[GVN] hits assertion "Cannot split critical edge from IndirectBrInst" in llvm::SplitKnownCriticalEdge

[tetzank]

The gvn pass cannot handle the indirectbr instruction with more than one destination. It hits an assertion in llvm::SplitKnownCriticalEdge trying to add a "dead" block after the indirectbr.
The newgvn pass works fine.

Reproducer:

define void @foo(i1 %cmp) {
first:
  br i1 %cmp, label %exit, label %second

second:
  br i1 %cmp, label %ibr, label %exit ; cmp must be false to reach this, branch to ibr never taken

ibr: ; this block is dead
  indirectbr ptr blockaddress(@foo, %exit), [label %exit, label %exit] ; double label required, works with just one

exit:
  ret void
}

opt --passes=gvn -S minimal.ll

Related Bug: #49237

[tetzank]

Even smaller reproducer:

define void @foo() {
entry:
  br i1 false, label %ibr, label %exit

ibr: ; this block is dead
  indirectbr ptr null, [label %exit, label %exit]

exit:
  ret void
}

[hstk30-hw]

Is the same issue with #147869?
@jacobly0 @nikic