Commit 829d377a authored by Nikita Popov's avatar Nikita Popov
Browse files

[InstSimplify] Don't simplify musttail calls 

As pointed out by jdoerfert on D75815, we must be careful when
simplifying musttail calls: We can only replace the return value
if we can eliminate the call entirely. As we can't make this
guarantee for all consumers of InstSimplify, this patch disables
simplification of musttail calls. Without this patch, musttail
simplification currently results in module verification errors.

Differential Revision: https://reviews.llvm.org/D75824
parent 843a9778

llvm/lib/Analysis/InstructionSimplify.cpp

+8 −0
Original line number Diff line number Diff line
@@ -5330,6 +5330,11 @@ static Value *simplifyIntrinsic(CallBase *Call, const SimplifyQuery &Q) { 
Value *llvm::SimplifyCall(CallBase *Call, const SimplifyQuery &Q) {

  Value *Callee = Call->getCalledValue();



  // musttail calls can only be simplified if they are also DCEd.

  // As we can't guarantee this here, don't simplify them.

  if (Call->isMustTailCall())

    return nullptr;



  // call undef -> undef

  // call null -> undef

  if (isa<UndefValue>(Callee) || isa<ConstantPointerNull>(Callee))
@@ -5512,6 +5517,9 @@ Value *llvm::SimplifyInstruction(Instruction *I, const SimplifyQuery &SQ, 
    break;

  case Instruction::Call: {

    Result = SimplifyCall(cast<CallInst>(I), Q);

    // Don't perform known bits simplification below for musttail calls.

    if (cast<CallInst>(I)->isMustTailCall())

      return Result;

    break;

  }

  case Instruction::Freeze:

llvm/test/Transforms/InstSimplify/call.ll

+27 −0
Original line number Diff line number Diff line
@@ -1007,3 +1007,30 @@ define i32 @returned_var_arg(i32 %arg) { 
  %x = call i32 @passthru_i32(i32 %arg)

  ret i32 %x

}



define i32 @returned_const_int_arg_musttail(i32 %arg) {

; CHECK-LABEL: @returned_const_int_arg_musttail(

; CHECK-NEXT:    [[X:%.*]] = musttail call i32 @passthru_i32(i32 42)

; CHECK-NEXT:    ret i32 [[X]]

;

  %x = musttail call i32 @passthru_i32(i32 42)

  ret i32 %x

}



define i32 @returned_var_arg_musttail(i32 %arg) {

; CHECK-LABEL: @returned_var_arg_musttail(

; CHECK-NEXT:    [[X:%.*]] = musttail call i32 @passthru_i32(i32 [[ARG:%.*]])

; CHECK-NEXT:    ret i32 [[X]]

;

  %x = musttail call i32 @passthru_i32(i32 %arg)

  ret i32 %x

}



define i32 @call_undef_musttail() {

; CHECK-LABEL: @call_undef_musttail(

; CHECK-NEXT:    [[X:%.*]] = musttail call i32 undef()

; CHECK-NEXT:    ret i32 [[X]]

;

  %x = musttail call i32 undef()

  ret i32 %x

}