[Local] replaceAllDbgUsesWith: Update debug values before RAUW

The replaceAllDbgUsesWith utility helps passes preserve debug info when
replacing one value with another.

This improves upon the existing insertReplacementDbgValues API by:

- Updating debug intrinsics in-place, while preventing use-before-def of
  the replacement value.
- Falling back to salvageDebugInfo when a replacement can't be made.
- Moving the responsibiliy for rewriting llvm.dbg.* DIExpressions into
  common utility code.

Along with the API change, this teaches replaceAllDbgUsesWith how to
create DIExpressions for three basic integer and pointer conversions:

- The no-op conversion. Applies when the values have the same width, or
  have bit-for-bit compatible pointer representations.
- Truncation. Applies when the new value is wider than the old one.
- Zero/sign extension. Applies when the new value is narrower than the
  old one.

Testing:

- check-llvm, check-clang, a stage2 `-g -O3` build of clang,
  regression/unit testing.
- This resolves a number of mis-sized dbg.value diagnostics from
  Debugify.

Differential Revision: https://reviews.llvm.org/D48676

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@336451 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 52 insertions, 0 deletions

diff --git a/lib/IR/DebugInfoMetadata.cpp b/lib/IR/DebugInfoMetadata.cpp
index 5d9e3405880..0124980485d 100644
--- a/lib/IR/DebugInfoMetadata.cpp
+++ b/lib/IR/DebugInfoMetadata.cpp
@@ -283,6 +283,19 @@ DIBasicType *DIBasicType::getImpl(LLVMContext &Context, unsigned Tag,
                        Ops);
 }
 
+Optional<DIBasicType::Signedness> DIBasicType::getSignedness() const {
+  switch (getEncoding()) {
+  case dwarf::DW_ATE_signed:
+  case dwarf::DW_ATE_signed_char:
+    return Signedness::Signed;
+  case dwarf::DW_ATE_unsigned:
+  case dwarf::DW_ATE_unsigned_char:
+    return Signedness::Unsigned;
+  default:
+    return None;
+  }
+}
+
 DIDerivedType *DIDerivedType::getImpl(
     LLVMContext &Context, unsigned Tag, MDString *Name, Metadata *File,
     unsigned Line, Metadata *Scope, Metadata *BaseType, uint64_t SizeInBits,
@@ -733,6 +746,9 @@ bool DIExpression::isValid() const {
     case dwarf::DW_OP_shra:
     case dwarf::DW_OP_deref:
     case dwarf::DW_OP_xderef:
+    case dwarf::DW_OP_lit0:
+    case dwarf::DW_OP_not:
+    case dwarf::DW_OP_dup:
       break;
     }
   }
@@ -826,6 +842,42 @@ DIExpression *DIExpression::prependOpcodes(const DIExpression *Expr,
   return DIExpression::get(Expr->getContext(), Ops);
 }
 
+DIExpression *DIExpression::appendToStack(const DIExpression *Expr,
+                                          ArrayRef<uint64_t> Ops) {
+  assert(Expr && !Ops.empty() && "Can't append ops to this expression");
+
+  // Append a DW_OP_deref after Expr's current op list if it's non-empty and
+  // has no DW_OP_stack_value.
+  //
+  // Match .* DW_OP_stack_value (DW_OP_LLVM_fragment A B)?.
+  Optional<FragmentInfo> FI = Expr->getFragmentInfo();
+  unsigned DropUntilStackValue = FI.hasValue() ? 3 : 0;
+  bool NeedsDeref =
+      (Expr->getNumElements() > DropUntilStackValue) &&
+      (Expr->getElements().drop_back(DropUntilStackValue).back() !=
+       dwarf::DW_OP_stack_value);
+
+  // Copy Expr's current op list, add a DW_OP_deref if needed, and ensure that
+  // a DW_OP_stack_value is present.
+  SmallVector<uint64_t, 16> NewOps;
+  for (auto Op : Expr->expr_ops()) {
+    if (Op.getOp() == dwarf::DW_OP_stack_value ||
+        Op.getOp() == dwarf::DW_OP_LLVM_fragment)
+      break;
+    Op.appendToVector(NewOps);
+  }
+  if (NeedsDeref)
+    NewOps.push_back(dwarf::DW_OP_deref);
+  NewOps.append(Ops.begin(), Ops.end());
+  NewOps.push_back(dwarf::DW_OP_stack_value);
+
+  // If Expr is a fragment, make the new expression a fragment as well.
+  if (FI)
+    NewOps.append(
+        {dwarf::DW_OP_LLVM_fragment, FI->OffsetInBits, FI->SizeInBits});
+  return DIExpression::get(Expr->getContext(), NewOps);
+}
+
 Optional<DIExpression *> DIExpression::createFragmentExpression(
     const DIExpression *Expr, unsigned OffsetInBits, unsigned SizeInBits) {
   SmallVector<uint64_t, 8> Ops;