[GVN] Use after free during load PRE

[nikic]

; RUN: opt -S -passes=gvn < %s
define i64 @test(i1 %c, ptr %p) {
entry:
  br label %loop

loop:
  %iv = phi i64 [ 0, %entry ], [ %add, %loop.latch ]
  %ptr.iv = phi ptr [ %p, %entry ], [ %select, %loop.latch ]
  %icmp = icmp eq i64 %iv, 0
  br i1 %icmp, label %exit, label %loop.cont

loop.cont:
  %add = add i64 %iv, -1
  br i1 %c, label %exit, label %loop.latch

loop.latch:
  %load = load i64, ptr %ptr.iv, align 8
  %load6 = load i64, ptr null, align 8
  %icmp7 = icmp ugt i64 %load, %load6
  %select = select i1 %icmp7, ptr %ptr.iv, ptr null
  br label %loop

exit:
  %res = load i64, ptr %ptr.iv, align 8
  ret i64 %res
}

Produces a use after free.

[nikic]

I believe the problem is that replaceValuesPerBlockEntry() doesn't handle select values.

[nikic]

/cherry-pick 7f1733a

[llvmbot]

/branch llvm/llvm-project-release-prs/issue69301