[lldb/DWARF] Add support for DW_OP_implicit_value

This patch completes https://reviews.llvm.org/D83560. Now that the
compiler can emit `DW_OP_implicit_value` into DWARF expressions, lldb
needed to learn reading these opcodes for variable inspection and
expression evaluation.

This implicit location descriptor specifies an immediate value with two
operands: the length (ULEB128) followed by a block representing the value
in the target memory representation.

rdar://67406091

Differential revision: https://reviews.llvm.org/D89842

Signed-off-by: Med Ismail Bennani <[email protected]>

Author: medismailben

lldb/source/Expression/DWARFExpression.cpp

@@ -2248,6 +2248,29 @@ bool DWARFExpression::Evaluate(
       }
       break;
 
+    // OPCODE: DW_OP_implicit_value
+    // OPERANDS: 2
+    //      ULEB128  size of the value block in bytes
+    //      uint8_t* block bytes encoding value in target's memory
+    //      representation
+    // DESCRIPTION: Value is immediately stored in block in the debug info with
+    // the memory representation of the target.
+    case DW_OP_implicit_value: {
+      const uint32_t len = opcodes.GetULEB128(&offset);
+      const void *data = opcodes.GetData(&offset, len);
+
+      if (!data) {
+        LLDB_LOG(log, "Evaluate_DW_OP_implicit_value: could not be read data");
+        LLDB_ERRORF(error_ptr, "Could not evaluate %s.",
+                    DW_OP_value_to_name(op));
+        return false;
+      }
+
+      Value result(data, len);
+      stack.push_back(result);
+      break;
+    }
+
     // OPCODE: DW_OP_push_object_address
     // OPERANDS: none
     // DESCRIPTION: Pushes the address of the object currently being

lldb/unittests/Expression/DWARFExpressionTest.cpp

@@ -218,6 +218,14 @@ TEST(DWARFExpression, DW_OP_piece) {
       llvm::HasValue(GetScalar(16, 0xff00, true)));
 }
 
+TEST(DWARFExpression, DW_OP_implicit_value) {
+  unsigned char bytes = 4;
+
+  EXPECT_THAT_EXPECTED(
+      Evaluate({DW_OP_implicit_value, bytes, 0x11, 0x22, 0x33, 0x44}),
+      llvm::HasValue(GetScalar(8 * bytes, 0x44332211, true)));
+}
+
 TEST(DWARFExpression, DW_OP_unknown) {
   EXPECT_THAT_EXPECTED(
       Evaluate({0xff}),