Commit 6770fbb3 authored by Akira Hatanaka's avatar Akira Hatanaka
Browse files

[ObjC][ARC] Delete ARC runtime calls that take inert phi values 

This improves on the following patch, which removed ARC runtime calls
taking inert global variables:

https://reviews.llvm.org/D62433

rdar://problem/59137105
parent ba9cae58

llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp

+32 −12
Original line number Diff line number Diff line
@@ -877,23 +877,43 @@ void ObjCARCOpt::OptimizeIndividualCalls(Function &F) { 
  optimizeDelayedAutoreleaseRV();

}



/// This function returns true if the value is inert. An ObjC ARC runtime call

/// taking an inert operand can be safely deleted.

static bool isInertARCValue(Value *V) {

  V = V->stripPointerCasts();



  if (IsNullOrUndef(V))

    return true;



  // See if this is a global attribute annotated with an 'objc_arc_inert'.

  if (auto *GV = dyn_cast<GlobalVariable>(V))

    if (GV->hasAttribute("objc_arc_inert"))

      return true;



  if (auto PN = dyn_cast<PHINode>(V)) {

    // Look through phis's operands.

    for (Value *Opnd : PN->incoming_values())

      if (!isInertARCValue(Opnd))

        return false;

    return true;

  }



  return false;

}



void ObjCARCOpt::OptimizeIndividualCallImpl(

    Function &F, DenseMap<BasicBlock *, ColorVector> &BlockColors,

    Instruction *Inst, ARCInstKind Class, const Value *Arg) {

  LLVM_DEBUG(dbgs() << "Visiting: Class: " << Class << "; " << *Inst << "\n");



  // Some of the ARC calls can be deleted if their arguments are global

  // variables that are inert in ARC.

  if (IsNoopOnGlobal(Class)) {

    Value *Opnd = Inst->getOperand(0);

    if (auto *GV = dyn_cast<GlobalVariable>(Opnd->stripPointerCasts()))

      if (GV->hasAttribute("objc_arc_inert")) {

  // We can delete this call if it takes an inert value.

  if (IsNoopOnGlobal(Class))

    if (isInertARCValue(Inst->getOperand(0))) {

      if (!Inst->getType()->isVoidTy())

          Inst->replaceAllUsesWith(Opnd);

        Inst->replaceAllUsesWith(Inst->getOperand(0));

      Inst->eraseFromParent();

      return;

    }

  }



  switch (Class) {

  default:

llvm/test/Transforms/ObjCARC/inert-global.ll

+33 −0
Original line number Diff line number Diff line
@@ -54,6 +54,39 @@ define internal void @__globalBlock_block_invoke(i8* nocapture readnone) { 
  ret void

}



; CHECK: define %[[V0:.*]]* @test_conditional0(

; CHECK: %[[PHI0:.*]] = phi %[[V0]]* [ bitcast (%struct.__NSConstantString_tag* @_unnamed_cfstring_ to %[[V0]]*), %{{.*}} ], [ null, %{{.*}} ]



; CHECK: %[[PHI1:.*]] = phi %[[V0]]* [ bitcast (%struct.__NSConstantString_tag* @_unnamed_cfstring_ to %[[V0]]*), %{{.*}} ], [ %[[PHI0]], %{{.*}} ]

; CHECK-NEXT: %[[PHI2:.*]] = phi %[[V0]]* [ bitcast (%struct.__NSConstantString_tag* @_unnamed_cfstring_ to %[[V0]]*), %{{.*}} ], [ %{{.*}}, %{{.*}} ]

; CHECK-NEXT: %[[V2:.*]] = bitcast %[[V0]]* %[[PHI1]] to i8*

; CHECK-NEXT: %[[V4:.*]] = bitcast %[[V0]]* %[[PHI2]] to i8*

; CHECK-NEXT: %[[V5:.*]] = tail call i8* @llvm.objc.autoreleaseReturnValue(i8* %[[V4]])

; CHECK-NEXT: ret %[[V0]]* %[[PHI2]]



define %0* @test_conditional0(i32 %i, %0* %b) {

entry:

  %v0 = icmp eq i32 %i, 1

  br i1 %v0, label %bb2, label %bb1



bb1:

  %v1 = icmp eq i32 %i, 2

  br i1 %v1, label %bb2, label %return



bb2:

  %phi0 = phi %0* [ bitcast (%struct.__NSConstantString_tag* @_unnamed_cfstring_ to %0*), %entry ], [ null, %bb1 ]

  br label %return



return:

  %phi1 = phi %0* [ bitcast (%struct.__NSConstantString_tag* @_unnamed_cfstring_ to %0*), %bb1 ], [ %phi0, %bb2 ]

  %phi2 = phi %0* [ bitcast (%struct.__NSConstantString_tag* @_unnamed_cfstring_ to %0*), %bb1 ], [ %b, %bb2 ]

  %v2 = bitcast %0* %phi1 to i8*

  %v3 = tail call i8* @llvm.objc.autoreleaseReturnValue(i8* %v2)

  %v4 = bitcast %0* %phi2 to i8*

  %v5 = tail call i8* @llvm.objc.autoreleaseReturnValue(i8* %v4)

  ret %0* %phi2

}



declare void @foo()



declare i8* @llvm.objc.retain(i8*) local_unnamed_addr