[llvm-objdump] Add entry_value locations to variable display

[ostannard]

Summary

This adds the DW_OP_entry_value and DW_OP_stack_value opcodes to the DWARF expression printer, needed to display variable locations which refer to the value of an expression at entry to the function.

[aprantl]

llvm/test/tools/llvm-objdump/ARM/debug-vars-entry-value.s

1 ↗

(On Diff #245422)

It would be a lot more efficient to test this in unittests/DebugInfo/dwarf, but just dumping the expression bytes themselves. Otherwise the canonical place to test dwarf dumping facilities is usually llvm-dwarfdump.

I'm kind of worried that this test will need to be updated every time someone tunes the output formatting of objdump

[jhenderson]

llvm/test/tools/llvm-objdump/ARM/debug-vars-entry-value.s

1 ↗

(On Diff #245422)

+1 to this. The prettyPrint function looks ripe for gtest unit testing. I wouldn't necessarily worry about covering every code path in the first instance, but you could work towards it that way.

[ostannard]

Convert tests to unit tests.

[aprantl]

llvm/test/tools/llvm-objdump/ARM/debug-vars-entry-value.s

1 ↗

(On Diff #245422)

I think this test should be deleted now, it doesn't add anything over the unit test, right?

llvm/unittests/DebugInfo/DWARF/DWARFExpressionCompactPrinterTest.cpp

108

Nice.

[ostannard]

• Delete old test

[jhenderson]

LGTM too.

llvm/include/llvm/DebugInfo/DWARF/DWARFExpression.h

class Operation &operator++() {
           !Op.extract(Expr->Data, Expr->AddressSize, Offset);
       return Op;
     }
 
     class Operation &operator*() {
       return Op;
     }
 
+    iterator skipBytes(uint64_t Add) {
+      return iterator(Expr, Op.EndOffset + Add);
+    }
+
     // Comparison operators are provided out of line.
     friend bool operator==(const iterator &, const iterator &);
   };
 
   DWARFExpression(DataExtractor Data, uint8_t AddressSize)
       : Data(Data), AddressSize(AddressSize) {
     assert(AddressSize == 8 || AddressSize == 4 || AddressSize == 2);
   }

llvm/lib/DebugInfo/DWARF/DWARFExpression.cpp

case dwarf::DW_OP_bregx: {
         return false;
       }
       raw_svector_ostream S(Stack.emplace_back().String);
       S << MRI.getName(*LLVMRegNum);
       if (Offset)
         S << format("%+" PRId64, Offset);
       break;
     }
+    case dwarf::DW_OP_entry_value:
+    case dwarf::DW_OP_GNU_entry_value: {
+      // DW_OP_entry_value contains a sub-expression which must be rendered
+      // separately.
+      uint64_t SubExprLength = Op.getRawOperand(0);
+      DWARFExpression::iterator SubExprEnd = I.skipBytes(SubExprLength);
+      ++I;
+      raw_svector_ostream S(Stack.emplace_back().String);
+      S << "entry(";
+      printCompactDWARFExpr(S, I, SubExprEnd, MRI);
+      S << ")";
+      I = SubExprEnd;
+      continue;
+    }
+    case dwarf::DW_OP_stack_value: {
+      // The top stack entry should be treated as the actual value of tne
+      // variable, rather than the address of the variable in memory.
+      assert(!Stack.empty());
+      Stack.back().Kind = PrintedExpr::Value;
+      break;
+    }
     default:
       if (Opcode >= dwarf::DW_OP_reg0 && Opcode <= dwarf::DW_OP_reg31) {
         // DW_OP_reg<N>: A register, with the register num implied by the
         // opcode. Printed as the plain register name.
         uint64_t DwarfRegNum = Opcode - dwarf::DW_OP_reg0;
         Optional<unsigned> LLVMRegNum = MRI.getLLVMRegNum(DwarfRegNum, false);
         if (!LLVMRegNum) {
           OS << "<unknown register " << DwarfRegNum << ">";

llvm/unittests/DebugInfo/DWARF/DWARFExpressionCompactPrinterTest.cpp

 
 TEST_F(DWARFExpressionCompactPrinterTest, Test_OP_breg0_negative) {
   TestExprPrinter({DW_OP_breg0, 0x70}, "[R0-16]");
 }
 
 TEST_F(DWARFExpressionCompactPrinterTest, Test_OP_bregx) {
   TestExprPrinter({DW_OP_bregx, 0x0d, 0x28}, "[SP+40]");
 }
+
+TEST_F(DWARFExpressionCompactPrinterTest, Test_OP_stack_value) {
+  TestExprPrinter({DW_OP_breg13, 0x04, DW_OP_stack_value}, "SP+4");
+}
+
+TEST_F(DWARFExpressionCompactPrinterTest, Test_OP_entry_value) {
+  TestExprPrinter({DW_OP_entry_value, 0x01, DW_OP_reg0, DW_OP_stack_value},
+                  "entry(R0)");
+}
+
+TEST_F(DWARFExpressionCompactPrinterTest, Test_OP_entry_value_mem) {
+  TestExprPrinter(
+      {DW_OP_entry_value, 0x02, DW_OP_breg13, 0x10, DW_OP_stack_value},
+      "entry([SP+16])");
+}