[DebugInfo][X86] Improve X86 Optimize LEAs handling of debug values.

This is a follow up to the fix in r298360 to improve the handling of debug
values when redundant LEAs are removed. The fix in r298360 effectively
discarded the debug values. This patch now attempts to preserve the debug
values by using the DWARF DW_OP_stack_value operation via prependDIExpr.

Moved functions appendOffset and prependDIExpr from Local.cpp to
DebugInfoMetadata.cpp and made them available as static member functions of
DIExpression.

Differential Revision: https://reviews.llvm.org/D31604

llvm-svn: 301630

1 files changed, 6 insertions, 47 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index d3002c5fb75..1b643c53fe6 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -1259,50 +1259,8 @@ void llvm::findDbgValues(SmallVectorImpl<DbgValueInst *> &DbgValues, Value *V) {
           DbgValues.push_back(DVI);
 }
 
-static void appendOffset(SmallVectorImpl<uint64_t> &Ops, int64_t Offset) {
-  if (Offset > 0) {
-    Ops.push_back(dwarf::DW_OP_plus);
-    Ops.push_back(Offset);
-  } else if (Offset < 0) {
-    Ops.push_back(dwarf::DW_OP_minus);
-    Ops.push_back(-Offset);
-  }
-}
-
 enum { WithStackValue = true };
 
-/// Prepend \p DIExpr with a deref and offset operation and optionally turn it
-/// into a stack value.
-static DIExpression *prependDIExpr(DIBuilder &Builder, DIExpression *DIExpr,
-                                   bool Deref, int64_t Offset = 0,
-                                   bool StackValue = false) {
-  if (!Deref && !Offset && !StackValue)
-    return DIExpr;
-
-  SmallVector<uint64_t, 8> Ops;
-  appendOffset(Ops, Offset);
-  if (Deref)
-    Ops.push_back(dwarf::DW_OP_deref);
-  if (DIExpr)
-    for (auto Op : DIExpr->expr_ops()) {
-      // A DW_OP_stack_value comes at the end, but before a DW_OP_LLVM_fragment.
-      if (StackValue) {
-        if (Op.getOp() == dwarf::DW_OP_stack_value)
-          StackValue = false;
-        else if (Op.getOp() == dwarf::DW_OP_LLVM_fragment) {
-          Ops.push_back(dwarf::DW_OP_stack_value);
-          StackValue = false;
-        }
-      }
-      Ops.push_back(Op.getOp());
-      for (unsigned I = 0; I < Op.getNumArgs(); ++I)
-        Ops.push_back(Op.getArg(I));
-    }
-  if (StackValue)
-    Ops.push_back(dwarf::DW_OP_stack_value);
-  return Builder.createExpression(Ops);
-}
-
 bool llvm::replaceDbgDeclare(Value *Address, Value *NewAddress,
                              Instruction *InsertBefore, DIBuilder &Builder,
                              bool Deref, int Offset) {
@@ -1314,7 +1272,7 @@ bool llvm::replaceDbgDeclare(Value *Address, Value *NewAddress,
   auto *DIExpr = DDI->getExpression();
   assert(DIVar && "Missing variable");
 
-  DIExpr = prependDIExpr(Builder, DIExpr, Deref, Offset);
+  DIExpr = DIExpression::prependDIExpr(Builder, DIExpr, Deref, Offset);
 
   // Insert llvm.dbg.declare immediately after the original alloca, and remove
   // old llvm.dbg.declare.
@@ -1348,7 +1306,7 @@ static void replaceOneDbgValueForAlloca(DbgValueInst *DVI, Value *NewAddress,
   if (Offset) {
     SmallVector<uint64_t, 4> Ops;
     Ops.push_back(dwarf::DW_OP_deref);
-    appendOffset(Ops, Offset);
+    DIExpression::appendOffset(Ops, Offset);
     Ops.append(DIExpr->elements_begin() + 1, DIExpr->elements_end());
     DIExpr = Builder.createExpression(Ops);
   }
@@ -1398,8 +1356,9 @@ void llvm::salvageDebugInfo(Instruction &I) {
         auto *DIExpr = DVI->getExpression();
         DIBuilder DIB(M, /*AllowUnresolved*/ false);
         // GEP offsets are i32 and thus always fit into an int64_t.
-        DIExpr = prependDIExpr(DIB, DIExpr, NoDeref, Offset.getSExtValue(),
-                               WithStackValue);
+        DIExpr = DIExpression::prependDIExpr(DIB, DIExpr, NoDeref,
+                                             Offset.getSExtValue(),
+                                             WithStackValue);
         DVI->setOperand(0, MDWrap(I.getOperand(0)));
         DVI->setOperand(3, MetadataAsValue::get(I.getContext(), DIExpr));
         DEBUG(dbgs() << "SALVAGE: " << *DVI << '\n');
@@ -1411,7 +1370,7 @@ void llvm::salvageDebugInfo(Instruction &I) {
       // Rewrite the load into DW_OP_deref.
       auto *DIExpr = DVI->getExpression();
       DIBuilder DIB(M, /*AllowUnresolved*/ false);
-      DIExpr = prependDIExpr(DIB, DIExpr, WithDeref);
+      DIExpr = DIExpression::prependDIExpr(DIB, DIExpr, WithDeref);
       DVI->setOperand(0, MDWrap(I.getOperand(0)));
       DVI->setOperand(3, MetadataAsValue::get(I.getContext(), DIExpr));
       DEBUG(dbgs() << "SALVAGE:  " << *DVI << '\n');