[polly] r304074 - Allow side-effect free function calls in valid affine SCEVs

[Tobias Grosser via llvm-commits]

On Wed, May 31, 2017, at 01:31 PM, Michael Kruse via llvm-commits wrote:
> 2017-05-31 11:57 GMT+02:00 Tobias Grosser <tobias at grosser.es>:
> > On Tue, May 30, 2017, at 12:16 AM, Michael Kruse via llvm-commits wrote:
> >> 2017-05-27 17:18 GMT+02:00 Tobias Grosser via llvm-commits
> >> <llvm-commits at lists.llvm.org>:
> >> > Author: grosser
> >> > Date: Sat May 27 10:18:46 2017
> >> > New Revision: 304074
> >> >
> >> > URL: http://llvm.org/viewvc/llvm-project?rev=304074&view=rev
> >> > Log:
> >> > Allow side-effect free function calls in valid affine SCEVs
> >> >
> >> > Side-effect free function calls with only constant parameters can be easily
> >> > re-generated and consequently do not prevent us from modeling a SCEV. This
> >> > change allows array subscripts to reference function calls such as
> >> > 'get_global_id()' as used in OpenCL.
> >> >
> >> > We use the function name plus the constant operands to name the parameter. This
> >> > is possible as the function name is required and is not dropped in release
> >> > builds the same way names of llvm::Values are dropped. We also provide more
> >> > readable names for common OpenCL functions, to make it easy to understand the
> >> > polyhedral model we generate.
> >> >
> >> > Added:
> >> >     polly/trunk/test/ScopInfo/constant_functions_as_unknowns.ll
> >> > Modified:
> >> >     polly/trunk/include/polly/Support/SCEVValidator.h
> >> >     polly/trunk/lib/Analysis/ScopInfo.cpp
> >> >     polly/trunk/lib/Support/SCEVValidator.cpp
> >> >
> >> > Modified: polly/trunk/include/polly/Support/SCEVValidator.h
> >> > URL: http://llvm.org/viewvc/llvm-project/polly/trunk/include/polly/Support/SCEVValidator.h?rev=304074&r1=304073&r2=304074&view=diff
> >> > ==============================================================================
> >> > --- polly/trunk/include/polly/Support/SCEVValidator.h (original)
> >> > +++ polly/trunk/include/polly/Support/SCEVValidator.h Sat May 27 10:18:46 2017
> >> > @@ -23,9 +23,19 @@ class ScalarEvolution;
> >> >  class Value;
> >> >  class Loop;
> >> >  class LoadInst;
> >> > +class CallInst;
> >> >  } // namespace llvm
> >> >
> >> >  namespace polly {
> >> > +
> >> > +/// Check if a call is side-effect free and has only constant arguments.
> >> > +///
> >> > +/// Such calls can be re-generated easily, so we do not need to model them
> >> > +/// as scalar dependences.
> >> > +///
> >> > +/// @param Call The call to check.
> >> > +bool isConstCall(llvm::CallInst *Call);
> >> > +
> >> >  /// Find the loops referenced from a SCEV expression.
> >> >  ///
> >> >  /// @param Expr The SCEV expression to scan for loops.
> >> >
> >> > Modified: polly/trunk/lib/Analysis/ScopInfo.cpp
> >> > URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Analysis/ScopInfo.cpp?rev=304074&r1=304073&r2=304074&view=diff
> >> > ==============================================================================
> >> > --- polly/trunk/lib/Analysis/ScopInfo.cpp (original)
> >> > +++ polly/trunk/lib/Analysis/ScopInfo.cpp Sat May 27 10:18:46 2017
> >> > @@ -1998,16 +1998,50 @@ const SCEV *Scop::getRepresentingInvaria
> >> >    return SCEVSensitiveParameterRewriter::rewrite(S, *SE, InvEquivClassVMap);
> >> >  }
> >> >
> >> > +// This table of function names is used to translate parameter names in more
> >> > +// human-readable names. This makes it easier to interpret Polly analysis
> >> > +// results.
> >> > +StringMap<std::string> KnownNames = {
> >> > +    {"_Z13get_global_idj", "global_id"},
> >> > +    {"_Z12get_local_idj", "local_id"},
> >> > +    {"_Z15get_global_sizej", "global_size"},
> >> > +    {"_Z14get_local_sizej", "local_size"},
> >> > +    {"_Z12get_work_dimv", "work_dim"},
> >> > +    {"_Z17get_global_offsetj", "global_offset"},
> >> > +    {"_Z12get_group_idj", "group_id"},
> >> > +    {"_Z14get_num_groupsj", "num_groups"},
> >> > +};
> >>
> >> This is platform dependent (Itanium name mangling).
> >
> > Right. It is mostly for me (and others) to see more readable output, but
> > it does not carry semantics. So it does not hurt a lot in case it won't
> > apply on other platforms. Also, are there platforms for OpenCL which do
> > not use Itanium name mangeling?
> 
> OpenCL has not concept of linking, therefore name mangling does not
> need to be defined.
> 
> That said, SPIR [1] and SPIR-V [2] define Itanium mangling used for
> builtins. In this case however, only how clang does it seems relevant.
> Do you where the function calls a inserted and which part of
> LLVM/clang mangles it?

clang/5.0.0/include/opencl-c.h

The functions are defined as
https://clang.llvm.org/docs/AttributeReference.html#overloadable
and are consequently mangeled.

> +  auto Iterator = KnownNames.find(Name);
> +  if (Iterator != KnownNames.end())
> +    Name = "__" + KnownNames[Name];
> 
> Why does this do a second lookup instead of using the already found
> iterator result?

Resolved in r304410.

Best,
tobias