[PATCH] StructurizeCFG: Fix inverting a branch on an argument

[Tom Stellard]

On Sat, Nov 16, 2013 at 09:48:53PM -0800, Matt Arsenault wrote:
> http://llvm-reviews.chandlerc.com/D2196
> 
> Files:
>   lib/Transforms/Scalar/StructurizeCFG.cpp
>   test/Transforms/StructurizeCFG/branch-on-argument.ll
> 
> Index: lib/Transforms/Scalar/StructurizeCFG.cpp
> ===================================================================
> --- lib/Transforms/Scalar/StructurizeCFG.cpp
> +++ lib/Transforms/Scalar/StructurizeCFG.cpp
> @@ -323,21 +323,32 @@
>    if (match(Condition, m_Not(m_Value(Condition))))
>      return Condition;
>  
> -  // Third: Check all the users for an invert
> -  BasicBlock *Parent = cast<Instruction>(Condition)->getParent();
> -  for (Value::use_iterator I = Condition->use_begin(),
> -       E = Condition->use_end(); I != E; ++I) {
> +  if (Instruction *Inst = dyn_cast<Instruction>(Condition)) {
> +    // Third: Check all the users for an invert
> +    BasicBlock *Parent = Inst->getParent();
> +    for (Value::use_iterator I = Condition->use_begin(),
> +           E = Condition->use_end(); I != E; ++I) {
> +
> +      Instruction *User = dyn_cast<Instruction>(*I);
> +      if (!User || User->getParent() != Parent)
> +        continue;
>  
> -    Instruction *User = dyn_cast<Instruction>(*I);
> -    if (!User || User->getParent() != Parent)
> -      continue;
> +      if (match(*I, m_Not(m_Specific(Condition))))
> +        return *I;
> +    }
> +
> +    // Last option: Create a new instruction
> +    return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
> +  }
>  
> -    if (match(*I, m_Not(m_Specific(Condition))))
> -      return *I;
> +  if (Argument *Arg = dyn_cast<Argument>(Condition)) {
> +    BasicBlock &EntryBlock = Arg->getParent()->getEntryBlock();
> +    return BinaryOperator::CreateNot(Condition,
> +                                     Arg->getName() + ".inv",
> +                                     EntryBlock.getTerminator());
>    }
>  
> -  // Last option: Create a new instruction
> -  return BinaryOperator::CreateNot(Condition, "", Parent->getTerminator());
> +  llvm_unreachable("Unhandled condition to invert");
>  }
>  
>  /// \brief Build the condition for one edge
> Index: test/Transforms/StructurizeCFG/branch-on-argument.ll
> ===================================================================
> --- /dev/null
> +++ test/Transforms/StructurizeCFG/branch-on-argument.ll
> @@ -0,0 +1,18 @@
> +; RUN: opt -S -o - -structurizecfg < %s | FileCheck %s
> +
> +; CHECK-LABEL: @invert_branch_on_arg(
> +; CHECK: entry:
> +; CHECK: %cmp.inv = xor i1 %cmp, true
> +; CHECK: phi i1 [ false, %Flow1 ], [ %cmp.inv, %entry ]
> +
> +define void @invert_branch_on_arg(i32 addrspace(1)* %out, i1 %cmp) {
> +entry:
> +  br i1 %cmp, label %for.end, label %for.body
> +
> +for.body:                                         ; preds = %entry, %for.body
> +  store i32 999, i32 addrspace(1)* %out, align 4
> +  br label %for.body
> +
> +for.end:                                          ; preds = %Flow
> +  ret void
> +}

Is it possible to write a testcase for this that doesn't include an
infinite loop?

-Tom