assigned to @rotateright

Can you please post relevant standalone snippets here, as links to godbolt?

#include

bool test1(int x, int y){return (x<=>y)<0;}

bool test2(int x){return (x<=>1)<0;}

bool test3(int x){return (x<=>0)>0;}

bool test4(int x){return (x<=>0)<0;}

define dso_local zeroext i1 @​_Z5test1ii(i32 %0, i32 %1) local_unnamed_addr #​0 {
%3 = icmp slt i32 %0, %1
ret i1 %3
}

define dso_local zeroext i1 @​_Z5test2i(i32 %0) local_unnamed_addr #​0 {
%2 = icmp slt i32 %0, 1
ret i1 %2
}

define dso_local zeroext i1 @​_Z5test3i(i32 %0) local_unnamed_addr #​0 {
%2 = icmp sgt i32 %0, 0
ret i1 %2
}

define dso_local zeroext i1 @​_Z5test4i(i32 %0) local_unnamed_addr #​0 {
%2 = lshr i32 %0, 24
%3 = trunc i32 %2 to i8
%4 = icmp ne i32 %0, 0
%5 = icmp slt i8 %3, 0
%6 = and i1 %4, %5
ret i1 %6
}

https://godbolt.org/z/n78v1dahz

define i1 @​src(i32 %0) {
%1:
%2 = icmp slt i32 %0, 0
%3 = select i1 %2, i8 255, i8 1
%4 = icmp eq i32 %0, 0
%5 = select i1 %4, i8 0, i8 %3
%6 = icmp slt i8 %5, 0
ret i1 %6
}
=>
define i1 @​tgt(i32 %0) {
%1:
%2 = icmp slt i32 %0, 0
ret i1 %2
}
Transformation seems to be correct!

https://alive2.llvm.org/ce/z/jAqWw4

We somehow miss this transformation for SLT,
https://godbolt.org/z/8KrnKj1sh
for SGT it works now:
https://godbolt.org/z/PaKbY48Pv

Looks like we're just missing a basic icmp fold for a truncated value:
https://alive2.llvm.org/ce/z/6vQvrP

I'll post a patch.

This should get the example in the description:
https://reviews.llvm.org/rG5354a213a0e3

If there are other examples, please reopen or file more bugs. Thanks!