git a/lib/CodeGen/SelectionDAG/InstrEmitter.cpp b/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
index 0639238b1e..e107276359 100644
--- a/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
+++ b/lib/CodeGen/SelectionDAG/InstrEmitter.cpp
@@ -678,7 +678,13 @@ InstrEmitter::EmitDbgValue(SDDbgValue *SD,
     MIB.addReg(0U);
   }
 
-  MIB.addImm(Offset).addMetadata(MDPtr);
+  if (Offset != 0) // Indirect addressing.
+    MIB.addImm(Offset);
+  else
+    MIB.addReg(0U, RegState::Debug);
+
+  MIB.addMetadata(MDPtr);
+
   return &*MIB;
 }
 
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 2a1ded04b4..e9bafc9242 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -4422,11 +4422,15 @@ SelectionDAGBuilder::EmitFuncArgumentDbgValue(const Value *V, MDNode *Variable,
     return false;
 
   if (Op->isReg())
-    Op->setIsDebug();
-
-  FuncInfo.ArgDbgValues.push_back(
+    FuncInfo.ArgDbgValues.push_back(BuildMI(MF, getCurDebugLoc(),
+                                            TII->get(TargetOpcode::DBG_VALUE),
+                                            /* IsIndirect */ Offset != 0,
+                                            Op->getReg(), Offset, Variable));
+  else
+    FuncInfo.ArgDbgValues.push_back(
       BuildMI(MF, getCurDebugLoc(), TII->get(TargetOpcode::DBG_VALUE))
           .addOperand(*Op).addImm(Offset).addMetadata(Variable));
+
   return true;
 }
 
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 3d490fac6b..98879649c8 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -421,12 +421,13 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
       MachineBasicBlock::iterator InsertPos = Def;
       const MDNode *Variable =
         MI->getOperand(MI->getNumOperands()-1).getMetadata();
-      unsigned Offset = MI->getOperand(1).getImm();
+      bool IsIndirect = MI->getOperand(1).isImm();
+      unsigned Offset = IsIndirect ? MI->getOperand(1).getImm() : 0;
       // Def is never a terminator here, so it is ok to increment InsertPos.
       BuildMI(*EntryMBB, ++InsertPos, MI->getDebugLoc(),
-              TII.get(TargetOpcode::DBG_VALUE))
-        .addReg(LDI->second, RegState::Debug)
-        .addImm(Offset).addMetadata(Variable);
+              TII.get(TargetOpcode::DBG_VALUE),
+              IsIndirect,
+              LDI->second, Offset, Variable);
 
       // If this vreg is directly copied into an exported register then
       // that COPY instructions also need DBG_VALUE, if it is the only
@@ -445,9 +446,10 @@ bool SelectionDAGISel::runOnMachineFunction(MachineFunction &mf) {
       if (CopyUseMI) {
         MachineInstr *NewMI =
           BuildMI(*MF, CopyUseMI->getDebugLoc(),
-                  TII.get(TargetOpcode::DBG_VALUE))
-          .addReg(CopyUseMI->getOperand(0).getReg(), RegState::Debug)
-          .addImm(Offset).addMetadata(Variable);
+                  TII.get(TargetOpcode::DBG_VALUE),
+                  IsIndirect,
+                  CopyUseMI->getOperand(0).getReg(),
+                  Offset, Variable);
         MachineBasicBlock::iterator Pos = CopyUseMI;
         EntryMBB->insertAfter(Pos, NewMI);
       }
diff --git a/test/CodeGen/X86/dbg-value-range.ll b/test/CodeGen/X86/dbg-value-range.ll
index b068bbbe78..83aa34e8a4 100644
--- a/test/CodeGen/X86/dbg-value-range.ll
+++ b/test/CodeGen/X86/dbg-value-range.ll
@@ -40,7 +40,7 @@ declare void @llvm.dbg.value(metadata, i64, metadata) nounwind readnone
 !21 = metadata !{metadata !6, metadata !11}
 !22 = metadata !{metadata !"bar.c", metadata !"/private/tmp"}
 
-; Check that variable bar:b value range is appropriately trucated in debug info.
+; Check that variable bar:b value range is appropriately truncated in debug info.
 ; The variable is in %rdi which is clobbered by 'movl %ebx, %edi'
 ; Here Ltmp7 is the end of the location range.
 
@@ -54,7 +54,7 @@ declare void @llvm.dbg.value(metadata, i64, metadata) nounwind readnone
 ;CHECK-NEXT: Lset{{.*}} = Ltmp{{.*}}-Ltmp{{.*}}
 ;CHECK-NEXT:    .short  Lset
 ;CHECK-NEXT: Ltmp
-;CHECK-NEXT:	.byte	85
+;CHECK-NEXT:	.byte	85 ## DW_OP_reg
 ;CHECK-NEXT: Ltmp
 ;CHECK-NEXT:	.quad	0
 ;CHECK-NEXT:	.quad	0
diff --git a/test/DebugInfo/X86/op_deref.ll b/test/DebugInfo/X86/op_deref.ll
index c3580a790c..fc9aab16ea 100644
--- a/test/DebugInfo/X86/op_deref.ll
+++ b/test/DebugInfo/X86/op_deref.ll
@@ -1,10 +1,16 @@
 ; RUN: llc -O0 -mtriple=x86_64-apple-darwin %s -o %t -filetype=obj
-; RUN: llvm-dwarfdump -debug-dump=info %t | FileCheck %s
+; RUN: llvm-dwarfdump -debug-dump=info %t | FileCheck %s -check-prefix=DW-CHECK
 
