swap select operands and reuse existing inverted condition

[rotateright]

Bugzilla Link	41113
Version	trunk
OS	All
CC	@RKSimon

Extended Description

I'm not sure if there's an existing pass that should have responsibility for this transform:

define i1 @​swapportunity(i8 %a, i8 %b, i8 %c, i8 %d, i8* %p) {
%cmp1 = icmp ult i8 %a, %b
%sel = select i1 %cmp1, i8 %c, i8 %d
store i8 %sel, i8* %p
%cmp2 = icmp uge i8 %a, %b ; this could also be a 'not' of cmp1
ret i1 %cmp2
}

-->

define i1 @​swapportunity(i8 %a, i8 %b, i8 %c, i8 %d, i8* %p) {
%cmp2 = icmp uge i8 %a, %b
%swap = select i1 %cmp2, i8 %d, i8 %c
store i8 %swap, i8* %p
ret i1 %cmp2
}

---

It's not quite CSE or instcombine. There's precedence for a similar analysis/transform in instcombine via "swapMayExposeCSEOpportunities()", but that seems suspect to include there as this is not really a local/peephole pattern-match.