[llvm-bugs] [Bug 45444] New: Invalid transform: gep p, (q-p) -> q

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=45444

            Bug ID: 45444
           Summary: Invalid transform: gep p, (q-p) -> q
           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: efriedma at quicinc.com, juneyoung.lee at sf.snu.ac.kr,
                    lebedev.ri at gmail.com, llvm-bugs at lists.llvm.org,
                    regehr at cs.utah.edu, spatel+llvm at rotateright.com

Unit test: Transforms/InstCombine/getelementptr.ll
Summary: just because 2 pointers have the same integer value it doesn't mean
they are the same pointer. While %gep is in bounds, %c2 may refer to another
object with an OOB pointer.

define * @test45(* %c1, * %c2) {
%0:
  %ptrtoint1 = ptrtoint * %c1 to i64
  %ptrtoint2 = ptrtoint * %c2 to i64
  %sub = sub i64 %ptrtoint2, %ptrtoint1
  %shr = sdiv i64 %sub, 7
  %gep = gep inbounds * %c1, 7 x i64 %shr
  ret * %gep
}
=>
define * @test45(* %c1, * %c2) {
%0:
  %gep = bitcast * %c2 to *
  ret * %gep
}
Transformation doesn't verify!
ERROR: Value mismatch

Example:
* %c1 = pointer(non-local, block_id=1, offset=7790792235569643584)
* %c2 = pointer(non-local, block_id=0, offset=8251192938491543615)

Source:
i64 %ptrtoint1 = #x72907442c8000040 (8255225947142225984)
i64 %ptrtoint2 = #x72822042c800003f (8251192938491543615)
i64 %sub = #xfff1abffffffffff (18442711065058869247, -4033008650682369)
i64 %shr = #xfffdf40000000000 (18446167929616596992, -576144092954624)
* %gep = pointer(non-local, block_id=1, offset=7786759226918961216)

Target:
* %gep = pointer(non-local, block_id=0, offset=8251192938491543615)
Source value: pointer(non-local, block_id=1, offset=7786759226918961216)
Target value: pointer(non-local, block_id=0, offset=8251192938491543615)


https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=2009353267698970&test=Transforms%2FInstCombine%2Fgetelementptr.ll

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