On Wed, 24 Oct 2012, Jason Merrill wrote:
My guess for the reason why OpenCL has the semantics it does is that if you stored a boolean result in a variable earlier and then use it as the ? condition, that would require an extra comparison whereas if it's already a vector of 0 and -1 as expected it can be used directly.
I don't understand how < 0 differs from != 0 for that purpose. In both cases, the front-end will produce the extra comparison, and the middle-end will need an optimization to detect "truth values" (vectors of -1 and 0) and simplify trivial operations on those (<0, !=0, etc).
(at a point, based on Richard's words but apparently not on his suggestion, I was tempted to introduce a new boolean vector type, whose only values are 0 and -1, but that seems a bit complicated and doesn't answer whether x?y:z should mean x<0 or x!=0)
-- Marc Glisse
