On Fri, Sep 2, 2022 at 7:24 PM Segher Boessenkool <seg...@kernel.crashing.org> wrote: > > On Fri, Sep 02, 2022 at 12:02:54PM -0500, Peter Bergner wrote: > > On 9/2/22 11:31 AM, Segher Boessenkool wrote: > > > (Did you also look at non-MMA VIEW_CONVERT_EXPR uses btw?) > > > > I did. It seemed they were all related to pointers to vectors and I > > remember > > you mentioning that as one of the reasons for using VIEW_CONVERT_EXPR over > > NOP_EXPR, so I left them alone to be safe. > > Huh? I have no idea what you mean here. > > Casting from one pointer type to another never needs it. Casting from a > scalar integer type to a pointer type not either AFAIKi. But I am not a > Gimple expert, all this might be wrong, it isn't documented anywbere :-(
NOP_EXPR is for conversions between types with the same kind (and pointer-to-integer and integer-to-pointer conversions when pointer and integer are of the same size). When used on vectors it converts the vector elements. When you want to re-interpret V4SI as V4SF you need VIEW_CONVERT_EXPR (bit_cast), likewise V4SI interpreted as V16QI needs that. Think of VIEW_CONVERT as bit_cast and NOP_EXPR as conversion. Of course for some conversions (like unsigned int to int) you can also use a VIEW_CONVERT since it's semantically the same. In those cases we canonicalize to NOP_EXPR via folding. Richard. > > > Segher
