On Wed, Jul 18, 2018 at 8:08 PM Richard Sandiford <richard.sandif...@arm.com> wrote: > > This patch adds the target framework for handling the SVE ACLE, > starting with four functions: svadd, svptrue, svsub and svsubr. > > The ACLE has both overloaded and non-overloaded names. Without > the equivalent of clang's __attribute__((overloadable)), a header > file that declared all functions would need three sets of declarations: > > - the non-overloaded forms (used for both C and C++) > - _Generic-based macros to handle overloading in C > - normal overloaded inline functions for C++ > > This would likely require a lot of cut-&-paste. It would probably > also lead to poor diagnosics and be slow to parse. > > Another consideration is that some functions require certain arguments > to be integer constant expressions. We can (sort of) enforce that > for calls to built-in functions using resolve_overloaded_builtin, > but it would be harder to enforce with inline forwarder functions. > > For these reasons and others, the patch takes the approach of adding > a pragma that gets the compiler to insert the definitions itself. > This requires a slight variation on the existing lang hooks for > built-in functions, but otherwise it seems to just work.
I guess you did consider auto-generating the three variants from a template? > It was easier to add the support without enumerating every function > at build time. This in turn meant that it was easier if the SVE > builtins occupied a distinct numberspace from the existing AArch64 ones. > The patch therefore divides the built-in functions codes into "major" > and "minor" codes. At present the major code is just "general" or "SVE". > > For now, the patch is only expected to work for fixed-length SVE. > Some uses of the ACLE do manage to squeak through the front-end > in the normal vector-length agnostic mode, but that's more by > accident than design. We're planning to work on proper frontend > support for "sizeless" types in parallel with the backend changes. > > Other things not handled yet: > > - support for the SVE AAPCS > - handling the built-ins correctly when the compiler is invoked > without SVE enabled (e.g. if SVE is enabled later by a pragma) > > Both of these are blockers to merging the support into trunk. > > The aim is to make sure when adding a function that the function > produces the expected assembly output for all relevant combinations. > The patch adds a new check-function-bodies test to try to make > that easier. > > Tested on aarch64-linux-gnu (with and without SVE) and committed > to aarch64/sve-acle-branch. > > Richard > >
