[llvm-bugs] [Bug 35616] New: -callsite-splitting gives different result if dbg.value is present

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=35616

            Bug ID: 35616
           Summary: -callsite-splitting gives different result if
                    dbg.value is present
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: mikael.holmen at ericsson.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 19533
  --> https://bugs.llvm.org/attachment.cgi?id=19533&action=edit
reproducer

Doing
 opt -S -o - foo2.ll -callsite-splitting
and
 opt -S -o - foo2.ll -strip-debug -callsite-splitting

on

define internal i16 @bar(i16 %p1, i16 %p2) {
  %_tmp3 = mul i16 %p2, %p1
  ret i16 %_tmp3
}

define i16 @foo(i16 %in) {
  br label %bb1

bb1:
  %_tmp0 = icmp ne i16 %in, 0
  br i1 %_tmp0, label %bb2, label %bb3

bb2:
  br label %bb3

bb3:
  %_tmp1 = phi i16 [ 0, %bb1 ], [ 1, %bb2 ]
  %c = phi i16 [ 2, %bb1 ], [ 3, %bb2 ]
  call void @llvm.dbg.value(metadata i16 %c, metadata !7, metadata
!DIExpression()), !dbg !8
  %_tmp2 = call i16 @bar(i16 %_tmp1, i16 5)
  ret i16 %_tmp2
}

; Function Attrs: nounwind readnone speculatable
declare void @llvm.dbg.value(metadata, metadata, metadata) #0

attributes #0 = { nounwind readnone speculatable }

!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!2, !3}
!llvm.ident = !{!4}

!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "My
Compiler")
!1 = !DIFile(filename: "foo.c", directory: "/bar")

!2 = !{i32 2, !"Dwarf Version", i32 4}
!3 = !{i32 2, !"Debug Info Version", i32 3}
!4 = !{!"My Compiler"}

!5 = !DIBasicType(name: "int", size: 16, encoding: DW_ATE_signed)

!6 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 4, unit:
!0)
!7 = !DILocalVariable(name: "c", scope: !6, line: 5, type: !5)
!8 = !DILocation(line: 5, column: 7, scope: !6)

gives different results. With the llvm.dbg.value present the optimization
doesn't trigger, but if we remove it it does.

CallSiteSplitting.cpp does a couple of calls to getFirstNonPHI(). I suppose
using getFirstNonPHIOrDbg() could help ignoring the llvm.dbg.value but I have
no idea if more changes are needed.

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