[llvm-bugs] [Bug 25432] New: Optimization removes debug info when processing comparison to constant

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=25432

            Bug ID: 25432
           Summary: Optimization removes debug info when processing
                    comparison to constant
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: DebugInfo
          Assignee: unassignedbugs at nondot.org
          Reporter: danielcdh at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 15234
  --> https://llvm.org/bugs/attachment.cgi?id=15234&action=edit
original source file

#clang -S -O2 -g a.cc

In the produced binary:

# BB#0:
        #DEBUG_VALUE: foo:i <- EDI
        .loc    1 5 15 prologue_end     # a.cc:5:15
        cmpl    $128, %edi
        je      .LBB0_2
# BB#1:
        #DEBUG_VALUE: foo:i <- EDI
        cmpl    $80, %edi
        jne     .LBB0_3

Apparent, the cmpl in BB#1 should be attributed to ".loc 1 6 9". However its
debug info is removed by cfg-simplify.

Original IR:
define void @_Z3fooi(i32 %i) #0 {
  %1 = alloca i32, align 4
  store i32 %i, i32* %1, align 4, !tbaa !13
  call void @llvm.dbg.declare(metadata i32* %1, metadata !9, metadata !17),
!dbg !18
  %2 = load i32, i32* %1, align 4, !dbg !19, !tbaa !13
  %3 = icmp eq i32 %2, 80, !dbg !21
  br i1 %3, label %7, label %4, !dbg !22

; <label>:4                                       ; preds = %0
  %5 = load i32, i32* %1, align 4, !dbg !23, !tbaa !13
  %6 = icmp eq i32 %5, 128, !dbg !24
  br i1 %6, label %7, label %8, !dbg !25

; <label>:7                                       ; preds = %4, %0
  call void @_Z3barv(), !dbg !26
  br label %9, !dbg !26

; <label>:8                                       ; preds = %4
  call void @_Z3bazv(), !dbg !27
  br label %9

; <label>:9                                       ; preds = %8, %7
  ret void, !dbg !28
}


After some transformation (debug info still correct):
define void @_Z3fooi(i32 %i) #0 {
  call void @llvm.dbg.value(metadata i32 %i, i64 0, metadata !9, metadata !13),
!dbg !14
  %1 = icmp eq i32 %i, 80, !dbg !15
  %2 = icmp eq i32 %i, 128, !dbg !17
  %or.cond = or i1 %1, %2, !dbg !18
  br i1 %or.cond, label %3, label %4, !dbg !18

; <label>:3                                       ; preds = %0
  call void @_Z3barv(), !dbg !19
  br label %5, !dbg !19

; <label>:4                                       ; preds = %0
  call void @_Z3bazv(), !dbg !20
  br label %5

; <label>:5                                       ; preds = %4, %3
  ret void, !dbg !21
}

After cfg-simply:
define void @_Z3fooi(i32 %i) #0 {
  call void @llvm.dbg.value(metadata i32 %i, i64 0, metadata !9, metadata !13),
!dbg !14
  switch i32 %i, label %2 [
    i32 128, label %1
    i32 80, label %1
  ], !dbg !15

; <label>:1                                       ; preds = %0, %0
  call void @_Z3barv(), !dbg !17
  br label %3, !dbg !17

; <label>:2                                       ; preds = %0
  call void @_Z3bazv(), !dbg !18
  br label %3

; <label>:3                                       ; preds = %2, %1
  ret void, !dbg !19
}

The debug info is all lost here when converting compare to switch. Later when
converting to machine code, the switch is expanded to compare again, but
without correct debug info.

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