Extended Description

The following unit test shows incorrect behavior regarding undef inputs:
$ opt -correlated-propagation -cvp-dont-add-nowrap-flags=false Transforms/CorrelatedValuePropagation/sub.ll

The issue is the branch on undef, which if we assume is a non-deterministic jump, leads to branch %then, which then does a 'sub nuw' on an undef (which is poison).

Possible solutions: same as in #​42617.

define i32 @​test11(* %p, i32 %i) {
%limit = load i32, * %p, align 4
%range_l#0%limit = icmp sge i32 %limit, 0
%range_h#0%limit = icmp slt i32 %limit, 2147483647
%range#0%limit = and i1 %range_l#0%limit, %range_h#0%limit
assume_non_poison i1 %range#0%limit
%within.1 = icmp slt i32 %limit, %i
%i.minus.7 = add i32 %i, 4294967289
%within.2 = icmp slt i32 %limit, %i.minus.7
%within = and i1 %within.1, %within.2
br i1 %within, label %then, label %else

%then:
%i.minus.6 = sub i32 %i, 6
ret i32 %i.minus.6

%else:
ret i32 0
}
=>
define i32 @​test11(* %p, i32 %i) {
%limit = load i32, * %p, align 4
%range_l#0%limit = icmp sge i32 %limit, 0
%range_h#0%limit = icmp slt i32 %limit, 2147483647
%range#0%limit = and i1 %range_l#0%limit, %range_h#0%limit
assume_non_poison i1 %range#0%limit
%within.1 = icmp slt i32 %limit, %i
%i.minus.7 = add i32 %i, 4294967289
%within.2 = icmp slt i32 %limit, %i.minus.7
%within = and i1 %within.1, %within.2
br i1 %within, label %then, label %else

%then:
%i.minus.6 = sub nsw nuw i32 %i, 6
ret i32 %i.minus.6

%else:
ret i32 0
}
Transformation doesn't verify!
ERROR: Target is more poisonous than source

Example:

• %p = #x2dc920000000
  i32 %i = undef

Source:
i32 %limit = #x00000000 (0)
i1 %range_l#0%limit = #x1 (1)
i1 %range_h#0%limit = #x1 (1)
i1 %range#0%limit = #x1 (1)
i1 %within.1 = undef
i32 %i.minus.7 = undef
i1 %within.2 = undef
i1 %within = undef
i32 %i.minus.6 = undef

Target:
i32 %limit = #x00000000 (0)
i1 %range_l#0%limit = #x1 (1)
i1 %range_h#0%limit = #x1 (1)
i1 %range#0%limit = #x1 (1)
i1 %within.1 = undef
i32 %i.minus.7 = undef
i1 %within.2 = undef
i1 %within = undef
i32 %i.minus.6 = poison
Source value: undef
Target value: poison