[DebugInfo] DW_OP_deref_size in PrologEpilogInserter.

The PrologEpilogInserter need to insert a DW_OP_deref_size before
prepending a memory location expression to an already implicit
expression to avoid having the existing expression act on the memory
address instead of the value behind it.

The reason for using DW_OP_deref_size and not plain DW_OP_deref is that
big-endian targets need to read the right size as simply truncating a
larger read would yield the wrong result (LSB bytes are not at the lower
address).

This re-commit fixes issues reported in the first one. Namely deref was
inserted under wrong conditions and additionally the deref_size argument
was incorrectly encoded.

Differential Revision: https://reviews.llvm.org/D59687

llvm-svn: 359535

6 files changed, 38 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index e31b1e5c3ad..c3dad62f386 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -179,6 +179,10 @@ void DebugLocDwarfExpression::emitUnsigned(uint64_t Value) {
   BS.EmitULEB128(Value, Twine(Value));
 }
 
+void DebugLocDwarfExpression::emitData1(uint8_t Value) {
+  BS.EmitInt8(Value, Twine(Value));
+}
+
 void DebugLocDwarfExpression::emitBaseTypeRef(uint64_t Idx) {
   assert(Idx < (1ULL << (ULEB128PadSize * 7)) && "Idx wont fit");
   BS.EmitULEB128(Idx, Twine(Idx), ULEB128PadSize);
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
index 41fa45f2507..1235c149005 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
@@ -434,6 +434,10 @@ void DwarfExpression::addExpression(DIExpressionCursor &&ExprCursor,
       assert(LocationKind != Register);
       emitOp(dwarf::DW_OP_xderef);
       break;
+    case dwarf::DW_OP_deref_size:
+      emitOp(dwarf::DW_OP_deref_size);
+      emitData1(Op->getArg(0));
+      break;
     default:
       llvm_unreachable("unhandled opcode found in expression");
     }
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
index 18bedf0b902..145504946a5 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.h
@@ -139,6 +139,8 @@ protected:
   /// Emit a raw unsigned value.
   virtual void emitUnsigned(uint64_t Value) = 0;
 
+  virtual void emitData1(uint8_t Value) = 0;
+
   virtual void emitBaseTypeRef(uint64_t Idx) = 0;
 
   /// Emit a normalized unsigned constant.
@@ -264,6 +266,7 @@ class DebugLocDwarfExpression final : public DwarfExpression {
   void emitOp(uint8_t Op, const char *Comment = nullptr) override;
   void emitSigned(int64_t Value) override;
   void emitUnsigned(uint64_t Value) override;
+  void emitData1(uint8_t Value) override;
   void emitBaseTypeRef(uint64_t Idx) override;
   bool isFrameRegister(const TargetRegisterInfo &TRI,
                        unsigned MachineReg) override;
@@ -281,6 +284,7 @@ const AsmPrinter &AP;
   void emitOp(uint8_t Op, const char *Comment = nullptr) override;
   void emitSigned(int64_t Value) override;
   void emitUnsigned(uint64_t Value) override;
+  void emitData1(uint8_t Value) override;
   void emitBaseTypeRef(uint64_t Idx) override;
   bool isFrameRegister(const TargetRegisterInfo &TRI,
                        unsigned MachineReg) override;
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
index cace8f06992..6b641eafc44 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -64,6 +64,10 @@ void DIEDwarfExpression::emitUnsigned(uint64_t Value) {
   CU.addUInt(DIE, dwarf::DW_FORM_udata, Value);
 }
 
+void DIEDwarfExpression::emitData1(uint8_t Value) {
+  CU.addUInt(DIE, dwarf::DW_FORM_data1, Value);
+}
+
 void DIEDwarfExpression::emitBaseTypeRef(uint64_t Idx) {
   CU.addBaseTypeRef(DIE, Idx);
 }
diff --git a/llvm/lib/CodeGen/MIRParser/MIParser.cpp b/llvm/lib/CodeGen/MIRParser/MIParser.cpp
index 971944be2f9..d414b6a0b4b 100644
--- a/llvm/lib/CodeGen/MIRParser/MIParser.cpp
+++ b/llvm/lib/CodeGen/MIRParser/MIParser.cpp
@@ -1854,6 +1854,11 @@ bool MIParser::parseDIExpression(MDNode *&Expr) {
           Elements.push_back(Op);
           continue;
         }
+        if (unsigned Enc = dwarf::getAttributeEncoding(Token.stringValue())) {
+          lex();
+          Elements.push_back(Enc);
+          continue;
+        }
         return error(Twine("invalid DWARF op '") + Token.stringValue() + "'");
       }
 
diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index 67834c8c352..55925c8cf45 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -1172,12 +1172,26 @@ void PEI::replaceFrameIndices(MachineBasicBlock *BB, MachineFunction &MF,
         assert(i == 0 && "Frame indices can only appear as the first "
                          "operand of a DBG_VALUE machine instruction");
         unsigned Reg;
+        unsigned FrameIdx = MI.getOperand(0).getIndex();
+        unsigned Size = MF.getFrameInfo().getObjectSize(FrameIdx);
+
         int64_t Offset =
-            TFI->getFrameIndexReference(MF, MI.getOperand(0).getIndex(), Reg);
+            TFI->getFrameIndexReference(MF, FrameIdx, Reg);
         MI.getOperand(0).ChangeToRegister(Reg, false /*isDef*/);
         MI.getOperand(0).setIsDebug();
-        auto *DIExpr = DIExpression::prepend(MI.getDebugExpression(),
-                                             DIExpression::NoDeref, Offset);
+
+        const DIExpression *DIExpr = MI.getDebugExpression();
+        // If we have DBG_VALUE that is indirect and has a Implicit location
+        // expression need to insert a deref before prepending a Memory
+        // location expression. Also after doing this we change the DBG_VALUE
+        // to be direct.
+        if (MI.isIndirectDebugValue() && DIExpr->isImplicit()) {
+          SmallVector<uint64_t, 2> Ops = {dwarf::DW_OP_deref_size, Size};
+          DIExpr = DIExpression::prependOpcodes(DIExpr, Ops, DIExpression::WithStackValue);
+          // Make the DBG_VALUE direct.
+          MI.getOperand(1).ChangeToRegister(0, false);
+        }
+        DIExpr = DIExpression::prepend(DIExpr, DIExpression::NoDeref, Offset);
         MI.getOperand(3).setMetadata(DIExpr);
         continue;
       }