[llvm-bugs] [Bug 42619] New: DivRemPairs is incorrect in the presence of undef

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42619

            Bug ID: 42619
           Summary: DivRemPairs is incorrect in the presence of undef
           Product: libraries
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: nunoplopes at sapo.pt
                CC: llvm-bugs at lists.llvm.org, regehr at cs.utah.edu,
                    spatel+llvm at rotateright.com

See, for example:

$ opt -div-rem-pairs Transforms/DivRemPairs/X86/div-rem-pairs.ll

define void @decompose_illegal_srem_same_block(i32 %a, i32 %b) {
  %rem = srem i32 %a, %b
  %div = sdiv i32 %a, %b
  call void @foo(i32 %rem, i32 %div)
  ret void
}
=>
define void @decompose_illegal_srem_same_block(i32 %a, i32 %b) {
  %div = sdiv i32 %a, %b
  %1 = mul i32 %div, %b
  %2 = sub i32 %a, %1
  call void @foo(i32 %2, i32 %div)
  ret void
}
Transformation doesn't verify!
ERROR: Source is more defined than target

Example:
i32 %a = undef
i32 %b = #x00000001 (1)

Source:
i32 %rem = #x00000000 (0)
i32 %div = undef

Target:
i32 %div = #x7fffffff (2147483647)
i32 %1 = undef
i32 %2 = undef

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