Align definition of DW_OP_plus with DWARF spec [2/3]

[sdesmalen]

Summary

This patch is part of 3 patches that together form a single patch, but must be introduced in stages in order not to break things.
 
The way that LLVM interprets DW_OP_plus in DIExpression nodes is basically that of the DW_OP_plus_uconst operator since LLVM expects an unsigned constant operand. This unnecessarily restricts the DW_OP_plus operator, preventing it from being used to describe the evaluation of runtime values on the expression stack. These patches try to align the semantics of DW_OP_plus and DW_OP_minus with that of the DWARF definition, which pops two elements off the expression stack, performs the operation and pushes the result back on the stack.
 
This is done in three stages:
• The first patch (LLVM) adds support for DW_OP_plus_uconst and changes all uses (and tests) of DW_OP_plus to use DW_OP_plus_uconst.
 
• The second patch (Clang) contains changes to use DW_OP_plus_uconst instead of DW_OP_plus.
 
• The third patch (LLVM) changes the semantics of DW_OP_plus to be in line with it’s DWARF meaning. It also does this for DW_OP_minus.

Patch by Sander de Smalen.

[aprantl]

Thanks, this LGTM!

lib/CodeGen/CGDebugInfo.cpp

void CGDebugInfo::EmitDeclare(const VarDecl *VD, llvm::Value *Storage,
   // referencing an alloca. Newer versions of LLVM don't treat allocas
   // differently from other function arguments when used in a dbg.declare.
   auto *Scope = cast<llvm::DIScope>(LexicalBlockStack.back());
   StringRef Name = VD->getName();
   if (!Name.empty()) {
     if (VD->hasAttr<BlocksAttr>()) {
       // Here, we need an offset *into* the alloca.
       CharUnits offset = CharUnits::fromQuantity(32);
-      Expr.push_back(llvm::dwarf::DW_OP_plus);
+      Expr.push_back(llvm::dwarf::DW_OP_plus_uconst);
       // offset of __forwarding field
       offset = CGM.getContext().toCharUnitsFromBits(
           CGM.getTarget().getPointerWidth(0));
       Expr.push_back(offset.getQuantity());
       Expr.push_back(llvm::dwarf::DW_OP_deref);
-      Expr.push_back(llvm::dwarf::DW_OP_plus);
+      Expr.push_back(llvm::dwarf::DW_OP_plus_uconst);
       // offset of x field
       offset = CGM.getContext().toCharUnitsFromBits(XOffset);
       Expr.push_back(offset.getQuantity());
     }
   } else if (const auto *RT = dyn_cast<RecordType>(VD->getType())) {
     // If VD is an anonymous union then Storage represents value for
     // all union fields.
     const auto *RD = cast<RecordDecl>(RT->getDecl());
void CGDebugInfo::EmitDeclareOfBlockDeclRefVariable(
   const llvm::DataLayout &target = CGM.getDataLayout();
 
   CharUnits offset = CharUnits::fromQuantity(
       target.getStructLayout(blockInfo.StructureType)
           ->getElementOffset(blockInfo.getCapture(VD).getIndex()));
 
   SmallVector<int64_t, 9> addr;
   addr.push_back(llvm::dwarf::DW_OP_deref);
-  addr.push_back(llvm::dwarf::DW_OP_plus);
+  addr.push_back(llvm::dwarf::DW_OP_plus_uconst);
   addr.push_back(offset.getQuantity());
   if (isByRef) {
     addr.push_back(llvm::dwarf::DW_OP_deref);
-    addr.push_back(llvm::dwarf::DW_OP_plus);
+    addr.push_back(llvm::dwarf::DW_OP_plus_uconst);
     // offset of __forwarding field
     offset =
         CGM.getContext().toCharUnitsFromBits(target.getPointerSizeInBits(0));
     addr.push_back(offset.getQuantity());
     addr.push_back(llvm::dwarf::DW_OP_deref);
-    addr.push_back(llvm::dwarf::DW_OP_plus);
+    addr.push_back(llvm::dwarf::DW_OP_plus_uconst);
     // offset of x field
     offset = CGM.getContext().toCharUnitsFromBits(XOffset);
     addr.push_back(offset.getQuantity());
   }
 
   // Create the descriptor for the variable.
   auto Align = getDeclAlignIfRequired(VD, CGM.getContext());
   auto *D = DBuilder.createAutoVariable(