Commit 87ddf1f4 authored by Johannes Doerfert's avatar Johannes Doerfert
Browse files

[Attributor] Simple casts preserve no-alias property 

This is a minimal but important advancement over the existing code. A
cast with an operand that is only used in the cast retains the no-alias
property of the operand.
parent 1c0ebcca

llvm/lib/Transforms/IPO/Attributor.cpp

+18 −2
Original line number Diff line number Diff line
@@ -2496,13 +2496,29 @@ struct AANoAliasFloating final : AANoAliasImpl { 
  /// See AbstractAttribute::initialize(...).

  void initialize(Attributor &A) override {

    AANoAliasImpl::initialize(A);

    Value &Val = getAssociatedValue();

    Value *Val = &getAssociatedValue();

    do {

      CastInst *CI = dyn_cast<CastInst>(Val);

      if (!CI)

        break;

      Value *Base = CI->getOperand(0);

      if (Base->getNumUses() != 1)

        break;

      Val = Base;

    } while (true);



    if (isa<AllocaInst>(Val))

      indicateOptimisticFixpoint();

    else if (isa<ConstantPointerNull>(Val) &&

             !NullPointerIsDefined(getAnchorScope(),

                                   Val.getType()->getPointerAddressSpace()))

                                   Val->getType()->getPointerAddressSpace()))

      indicateOptimisticFixpoint();

    else if (Val != &getAssociatedValue()) {

      const auto &ValNoAliasAA =

          A.getAAFor<AANoAlias>(*this, IRPosition::value(*Val));

      if (ValNoAliasAA.isKnownNoAlias())

        indicateOptimisticFixpoint();

    }

  }



  /// See AbstractAttribute::updateImpl(...).

llvm/test/Transforms/Attributor/noalias.ll

+35 −0
Original line number Diff line number Diff line
@@ -40,6 +40,13 @@ define i8* @return_noalias_looks_like_capture(){ 
  ret i8* %1

}



; CHECK: define noalias i16* @return_noalias_casted()

define i16* @return_noalias_casted(){

  %1 = tail call noalias i8* @malloc(i64 4)

  %c = bitcast i8* %1 to i16*

  ret i16* %c

}



declare i8* @alias()



; TEST 3
@@ -294,3 +301,31 @@ define void @test12_4(){ 
  tail call void @two_args(i8* %A_0, i8* %B_0)

  ret void

}



; TEST 13

define void @use_i8_internal(i8* %a) {

  call void @use_i8(i8* %a)

  ret void

}



define void @test13_use_noalias(){

  %m1 = tail call noalias i8* @malloc(i64 4)

  %c1 = bitcast i8* %m1 to i16*

  %c2 = bitcast i16* %c1 to i8*

; CHECK: call void @use_i8_internal(i8* noalias nocapture %c2)

  call void @use_i8_internal(i8* %c2)

  ret void

}



define void @test13_use_alias(){

  %m1 = tail call noalias i8* @malloc(i64 4)

  %c1 = bitcast i8* %m1 to i16*

  %c2a = bitcast i16* %c1 to i8*

  %c2b = bitcast i16* %c1 to i8*

; CHECK: call void @use_i8_internal(i8* nocapture %c2a)

; CHECK: call void @use_i8_internal(i8* nocapture %c2b)

  call void @use_i8_internal(i8* %c2a)

  call void @use_i8_internal(i8* %c2b)

  ret void

}