Extended Description

Pulled from bullet source code:

unsigned btSelect(unsigned condition, unsigned valueIfConditionNonZero, unsigned valueIfConditionZero)
{
// Set testNz to 0xFFFFFFFF if condition is nonzero, 0x00000000 if condition is zero
// Rely on positive value or'ed with its negative having sign bit on
// and zero value or'ed with its negative (which is still zero) having sign bit off
// Use arithmetic shift right, shifting the sign bit through all 32 bits
unsigned testNz = (unsigned)(((int)condition | -(int)condition) >> 31);
unsigned testEqz = ~testNz;
return ((valueIfConditionNonZero & testNz) | (valueIfConditionZero & testEqz));
}

https://c.godbolt.org/z/rMf6Ta613

The following code doesn't get simplified:

define i8 @​src(i8 %a0, i8 %a1, i8 %a2) {
%add = add i8 %a0, -1
%xor = xor i8 %a0, -1
%and = and i8 %add, %xor
%cmp = icmp sgt i8 %and, -1
%sel = select i1 %cmp, i8 %a1, i8 %a2
ret i8 %sel
}

define i8 @​tgt(i8 %a0, i8 %a1, i8 %a2) {
%cmp = icmp ne i8 %a0, 0
%sel = select i1 %cmp, i8 %a1, i8 %a2
ret i8 %sel
}

Transformation seems to be correct!