-; CHECK: DW_AT_name [DW_FORM_strp]  ( .debug_str[0x00000067] = "vla")
+; DW-CHECK: DW_AT_name [DW_FORM_strp]  ( .debug_str[0x00000067] = "vla")
 ; FIXME: The location here needs to be fixed, but llvm-dwarfdump doesn't handle
 ; DW_AT_location lists yet.
-; CHECK: DW_AT_location [DW_FORM_data4]                      (0x00000000)
+; DW-CHECK: DW_AT_location [DW_FORM_data4]                      (0x00000000)
+
+; Unfortunately llvm-dwarfdump can't unparse a list of DW_AT_locations
+; right now, so we check the asm output:
+; RUN: llc -O0 -mtriple=x86_64-apple-darwin %s -o - -filetype=asm | FileCheck %s -check-prefix=ASM-CHECK
+; vla should have a register-indirect address at one point.
+; ASM-CHECK: DEBUG_VALUE: vla <- [RCX+0]
 
 define void @testVLAwithSize(i32 %s) nounwind uwtable ssp {
 entry:
diff --git a/test/DebugInfo/X86/parameters.ll b/test/DebugInfo/X86/parameters.ll
index 6834f4b0d2..78469243b3 100644
--- a/test/DebugInfo/X86/parameters.ll
+++ b/test/DebugInfo/X86/parameters.ll
@@ -24,9 +24,9 @@
 
 ; CHECK: debug_info contents
 ; CHECK: DW_AT_name{{.*}} = "f"
-; 0x74 is DW_OP_breg0 + 4, showing that the parameter is accessed indirectly
+; 0x74 is DW_OP_breg4, showing that the parameter is accessed indirectly
 ; (with a zero offset) from the register parameter
-; CHECK: DW_AT_location{{.*}}(<0x02> 74 00 )
+; CHECK: DW_AT_location{{.*}}(<0x0{{.}}> 74 00
 
