[PATCH] D65593: [Attributor][MustExec] Deduce dereferenceable and nonnull attribute by exploring path

[Hideto Ueno via Phabricator via llvm-commits]

uenoku created this revision.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a reviewer: jdoerfert.
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In this patch, `MustBeExecutedContextExplorer` is extended to traverse the path and nonnull and dereferenceable are deduced more. This patch introduces a prototype for traversing path and geting information.
For example,

  I_1
  I_2
  if(...){
      T_1
  }else{
      F_1
  }
  E_1
  E_2
  ...

If we assume that I_1 is executed and all instructions are `willreturn` and `nounwind`, we can get following formula(P is a function that takes Instruction and returns some State(Formula)).

P(I_1) \/P(l_2) \/ (P(T_1) /\ P(F_1)) \/ P(E_1) \/ P(E_2)

This enables us this deduction:

  define void @f7(i8* %a, i8 %c) { 
    %cmp = icmp eq i8 %c, 0
    tail call void @fun1(i8* dereferenceable(4) %a)
    br i1 %cmp, label %cont.then, label %cont.else
  cont.then:
    tail call void @fun1(i8* dereferenceable(12) %a)
    br label %cont2
  cont.else:
    tail call void @fun1(i8* dereferenceable(16) %a)
    br label %cont2
  cont2:
    tail call void @fun1(i8* dereferenceable(8) %a)
    ret void
  }
  ; -> %a is dereferenceable(12)

Currently, the state(`ASBool, ASDeref`) is implemented new for an experiment but, needless to say, the state is very similar to `Attributor::AbstractState` so I think it is better to reuse `AbstractState`.


https://reviews.llvm.org/D65593

Files:
  llvm/include/llvm/Analysis/MustExecute.h
  llvm/lib/Analysis/MustExecute.cpp
  llvm/lib/Transforms/IPO/Attributor.cpp
  llvm/test/Transforms/FunctionAttrs/dereferenceable.ll
  llvm/test/Transforms/FunctionAttrs/nonnull.ll

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