[llvm] r312318 - Debug info for variables whose type is shrinked to bool

[Richard Trieu via llvm-commits]

+Nikola

On Fri, Sep 1, 2017 at 3:05 AM, Strahinja Petrovic via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: spetrovic
> Date: Fri Sep  1 03:05:27 2017
> New Revision: 312318
>
> URL: http://llvm.org/viewvc/llvm-project?rev=312318&view=rev
> Log:
> Debug info for variables whose type is shrinked to bool
>
> This patch provides such debug information for integer
> variables whose type is shrinked to bool by providing
> dwarf expression which returns either constant initial
> value or other value.
>
> Patch by Nikola Prica.
>
> Differential Revision: https://reviews.llvm.org/D35994
>
> Modified:
>     llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
>     llvm/trunk/lib/IR/DebugInfoMetadata.cpp
>     llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/A
> smPrinter/DwarfExpression.cpp?rev=312318&r1=312317&r2=312318&view=diff
> ============================================================
> ==================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.cpp (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.cpp Fri Sep  1
> 03:05:27 2017
> @@ -338,6 +338,7 @@ void DwarfExpression::addExpression(DIEx
>        break;
>      case dwarf::DW_OP_plus:
>      case dwarf::DW_OP_minus:
> +    case dwarf::DW_OP_mul:
>        emitOp(Op->getOp());
>        break;
>      case dwarf::DW_OP_deref:
>
> Modified: llvm/trunk/lib/IR/DebugInfoMetadata.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/DebugI
> nfoMetadata.cpp?rev=312318&r1=312317&r2=312318&view=diff
> ============================================================
> ==================
> --- llvm/trunk/lib/IR/DebugInfoMetadata.cpp (original)
> +++ llvm/trunk/lib/IR/DebugInfoMetadata.cpp Fri Sep  1 03:05:27 2017
> @@ -643,6 +643,7 @@ bool DIExpression::isValid() const {
>      case dwarf::DW_OP_plus_uconst:
>      case dwarf::DW_OP_plus:
>      case dwarf::DW_OP_minus:
> +    case dwarf::DW_OP_mul:
>      case dwarf::DW_OP_deref:
>      case dwarf::DW_OP_xderef:
>        break;
>
> Modified: llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transform
> s/IPO/GlobalOpt.cpp?rev=312318&r1=312317&r2=312318&view=diff
> ============================================================
> ==================
> --- llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp (original)
> +++ llvm/trunk/lib/Transforms/IPO/GlobalOpt.cpp Fri Sep  1 03:05:27 2017
> @@ -36,6 +36,7 @@
>  #include "llvm/IR/Module.h"
>  #include "llvm/IR/Operator.h"
>  #include "llvm/IR/ValueHandle.h"
> +#include "llvm/IR/DebugInfoMetadata.h"
>  #include "llvm/Pass.h"
>  #include "llvm/Support/Debug.h"
>  #include "llvm/Support/ErrorHandling.h"
> @@ -1603,12 +1604,47 @@ static bool TryToShrinkGlobalToBoolean(G
>    assert(InitVal->getType() != Type::getInt1Ty(GV->getContext()) &&
>           "No reason to shrink to bool!");
>
> +  SmallVector<DIGlobalVariableExpression *, 1> GVs;
> +  GV->getDebugInfo(GVs);
> +
>    // If initialized to zero and storing one into the global, we can use a
> cast
>    // instead of a select to synthesize the desired value.
>    bool IsOneZero = false;
> -  if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal))
> +  if (ConstantInt *CI = dyn_cast<ConstantInt>(OtherVal)){
>      IsOneZero = InitVal->isNullValue() && CI->isOne();
>
> +    ConstantInt *CIInit = dyn_cast<ConstantInt>(GV->getInitializer());
> +    uint64_t ValInit = CIInit->getZExtValue();
>

I am seeing a crash from a null dereference at this point.  dyn_cast can
return in a null pointer and is usually a sign of trouble if it is not
check for non-nullness before use.  In this case, CIInit can possibly be
null.  I am reducing a test case at the moment, and will update with more
details.


> +    uint64_t ValOther = CI->getZExtValue();
> +    uint64_t ValMinus = ValOther - ValInit;
> +
> +    for(auto *GVe : GVs){
> +      DIGlobalVariable *DGV = GVe->getVariable();
> +      DIExpression *E = GVe->getExpression();
> +
> +      // val * (ValOther - ValInit) + ValInit:
> +      // DW_OP_deref DW_OP_constu <ValMinus>
> +      // DW_OP_mul DW_OP_constu <ValInit> DW_OP_plus DW_OP_stack_value
> +      E = DIExpression::get(NewGV->getContext(),
> +                           {dwarf::DW_OP_deref,
> +                            dwarf::DW_OP_constu,
> +                            ValMinus,
> +                            dwarf::DW_OP_mul,
> +                            dwarf::DW_OP_constu,
> +                            ValInit,
> +                            dwarf::DW_OP_plus,
> +                            dwarf::DW_OP_stack_value});
> +      DIGlobalVariableExpression *DGVE =
> +        DIGlobalVariableExpression::get(NewGV->getContext(), DGV, E);
> +      NewGV->addDebugInfo(DGVE);
> +    }
> +  } else {
> +    // FIXME: This will only emit address for debugger on which will
> +    // be written only 0 or 1.
> +    for(auto *GV : GVs)
> +      NewGV->addDebugInfo(GV);
> +  }
> +
>    while (!GV->use_empty()) {
>      Instruction *UI = cast<Instruction>(GV->user_back());
>      if (StoreInst *SI = dyn_cast<StoreInst>(UI)) {
>
>
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