On Fri, 2018-04-13 at 16:54 -0500, Segher Boessenkool wrote: > Hi Carl, > > On Fri, Apr 13, 2018 at 09:49:25AM -0700, Carl Love wrote: > > diff --git a/gcc/config/rs6000/rs6000.c > > b/gcc/config/rs6000/rs6000.c > > index a0c9b5c..855be43 100644 > > --- a/gcc/config/rs6000/rs6000.c > > +++ b/gcc/config/rs6000/rs6000.c > > @@ -16576,8 +16576,9 @@ rs6000_gimple_fold_builtin > > (gimple_stmt_iterator *gsi) > > { > > arg0 = gimple_call_arg (stmt, 0); > > lhs = gimple_call_lhs (stmt); > > - /* Only fold the vec_splat_*() if arg0 is constant. */ > > - if (TREE_CODE (arg0) != INTEGER_CST) > > + /* Only fold the vec_splat_*() if arg0 is a 5-bit > > constant. */ > > + if (TREE_CODE (arg0) != INTEGER_CST > > + || TREE_INT_CST_LOW (arg0) & ~0x1f) > > return false; > > Should this test for *signed* 5-bit constants only? > > if (TREE_CODE (arg0) != INTEGER_CST > || !IN_RANGE (TREE_INT_CST_LOW (arg0), -16, 15)) Segher:
The buitins for the unsigned vec_splat_u[8, 16,32] are actually mapped to their corresponding signed version vec_splat_s[8, 16,32] in altivec.h. Both the vec_splat_u[8, 16,32] and vec_splat_s[8, 16,32] builtins will get you to the case statement /* flavors of vec_splat_[us]{8,16,32}. */ case ALTIVEC_BUILTIN_VSPLTISB: case ALTIVEC_BUILTIN_VSPLTISH: case ALTIVEC_BUILTIN_VSPLTISW: under which the change is being made. So technically arg0 could be a signed 5-bit or an unsiged 5-bit value. Either way the 5-bit value is splatted into the vector with sign extension to 8/16/32 bits. So I would argue that the IN_RANGE test for signed values is maybe misleading as arg0 could represent a signed or unsigned value. Both tests, the one from the patch or Segher's suggestion, are really just looking to see if any of the upper bits are 1. From a functional standpoint, I don't see any difference and feel either one would do the job. Am I missing anything? Carl Love