This is another step towards parity between existing select
transforms and min/max intrinsics (D98152)..
The existing 'not' folds around select are complicated, so
it's likely that we will need to enhance this, but this
should be a safe step.
This is a partial translation of the existing select-based
folds. We need to recreate several different transforms to
avoid regressions as noted in D98152.
https://alive2.llvm.org/ce/z/teuZ_J
The constant trunc/ext may not be the optimal pre-condition,
but I think that handles the common cases.
Example of Alive2 proof:
https://alive2.llvm.org/ce/z/sREeLC
This is another step towards canonicalizing to the intrinsics.
Narrowing was identified as source of potential regression for
abs(), so we need to handle this for min/max - see:
https://llvm.org/PR48816
If this is not enough, we could process intrinsics in
the trunc-driven matching in canEvaluateTruncated().
We can sink extends after min/max if they match and would
not change the sign-interpreted compare. The only combo
that doesn't work is zext+smin/smax because the zexts
could change a negative number into positive:
https://alive2.llvm.org/ce/z/D6sz6J
Sext+umax/umin works:
define i32 @src(i8 %x, i8 %y) {
%0:
%sx = sext i8 %x to i32
%sy = sext i8 %y to i32
%m = umax i32 %sx, %sy
ret i32 %m
}
=>
define i32 @tgt(i8 %x, i8 %y) {
%0:
%m = umax i8 %x, %y
%r = sext i8 %m to i32
ret i32 %r
}
Transformation seems to be correct!
Sanjay Patel