Reland r311957 [codeview] support more DW_OPs for more complete debug info

Summary:
Some variables show up in Visual Studio as "optimized out" even in -O0
-Od builds. This change fixes two issues that would cause this to
happen. The first issue is that not all DIExpressions we generate were
recognized by the CodeView writer. This has been addressed by adding
support for DW_OP_constu, DW_OP_minus, and DW_OP_plus. The second
issue is that we had no way to encode DW_OP_deref in CodeView. We get
around that by changinge the type we encode in the debug info to be
a reference to the type in the source code.

This fixes PR34261.

The reland adds two extra checks to the original: It checks if the
DbgVariableLocation is valid before checking any of its fields, and
it only emits ranges with nonzero registers.

Reviewers: aprantl, rnk, zturner

Reviewed By: rnk

Subscribers: mgorny, llvm-commits, aprantl, hiraditya

Differential Revision: https://reviews.llvm.org/D36907

llvm-svn: 312034

1 files changed, 51 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
index 0971c594220..4f647de1ed2 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
@@ -23,6 +23,57 @@
 
 using namespace llvm;
 
+bool DbgVariableLocation::extractFromMachineInstruction(
+    DbgVariableLocation &Location, const MachineInstr &Instruction) {
+  if (!Instruction.isDebugValue())
+    return false;
+  if (!Instruction.getOperand(0).isReg())
+    return false;
+  Location.Register = Instruction.getOperand(0).getReg();
+  Location.InMemory = Instruction.getOperand(1).isImm();
+  Location.Deref = false;
+  Location.FragmentInfo.reset();
+  // We only handle expressions generated by DIExpression::appendOffset,
+  // which doesn't require a full stack machine.
+  int64_t Offset = 0;
+  const DIExpression *DIExpr = Instruction.getDebugExpression();
+  auto Op = DIExpr->expr_op_begin();
+  while (Op != DIExpr->expr_op_end()) {
+    switch (Op->getOp()) {
+    case dwarf::DW_OP_constu: {
+      int Value = Op->getArg(0);
+      ++Op;
+      if (Op != DIExpr->expr_op_end()) {
+        switch (Op->getOp()) {
+        case dwarf::DW_OP_minus:
+          Offset -= Value;
+          break;
+        case dwarf::DW_OP_plus:
+          Offset += Value;
+        default:
+          continue;
+        }
+      }
+    } break;
+    case dwarf::DW_OP_plus_uconst:
+      Offset += Op->getArg(0);
+      break;
+    case dwarf::DW_OP_LLVM_fragment:
+      Location.FragmentInfo = {Op->getArg(1), Op->getArg(0)};
+      break;
+    case dwarf::DW_OP_deref:
+      Location.Deref = true;
+      break;
+    default:
+      return false;
+    }
+    ++Op;
+  }
+
+  Location.Offset = Offset;
+  return true;
+}
+
 DebugHandlerBase::DebugHandlerBase(AsmPrinter *A) : Asm(A), MMI(Asm->MMI) {}
 
 // Each LexicalScope has first instruction and last instruction to mark