[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

1 files changed, 15 insertions, 0 deletions

diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index 7158e5764fa..4ef38b6f7fe 100644
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -833,6 +833,7 @@ unsigned DIExpression::ExprOperand::getSize() const {
   case dwarf::DW_OP_LLVM_fragment:
     return 3;
   case dwarf::DW_OP_constu:
+  case dwarf::DW_OP_deref_size:
   case dwarf::DW_OP_plus_uconst:
     return 2;
   default:
@@ -889,6 +890,7 @@ bool DIExpression::isValid() const {
     case dwarf::DW_OP_shr:
     case dwarf::DW_OP_shra:
     case dwarf::DW_OP_deref:
+    case dwarf::DW_OP_deref_size:
     case dwarf::DW_OP_xderef:
     case dwarf::DW_OP_lit0:
     case dwarf::DW_OP_not:
@@ -899,6 +901,19 @@ bool DIExpression::isValid() const {
   return true;
 }
 
+bool DIExpression::isImplicit() const {
+  unsigned N = getNumElements();
+  if (isValid() && N > 0) {
+    switch (getElement(N-1)) {
+      case dwarf::DW_OP_stack_value: return true;
+      case dwarf::DW_OP_LLVM_fragment:
+        return N > 1 && getElement(N-2) == dwarf::DW_OP_stack_value;
+      default: break;
+    }
+  }
+  return false;
+}
+
 Optional<DIExpression::FragmentInfo>
 DIExpression::getFragmentInfo(expr_op_iterator Start, expr_op_iterator End) {
   for (auto I = Start; I != End; ++I)