[llvm-bugs] [Bug 45481] New: Can't remove insertelement undef

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=45481

            Bug ID: 45481
           Summary: Can't remove insertelement undef
           Product: libraries
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Keywords: miscompilation
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: nunoplopes at sapo.pt
                CC: lebedev.ri at gmail.com, llvm-bugs at lists.llvm.org,
                    regehr at cs.utah.edu, spatel+llvm at rotateright.com

Test: Transforms/InstSimplify/insertelement.ll
Summary: We can't remove insertelement undef to a vector, since it may be
replacing a poison value.

define <4 x i32> @PR1286(<4 x i32> %A) {
  %B = insertelement <4 x i32> %A, i32 undef, i32 1
  ret <4 x i32> %B
}
=>
define <4 x i32> @PR1286(<4 x i32> %A) {
  ret <4 x i32> %A
}
Transformation doesn't verify!
ERROR: Target is more poisonous than source

Example:
<4 x i32> %A = < poison, poison, poison, poison >

Source:
<4 x i32> %B = < poison, undef, poison, poison >

Target:
Source value: < poison, undef, poison, poison >
Target value: < poison, poison, poison, poison >


Report:
https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=ed3ac07d4817b221&test=Transforms%2FInstSimplify%2Finsertelement.ll

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