 ; CHECK: DW_AT_name{{.*}} = "g"
 ; CHECK: DW_AT_location{{.*}}([[G_LOC:0x[0-9]*]])
diff --git a/test/DebugInfo/X86/vla.ll b/test/DebugInfo/X86/vla.ll
new file mode 100644
index 0000000000..81faec70b7
--- /dev/null
+++ b/test/DebugInfo/X86/vla.ll
@@ -0,0 +1,104 @@
+; RUN: llc -O0 -mtriple=x86_64-apple-darwin -filetype=asm %s -o - | FileCheck %s
+; Ensure that we generate a breg+0 location for the variable length array a.
+; CHECK: ##DEBUG_VALUE: vla:a <- [RDX+0]
+; rdar://problem/13658587
+;
+; generated from:
+;
+; int vla(int n) {
+;   int a[n];
+;   a[0] = 42;
+;   return a[n-1];
+; }
+;
+; int main(int argc, char** argv) {
+;    return vla(argc);
+; }
+
+; ModuleID = 'vla.c'
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.8.0"
+
+; Function Attrs: nounwind ssp uwtable
+define i32 @vla(i32 %n) nounwind ssp uwtable {
+entry:
+  %n.addr = alloca i32, align 4
+  %saved_stack = alloca i8*
+  %cleanup.dest.slot = alloca i32
+  store i32 %n, i32* %n.addr, align 4
+  call void @llvm.dbg.declare(metadata !{i32* %n.addr}, metadata !15), !dbg !16
+  %0 = load i32* %n.addr, align 4, !dbg !17
+  %1 = zext i32 %0 to i64, !dbg !17
+  %2 = call i8* @llvm.stacksave(), !dbg !17
+  store i8* %2, i8** %saved_stack, !dbg !17
+  %vla = alloca i32, i64 %1, align 16, !dbg !17
+  call void @llvm.dbg.declare(metadata !{i32* %vla}, metadata !18), !dbg !17
+  %arrayidx = getelementptr inbounds i32* %vla, i64 0, !dbg !22
+  store i32 42, i32* %arrayidx, align 4, !dbg !22
+  %3 = load i32* %n.addr, align 4, !dbg !23
+  %sub = sub nsw i32 %3, 1, !dbg !23
+  %idxprom = sext i32 %sub to i64, !dbg !23
+  %arrayidx1 = getelementptr inbounds i32* %vla, i64 %idxprom, !dbg !23
+  %4 = load i32* %arrayidx1, align 4, !dbg !23
+  store i32 1, i32* %cleanup.dest.slot
+  %5 = load i8** %saved_stack, !dbg !24
+  call void @llvm.stackrestore(i8* %5), !dbg !24
+  ret i32 %4, !dbg !23
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone
+
+; Function Attrs: nounwind
+declare i8* @llvm.stacksave() nounwind
+
+; Function Attrs: nounwind
+declare void @llvm.stackrestore(i8*) nounwind
+
+; Function Attrs: nounwind ssp uwtable
+define i32 @main(i32 %argc, i8** %argv) nounwind ssp uwtable {
+entry:
+  %retval = alloca i32, align 4
+  %argc.addr = alloca i32, align 4
+  %argv.addr = alloca i8**, align 8
+  store i32 0, i32* %retval
+  store i32 %argc, i32* %argc.addr, align 4
+  call void @llvm.dbg.declare(metadata !{i32* %argc.addr}, metadata !25), !dbg !26
+  store i8** %argv, i8*** %argv.addr, align 8
+  call void @llvm.dbg.declare(metadata !{i8*** %argv.addr}, metadata !27), !dbg !26
+  %0 = load i32* %argc.addr, align 4, !dbg !28
+  %call = call i32 @vla(i32 %0), !dbg !28
+  ret i32 %call, !dbg !28
+}
+
+!llvm.dbg.cu = !{!0}
+
+!0 = metadata !{i32 786449, metadata !1, i32 12, metadata !"clang version 3.3 ", i1 false, metadata !"", i32 0, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2, metadata !""} ; [ DW_TAG_compile_unit ] [/vla.c] [DW_LANG_C99]
+!1 = metadata !{metadata !"vla.c", metadata !""}
+!2 = metadata !{i32 0}
+!3 = metadata !{metadata !4, metadata !9}
+!4 = metadata !{i32 786478, metadata !1, metadata !5, metadata !"vla", metadata !"vla", metadata !"", i32 1, metadata !6, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 false, i32 (i32)* @vla, null, null, metadata !2, i32 1} ; [ DW_TAG_subprogram ] [line 1] [def] [vla]
+!5 = metadata !{i32 786473, metadata !1}          ; [ DW_TAG_file_type ] [/vla.c]
+!6 = metadata !{i32 786453, i32 0, i32 0, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !7, i32 0, i32 0} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!7 = metadata !{metadata !8, metadata !8}
+!8 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32, align 32, offset 0, enc DW_ATE_signed]
+!9 = metadata !{i32 786478, metadata !1, metadata !5, metadata !"main", metadata !"main", metadata !"", i32 7, metadata !10, i1 false, i1 true, i32 0, i32 0, null, i32 256, i1 false, i32 (i32, i8**)* @main, null, null, metadata !2, i32 7} ; [ DW_TAG_subprogram ] [line 7] [def] [main]
+!10 = metadata !{i32 786453, i32 0, i32 0, metadata !"", i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !11, i32 0, i32 0} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!11 = metadata !{metadata !8, metadata !8, metadata !12}
+!12 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 0, metadata !13} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from ]
+!13 = metadata !{i32 786447, null, null, metadata !"", i32 0, i64 64, i64 64, i64 0, i32 0, metadata !14} ; [ DW_TAG_pointer_type ] [line 0, size 64, align 64, offset 0] [from char]
+!14 = metadata !{i32 786468, null, null, metadata !"char", i32 0, i64 8, i64 8, i64 0, i32 0, i32 6} ; [ DW_TAG_base_type ] [char] [line 0, size 8, align 8, offset 0, enc DW_ATE_signed_char]
+!15 = metadata !{i32 786689, metadata !4, metadata !"n", metadata !5, i32 16777217, metadata !8, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [n] [line 1]
+!16 = metadata !{i32 1, i32 0, metadata !4, null}
+!17 = metadata !{i32 2, i32 0, metadata !4, null}
+!18 = metadata !{i32 786688, metadata !4, metadata !"a", metadata !5, i32 2, metadata !19, i32 0, i32 0} ; [ DW_TAG_auto_variable ] [a] [line 2]
+!19 = metadata !{i32 786433, null, null, metadata !"", i32 0, i64 0, i64 32, i32 0, i32 0, metadata !8, metadata !20, i32 0, i32 0} ; [ DW_TAG_array_type ] [line 0, size 0, align 32, offset 0] [from int]
+!20 = metadata !{metadata !21}
+!21 = metadata !{i32 786465, i64 0, i64 -1}       ; [ DW_TAG_subrange_type ] [unbounded]
+!22 = metadata !{i32 3, i32 0, metadata !4, null}
+!23 = metadata !{i32 4, i32 0, metadata !4, null}
+!24 = metadata !{i32 5, i32 0, metadata !4, null}
+!25 = metadata !{i32 786689, metadata !9, metadata !"argc", metadata !5, i32 16777223, metadata !8, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [argc] [line 7]
+!26 = metadata !{i32 7, i32 0, metadata !9, null}
+!27 = metadata !{i32 786689, metadata !9, metadata !"argv", metadata !5, i32 33554439, metadata !12, i32 0, i32 0} ; [ DW_TAG_arg_variable ] [argv] [line 7]
+!28 = metadata !{i32 8, i32 0, metadata !9, null}