[PATCH, rs6000] Fold vector shifts in GIMPLE

[Bill Schmidt]

> On Jun 1, 2017, at 2:48 AM, Richard Biener <richard.guenther@gmail.com> wrote:
> 
> On Wed, May 31, 2017 at 10:01 PM, Will Schmidt
> <will_schmidt@vnet.ibm.com> wrote:
>> Hi,
>> 
>> Add support for early expansion of vector shifts.  Including
>> vec_sl (shift left), vec_sr (shift right), vec_sra (shift
>> right algebraic), vec_rl (rotate left).
>> Part of this includes adding the vector shift right instructions to
>> the list of those instructions having an unsigned second argument.
>> 
>> The VSR (vector shift right) folding is a bit more complex than
>> the others. This is due to requiring arg0 be unsigned for an algebraic
>> shift before the gimple RSHIFT_EXPR assignment is built.
> 
> Jakub, do we sanitize that undefinedness of left shifts of negative values
> and/or overflow of left shift of nonnegative values?
> 
> Will, how is that defined in the intrinsics operation?  It might need similar
> treatment as the abs case.

Answering for Will -- vec_sl is defined to simply shift bits off the end to the
left and fill with zeros from the right, regardless of whether the source type
is signed or unsigned.  The result type is signed iff the source type is
signed.  So a negative value can become positive as a result of the
operation.

The same is true of vec_rl, which will naturally rotate bits regardless of 
signedness.

Old but reliable reference:
http://www.nxp.com/assets/documents/data/en/reference-manuals/ALTIVECPIM.pdf

