[ConstraintElim] Failure to eliminate cmp of usub.sat

[nikic]

https://alive2.llvm.org/ce/z/4ZG-nD

define i1 @src(i64 %index, i64 %limit) {
  %precond = icmp ult i64 %index, %limit
  call void @llvm.assume(i1 %precond)
  %sub.sat = call i64 @llvm.usub.sat.i64(i64 %index, i64 1)
  %cmp = icmp ult i64 %sub.sat, %limit
  ret i1 %cmp
}

define i1 @tgt(i64 %index, i64 %limit) {
  ret i1 true
}

I think we should be able to handle this by adding a fact that the usub.sat result is ule its first argument, similar to what we do for min/max/abs.

[llvmbot]

Hi!

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[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Nikita Popov (nikic)

https://alive2.llvm.org/ce/z/4ZG-nD ```llvm define i1 @src(i64 %index, i64 %limit) { %precond = icmp ult i64 %index, %limit call void @llvm.assume(i1 %precond) %sub.sat = call i64 @llvm.usub.sat.i64(i64 %index, i64 1) %cmp = icmp ult i64 %sub.sat, %limit ret i1 %cmp }

define i1 @tgt(i64 %index, i64 %limit) {
ret i1 true
}

I think we should be able to handle this by adding a fact that the usub.sat result is ule its first argument, similar to what we do for min/max/abs.
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