Commit e5f07080 authored by Bjorn Pettersson's avatar Bjorn Pettersson
Browse files

[BasicBlockUtils] Fix dbg.value elimination problem in MergeBlockIntoPredecessor 

Summary:
In commit d60f34c2 (llvm-svn 317128,
PR35113) MergeBlockIntoPredecessor was changed into
discarding some dbg.value intrinsics referring to
PHI values, post-splice due to loop rotation.

That elimination of dbg.value intrinsics did not
consider which dbg.value to keep depending on the
context (e.g. if the variable is changing its value
several times inside the basic block).

In the past that hasn't been such a big problem since
CodeGenPrepare::placeDbgValues has moved the dbg.value
to be next to the PHI node anyway. But after commit
00e23889 CodeGenPrepare isn't doing that
any longer, so we need to be more careful when avoiding
duplicate dbg.value intrinsics in MergeBlockIntoPredecessor.

This patch replaces the code that tried to avoid duplicate
dbg.values by using the RemoveRedundantDbgInstrs helper.

Reviewers: aprantl, jmorse, vsk

Reviewed By: aprantl, vsk

Subscribers: jholewinski, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71480
parent 632deb6b

llvm/lib/Transforms/Utils/BasicBlockUtils.cpp

+4 −14
Original line number Diff line number Diff line
@@ -284,20 +284,10 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU, 
  // Add unreachable to now empty BB.

  new UnreachableInst(BB->getContext(), BB);



  // Eliminate duplicate dbg.values describing the entry PHI node post-splice.

  for (auto Incoming : IncomingValues) {

    if (isa<Instruction>(*Incoming)) {

      SmallVector<DbgValueInst *, 2> DbgValues;

      SmallDenseSet<std::pair<DILocalVariable *, DIExpression *>, 2>

          DbgValueSet;

      llvm::findDbgValues(DbgValues, Incoming);

      for (auto &DVI : DbgValues) {

        auto R = DbgValueSet.insert({DVI->getVariable(), DVI->getExpression()});

        if (!R.second)

          DVI->eraseFromParent();

      }

    }

  }

  // Eliminate duplicate/redundant dbg.values. This seems to be a good place to

  // do that since we might end up with redundant dbg.values describing the

  // entry PHI node post-splice.

  RemoveRedundantDbgInstrs(PredBB);



  // Inherit predecessors name if it exists.

  if (!PredBB->hasName())

llvm/test/DebugInfo/NVPTX/debug-loc-offset.ll

+2 −2
Original line number Diff line number Diff line
@@ -43,8 +43,8 @@ declare void @llvm.dbg.value(metadata, metadata, metadata) #1 
; CHECK: .loc [[CU2:[0-9]+]] 6 0

; CHECK: Lfunc_begin1:

; CHECK: .loc [[CU2]] 6 0

; CHECK: //DEBUG_VALUE: baz:z <- {{[0-9]+}}

; CHECK: //DEBUG_VALUE: baz:z <- {{[0-9]+}}

; CHECK-NOT: //DEBUG_VALUE: baz:z

; CHECK: //DEBUG_VALUE: baz:z <- undef

; CHECK: .loc [[CU2]] 10 0

; CHECK: ret;

; CHECK: }

llvm/test/Transforms/LoopRotate/dbg-value-duplicates-2.ll

+1 −3
Original line number Diff line number Diff line
@@ -11,12 +11,10 @@ define dso_local i16 @main() local_unnamed_addr #0 !dbg !7 { 
; CHECK-NEXT:    call void @llvm.dbg.value(metadata i16 [[TMP1]], metadata !12, metadata !DIExpression()), !dbg !13

; CHECK-NEXT:    [[TMP4:%.*]] = call i16 @wibble(i16 [[TMP1]]), !dbg !14

; CHECK-NEXT:    [[TMP5]] = add nsw i16 [[TMP4]], [[TMP1]], !dbg !14

; CHECK-NEXT:    call void @llvm.dbg.value(metadata i16 [[TMP5]], metadata !12, metadata !DIExpression()), !dbg !13

; CHECK-NEXT:    [[TMP6:%.*]] = call i16 @wibble(i16 [[TMP4]]), !dbg !14

; CHECK-NEXT:    [[TMP7:%.*]] = mul nsw i16 [[TMP6]], 3, !dbg !14

; CHECK-NEXT:    [[TMP8:%.*]] = call i16 @wibble(i16 [[TMP7]]), !dbg !14

; BUG: This dbg.value is expected to be placed directly after the add above.

;      Otherwise variable "x" (!12) won't be described as having the correct value at the call to wibble just after the add.

; CHECK-NEXT:    call void @llvm.dbg.value(metadata i16 [[TMP5]], metadata !12, metadata !DIExpression()), !dbg !13

; CHECK-NEXT:    [[TMP2:%.*]] = icmp slt i16 [[TMP5]], 17, !dbg !14

; CHECK-NEXT:    br i1 [[TMP2]], label [[BB2]], label [[BB3:%.*]], !dbg !14

; CHECK:       bb3:

llvm/test/Transforms/SimplifyCFG/hoist-dbgvalue-inlined.ll

+0 −1
Original line number Diff line number Diff line
@@ -8,7 +8,6 @@ init: 


; CHECK:  %vala = load i64, i64* %ptr

; CHECK-NEXT:  call void @llvm.dbg.value(metadata i64 %vala, metadata [[MD:![0-9]*]]

; CHECK-NEXT:  call void @llvm.dbg.value(metadata i64 %vala, metadata [[MD]]

; CHECK-NEXT:  %valbmasked = and i64 %vala, 1



a:                                              ; preds = %init