[llvm-bugs] [Bug 36104] New: LoopUnrollPass is not updating parameters of DbgValueInst correctly

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36104

            Bug ID: 36104
           Summary: LoopUnrollPass is not updating parameters of
                    DbgValueInst correctly
           Product: libraries
           Version: 5.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: agupta at tifr.res.in
                CC: llvm-bugs at lists.llvm.org

Consider following input to LoopUnroll pass to be unrolled two times.

define i32 @main() #0 !dbg !7 {
  call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !11, metadata !12),
!dbg !13
  br label %1, !dbg !14

; <label>:1:                                      ; preds = %1, %0
  %.0 = phi i32 [ 0, %0 ], [ %3, %1 ]
  call void @llvm.dbg.value(metadata i32 %.0, i64 0, metadata !11, metadata
!12), !dbg !13
  %2 = icmp slt i32 %.0, 5, !dbg !15
  %3 = add nsw i32 %.0, 1, !dbg !18
  call void @llvm.dbg.value(metadata i32 %3, i64 0, metadata !11, metadata
!12), !dbg !13
  br i1 %2, label %1, label %4, !dbg !20, !llvm.loop !21

; <label>:4:                                      ; preds = %1
  ret i32 0, !dbg !23
}


After rotating and unrolling (unrolling requires rotating), we obtain:

define i32 @main() #0 !dbg !7 {
  call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !11, metadata !12),
!dbg !13
  br label %1, !dbg !14

; <label>:1:                                      ; preds = %6, %0
  %.0 = phi i32 [ 0, %0 ], [ %8, %6 ]
  call void @llvm.dbg.value(metadata i32 %.0, i64 0, metadata !11, metadata
!12), !dbg !13
  %2 = add nuw nsw i32 %.0, 1, !dbg !15
  call void @llvm.dbg.value(metadata i32 %2, i64 0, metadata !11, metadata
!12), !dbg !13
  call void @llvm.dbg.value(metadata i32 %.0, i64 0, metadata !11, metadata
!12), !dbg !13
  %3 = icmp ult i32 %2, 5, !dbg !19
  %4 = add nuw nsw i32 %2, 1, !dbg !15
  call void @llvm.dbg.value(metadata i32 %2, i64 0, metadata !11, metadata
!12), !dbg !13
  br i1 %3, label %6, label %5, !dbg !20, !llvm.loop !21

; <label>:5:                                      ; preds = %1
  ret i32 0, !dbg !23

; <label>:6:                                      ; preds = %1
  call void @llvm.dbg.value(metadata i32 %.0, i64 0, metadata !11, metadata
!12), !dbg !13
  %7 = add nuw nsw i32 %4, 1, !dbg !15
  call void @llvm.dbg.value(metadata i32 %2, i64 0, metadata !11, metadata
!12), !dbg !13
  call void @llvm.dbg.value(metadata i32 %.0, i64 0, metadata !11, metadata
!12), !dbg !13
  %8 = add nuw nsw i32 %7, 1, !dbg !15
  call void @llvm.dbg.value(metadata i32 %2, i64 0, metadata !11, metadata
!12), !dbg !13
  br label %1
}



Look at the the copied body in block 6. Note that the dbg.value after %7 is not
updated and still reflects %2. IMHO, it is wrong cloning of the block.


I think the problem lies in the following function of LoopUnroll.cpp:67

static inline void remapInstruction(Instruction *I,
                                    ValueToValueMapTy &VMap) {
  for (unsigned op = 0, E = I->getNumOperands(); op != E; ++op) {
    Value *Op = I->getOperand(op); <<<<<<<------------------------
    ValueToValueMapTy::iterator It = VMap.find(Op);
    if (It != VMap.end())
      I->setOperand(op, It->second); <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
  }

  if (PHINode *PN = dyn_cast<PHINode>(I)) {
    for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
      ValueToValueMapTy::iterator It = VMap.find(PN->getIncomingBlock(i));
      if (It != VMap.end())
        PN->setIncomingBlock(i, cast<BasicBlock>(It->second));
    }
  }
}


This function fails to pick the the right argument of a DbgValueInst. 0th Op is
not a Value but a metadata that contains the value %2 and needs one more
redirection to update the reference to %2.

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