Commit b5fbbdd2 authored by Owen Anderson's avatar Owen Anderson
Browse files

Teach InstCombine to eliminate malloc-realloc-free triplets. 

Reviewed By: majnemer

Differential Revision: https://reviews.llvm.org/D109988
parent cbdf624b

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

+16 −0
Original line number Diff line number Diff line
@@ -2596,6 +2596,13 @@ static bool isAllocSiteRemovable(Instruction *AI, 
          Users.emplace_back(I);

          continue;

        }



        if (isReallocLikeFn(I, TLI, true)) {

          Users.emplace_back(I);

          Worklist.push_back(I);

          continue;

        }



        return false;



      case Instruction::Store: {
@@ -2808,6 +2815,15 @@ Instruction *InstCombinerImpl::visitFree(CallInst &FI) { 
  if (isa<ConstantPointerNull>(Op))

    return eraseInstFromFunction(FI);



  // If we had free(realloc(...)) with no intervening uses, then eliminate the

  // realloc() entirely.

  if (CallInst *CI = dyn_cast<CallInst>(Op)) {

    if (CI->hasOneUse() && isReallocLikeFn(CI, &TLI, true)) {

      return eraseInstFromFunction(

          *replaceInstUsesWith(*CI, CI->getOperand(0)));

    }

  }



  // If we optimize for code size, try to move the call to free before the null

  // test so that simplify cfg can remove the empty block and dead code

  // elimination the branch. I.e., helps to turn something like:

llvm/test/Transforms/InstCombine/alloc-realloc-free.ll

0 → 100644
+24 −0
Original line number Diff line number Diff line 
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --scrub-attributes

; RUN: opt -S -instcombine < %s | FileCheck %s



define dso_local void @test() local_unnamed_addr #0 {

; CHECK-LABEL: @test(

; CHECK-NEXT:    ret void

;

  %1 = tail call noalias align 16 dereferenceable_or_null(4) i8* @malloc(i64 4) #4

  %2 = tail call align 16 dereferenceable_or_null(6) i8* @realloc(i8* %1, i64 6) #4

  tail call void @free(i8* %2) #4

  ret void

}



declare dso_local noalias noundef i8* @malloc(i64 noundef) local_unnamed_addr #1

declare dso_local noalias noundef i8* @realloc(i8* nocapture, i64 noundef) local_unnamed_addr #2

declare dso_local void @free(i8* nocapture noundef) local_unnamed_addr #2

declare void @llvm.dbg.value(metadata, metadata, metadata) #3



attributes #0 = { mustprogress nounwind uwtable willreturn }

attributes #1 = { inaccessiblememonly mustprogress nofree nounwind willreturn }

attributes #2 = { inaccessiblemem_or_argmemonly mustprogress nounwind willreturn }

attributes #3 = { nofree nosync nounwind readnone speculatable willreturn }

attributes #4 = { nounwind }

llvm/test/Transforms/InstCombine/realloc-free.ll

0 → 100644
+19 −0
Original line number Diff line number Diff line 
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --scrub-attributes

; RUN: opt -S -instcombine < %s | FileCheck %s



define dso_local void @_Z3fooPv(i8* nocapture %0) local_unnamed_addr #0 {

; CHECK-LABEL: @_Z3fooPv(

; CHECK-NEXT:    tail call void @free(i8* [[TMP0:%.*]])

; CHECK-NEXT:    ret void

;

  %2 = tail call align 16 dereferenceable_or_null(6) i8* @realloc(i8* %0, i64 6) #2

  tail call void @free(i8* %2) #2

  ret void

}



declare dso_local noalias noundef i8* @realloc(i8* nocapture, i64 noundef) local_unnamed_addr #1

declare dso_local void @free(i8* nocapture noundef) local_unnamed_addr #1



attributes #0 = { mustprogress nounwind uwtable willreturn }

attributes #1 = { inaccessiblemem_or_argmemonly mustprogress nounwind willreturn }

attributes #2 = { nounwind }