[DwarfExpression] Support entry values for indirect parameters

Summary:
A struct argument can be passed-by-value to a callee via a pointer to a
temporary stack copy. Add support for emitting an entry value DBG_VALUE
when an indirect parameter DBG_VALUE becomes unavailable. This is done
by omitting DW_OP_stack_value from the entry value expression, to make
the expression describe the location of an object.

rdar://63373691

Reviewers: djtodoro, aprantl, dstenb

Subscribers: hiraditya, lldb-commits, llvm-commits

Tags: #lldb, #llvm

Differential Revision: https://reviews.llvm.org/D80345

5 files changed, 37 insertions, 20 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index 93bf9d6..dce90b3 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -1285,15 +1285,12 @@ void DwarfCompileUnit::addComplexAddress(const DbgVariable &DV, DIE &Die,
   DIEDwarfExpression DwarfExpr(*Asm, *this, *Loc);
   const DIExpression *DIExpr = DV.getSingleExpression();
   DwarfExpr.addFragmentOffset(DIExpr);
-  if (Location.isIndirect())
-    DwarfExpr.setMemoryLocationKind();
+  DwarfExpr.setLocation(Location, DIExpr);
 
   DIExpressionCursor Cursor(DIExpr);
 
-  if (DIExpr->isEntryValue()) {
-    DwarfExpr.setEntryValueFlag();
+  if (DIExpr->isEntryValue())
     DwarfExpr.beginEntryValueExpression(Cursor);
-  }
 
   const TargetRegisterInfo &TRI = *Asm->MF->getSubtarget().getRegisterInfo();
   if (!DwarfExpr.addMachineRegExpression(TRI, Cursor, Location.getReg()))
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 17fcf69..953154f 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -2399,14 +2399,11 @@ void DwarfDebug::emitDebugLocValue(const AsmPrinter &AP, const DIBasicType *BT,
       DwarfExpr.addUnsignedConstant(Value.getInt());
   } else if (Value.isLocation()) {
     MachineLocation Location = Value.getLoc();
-    if (Location.isIndirect())
-      DwarfExpr.setMemoryLocationKind();
+    DwarfExpr.setLocation(Location, DIExpr);
     DIExpressionCursor Cursor(DIExpr);
 
-    if (DIExpr->isEntryValue()) {
-      DwarfExpr.setEntryValueFlag();
+    if (DIExpr->isEntryValue())
       DwarfExpr.beginEntryValueExpression(Cursor);
-    }
 
     const TargetRegisterInfo &TRI = *AP.MF->getSubtarget().getRegisterInfo();
     if (!DwarfExpr.addMachineRegExpression(TRI, Cursor, Location.getReg()))
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
index 69bc06c..7b64c22 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -259,7 +259,8 @@ bool DwarfExpression::addMachineRegExpression(const TargetRegisterInfo &TRI,
     if (isEntryValue())
       finalizeEntryValue();
 
-    if (isEntryValue() && !isParameterValue() && DwarfVersion >= 4)
+    if (isEntryValue() && !isIndirect() && !isParameterValue() &&
+        DwarfVersion >= 4)
       emitOp(dwarf::DW_OP_stack_value);
 
     DwarfRegs.clear();
@@ -318,6 +319,25 @@ bool DwarfExpression::addMachineRegExpression(const TargetRegisterInfo &TRI,
   return true;
 }
 
+void DwarfExpression::setEntryValueFlags(const MachineLocation &Loc) {
+  LocationFlags |= EntryValue;
+  if (Loc.isIndirect())
+    LocationFlags |= Indirect;
+}
+
+void DwarfExpression::setLocation(const MachineLocation &Loc,
+                                  const DIExpression *DIExpr) {
+  if (Loc.isIndirect())
+    // Do not treat entry value descriptions of indirect parameters as memory
+    // locations. This allows DwarfExpression::addReg() to add DW_OP_regN to an
+    // entry value description.
+    if (!DIExpr->isEntryValue())
+      setMemoryLocationKind();
+
+  if (DIExpr->isEntryValue())
+    setEntryValueFlags(Loc);
+}
+
 void DwarfExpression::beginEntryValueExpression(
     DIExpressionCursor &ExprCursor) {
   auto Op = ExprCursor.take();
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
index 5d43862..42be827 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
@@ -30,6 +30,7 @@ class APInt;
 class DwarfCompileUnit;
 class DIELoc;
 class TargetRegisterInfo;
+class MachineLocation;
 
 /// Holds a DIExpression and keeps track of how many operands have been consumed
 /// so far.
@@ -142,14 +143,18 @@ protected:
   /// The kind of location description being produced.
   enum { Unknown = 0, Register, Memory, Implicit };
 
-  /// The flags of location description being produced.
-  enum { EntryValue = 1, CallSiteParamValue };
+  /// Additional location flags which may be combined with any location kind.
+  /// Currently, entry values are not supported for the Memory location kind.
+  enum { EntryValue = 1 << 0, Indirect = 1 << 1, CallSiteParamValue = 1 << 2 };
 
   unsigned LocationKind : 3;
-  unsigned LocationFlags : 2;
+  unsigned LocationFlags : 3;
   unsigned DwarfVersion : 4;
 
 public:
+  /// Set the location (\p Loc) and \ref DIExpression (\p DIExpr) to describe.
+  void setLocation(const MachineLocation &Loc, const DIExpression *DIExpr);
+
   bool isUnknownLocation() const { return LocationKind == Unknown; }
 
   bool isMemoryLocation() const { return LocationKind == Memory; }
@@ -160,6 +165,8 @@ public:
 
   bool isEntryValue() const { return LocationFlags & EntryValue; }
 
+  bool isIndirect() const { return LocationFlags & Indirect; }
+
   bool isParameterValue() { return LocationFlags & CallSiteParamValue; }
 
   Optional<uint8_t> TagOffset;
@@ -296,7 +303,7 @@ public:
   }
 
   /// Lock this down to become an entry value location.
-  void setEntryValueFlag() { LocationFlags |= EntryValue; }
+  void setEntryValueFlags(const MachineLocation &Loc);
 
   /// Lock this down to become a call site parameter location.
   void setCallSiteParamValueFlag() { LocationFlags |= CallSiteParamValue; }
diff --git a/llvm/lib/CodeGen/LiveDebugValues.cpp b/llvm/lib/CodeGen/LiveDebugValues.cpp
index 470cb22..00a6149a 100644
--- a/llvm/lib/CodeGen/LiveDebugValues.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues.cpp
@@ -1613,10 +1613,6 @@ bool LiveDebugValues::isEntryValueCandidate(
   if (MI.getDebugLoc()->getInlinedAt())
     return false;
 
-  // Do not consider indirect debug values (TODO: explain why).
-  if (MI.isIndirectDebugValue())
-    return false;
-
   // Only consider parameters that are described using registers. Parameters
   // that are passed on the stack are not yet supported, so ignore debug
   // values that are described by the frame or stack pointer.
@@ -1631,7 +1627,7 @@ bool LiveDebugValues::isEntryValueCandidate(
     return false;
 
   // TODO: Add support for parameters that have a pre-existing debug expressions
-  // (e.g. fragments, or indirect parameters using DW_OP_deref).
+  // (e.g. fragments).
   if (MI.getDebugExpression()->getNumElements() > 0)
     return false;