Bill

> 
> [I'd rather make the negative left shift case implementation defined
> given C and C++ standards
> do not agree to 100% AFAIK]
> 
> Richard.
> 
>> [gcc]
>> 
>> 2017-05-26  Will Schmidt  <will_schmidt@vnet.ibm.com>
>> 
>>        * config/rs6000/rs6000.c (rs6000_gimple_fold_builtin): Add handling
>>        for early expansion of vector shifts (sl,sr,sra,rl).
>>        (builtin_function_type): Add vector shift right instructions
>>        to the unsigned argument list.
>> 
>> [gcc/testsuite]
>> 
>> 2017-05-26  Will Schmidt  <will_schmidt@vnet.ibm.com>
>> 
>>        * testsuite/gcc.target/powerpc/fold-vec-shift-char.c: New.
>>        * testsuite/gcc.target/powerpc/fold-vec-shift-int.c: New.
>>        * testsuite/gcc.target/powerpc/fold-vec-shift-longlong.c: New.
>>        * testsuite/gcc.target/powerpc/fold-vec-shift-short.c: New.
>> 
>> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
>> index 8adbc06..6ee0bfd 100644
>> --- a/gcc/config/rs6000/rs6000.c
>> +++ b/gcc/config/rs6000/rs6000.c
>> @@ -17408,6 +17408,76 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
>>        gsi_replace (gsi, g, true);
>>        return true;
>>       }
>> +    /* Flavors of vec_rotate_left . */
>> +    case ALTIVEC_BUILTIN_VRLB:
>> +    case ALTIVEC_BUILTIN_VRLH:
>> +    case ALTIVEC_BUILTIN_VRLW:
>> +    case P8V_BUILTIN_VRLD:
>> +      {
>> +       arg0 = gimple_call_arg (stmt, 0);
>> +       arg1 = gimple_call_arg (stmt, 1);
>> +       lhs = gimple_call_lhs (stmt);
>> +       gimple *g = gimple_build_assign (lhs, LROTATE_EXPR, arg0, arg1);
>> +       gimple_set_location (g, gimple_location (stmt));
>> +       gsi_replace (gsi, g, true);
>> +       return true;
>> +      }
>> +  /* Flavors of vector shift right algebraic.  vec_sra{b,h,w} -> vsra{b,h,w}. */
>> +    case ALTIVEC_BUILTIN_VSRAB:
>> +    case ALTIVEC_BUILTIN_VSRAH:
>> +    case ALTIVEC_BUILTIN_VSRAW:
>> +    case P8V_BUILTIN_VSRAD:
>> +      {
>> +       arg0 = gimple_call_arg (stmt, 0);
>> +       arg1 = gimple_call_arg (stmt, 1);
>> +       lhs = gimple_call_lhs (stmt);
>> +       gimple *g = gimple_build_assign (lhs, RSHIFT_EXPR, arg0, arg1);
>> +       gimple_set_location (g, gimple_location (stmt));
>> +       gsi_replace (gsi, g, true);
>> +       return true;
>> +      }
>> +   /* Flavors of vector shift left.  builtin_altivec_vsl{b,h,w} -> vsl{b,h,w}.  */
>> +    case ALTIVEC_BUILTIN_VSLB:
>> +    case ALTIVEC_BUILTIN_VSLH:
>> +    case ALTIVEC_BUILTIN_VSLW:
>> +    case P8V_BUILTIN_VSLD:
>> +      {
>> +       arg0 = gimple_call_arg (stmt, 0);
>> +       arg1 = gimple_call_arg (stmt, 1);
>> +       lhs = gimple_call_lhs (stmt);
>> +       gimple *g = gimple_build_assign (lhs, LSHIFT_EXPR, arg0, arg1);
>> +       gimple_set_location (g, gimple_location (stmt));
>> +       gsi_replace (gsi, g, true);
>> +       return true;
>> +      }
>> +    /* Flavors of vector shift right. */
>> +    case ALTIVEC_BUILTIN_VSRB:
>> +    case ALTIVEC_BUILTIN_VSRH:
>> +    case ALTIVEC_BUILTIN_VSRW:
>> +    case P8V_BUILTIN_VSRD:
>> +      {
>> +       arg0 = gimple_call_arg (stmt, 0);
>> +       arg1 = gimple_call_arg (stmt, 1);
>> +       lhs = gimple_call_lhs (stmt);
>> +       gimple *g;
>> +       /* convert arg0 to unsigned */
>> +       arg0 = convert(unsigned_type_for(TREE_TYPE(arg0)),arg0);
>> +       tree arg0_uns = create_tmp_reg_or_ssa_name(unsigned_type_for(TREE_TYPE(arg0)));
>> +       g = gimple_build_assign(arg0_uns,arg0);
>> +       gimple_set_location (g, gimple_location (stmt));
>> +       gsi_insert_before (gsi, g, GSI_SAME_STMT);
>> +       /* convert lhs to unsigned and do the shift.  */
>> +       tree lhs_uns = create_tmp_reg_or_ssa_name(unsigned_type_for(TREE_TYPE(lhs)));
>> +       g = gimple_build_assign (lhs_uns, RSHIFT_EXPR, arg0_uns, arg1);
>> +       gimple_set_location (g, gimple_location (stmt));
>> +       gsi_insert_before (gsi, g, GSI_SAME_STMT);
>> +       /* convert lhs back to a signed type for the return. */
>> +       lhs_uns = convert(signed_type_for(TREE_TYPE(lhs)),lhs_uns);
>> +       g = gimple_build_assign(lhs,lhs_uns);
>> +       gimple_set_location (g, gimple_location (stmt));
>> +       gsi_replace (gsi, g, true);
>> +       return true;
>> +      }
>>     default:
>>       break;
>>     }
>> @@ -19128,6 +19198,14 @@ builtin_function_type (machine_mode mode_ret, machine_mode mode_arg0,
>>       h.uns_p[2] = 1;
>>       break;
>> 
>> +       /* unsigned second arguments (vector shift right).  */
>> +    case ALTIVEC_BUILTIN_VSRB:
>> +    case ALTIVEC_BUILTIN_VSRH:
>> +    case ALTIVEC_BUILTIN_VSRW:
>> +    case P8V_BUILTIN_VSRD:
>> +      h.uns_p[2] = 1;
>> +      break;
>> +
>>     default:
>>       break;
>>     }
>> diff --git a/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-char.c b/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-char.c
>> new file mode 100644
>> index 0000000..ebe91e7
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-char.c
>> @@ -0,0 +1,66 @@
>> +/* Verify that overloaded built-ins for vec_sl with char
>> +   inputs produce the right results.  */
>> +
>> +/* { dg-do compile } */
>> +/* { dg-require-effective-target powerpc_altivec_ok } */
>> +/* { dg-options "-maltivec -O2" } */
>> +
>> +#include <altivec.h>
>> +
>> +//# vec_sl  - shift left
>> +//# vec_sr  - shift right
>> +//# vec_sra - shift right algebraic
>> +//# vec_rl  - rotate left
>> +
>> +vector signed char
>> +testsl_signed (vector signed char x, vector unsigned char y)
>> +{
>> +  return vec_sl (x, y);
>> +}
>> +
>> +vector unsigned char
>> +testsl_unsigned (vector unsigned char x, vector unsigned char y)
>> +{
>> +  return vec_sl (x, y);
>> +}
>> +
>> +vector signed char
>> +testsr_signed (vector signed char x, vector unsigned char y)
>> +{
>> +  return vec_sr (x, y);
>> +}
>> +
>> +vector unsigned char
>> +testsr_unsigned (vector unsigned char x, vector unsigned char y)
>> +{
>> +  return vec_sr (x, y);
>> +}
>> +
>> +vector signed char
>> +testsra_signed (vector signed char x, vector unsigned char y)
>> +{
>> +  return vec_sra (x, y);
>> +}
>> +
>> +vector unsigned char
>> +testsra_unsigned (vector unsigned char x, vector unsigned char y)
>> +{
>> +  return vec_sra (x, y);
>> +}
>> +
>> +vector signed char
>> +testrl_signed (vector signed char x, vector unsigned char y)
>> +{
>> +  return vec_rl (x, y);
>> +}
>> +
>> +vector unsigned char
>> +testrl_unsigned (vector unsigned char x, vector unsigned char y)
>> +{
>> +  return vec_rl (x, y);
>> +}
>> +
>> +/* { dg-final { scan-assembler-times "vslb" 2 } } */
>> +/* { dg-final { scan-assembler-times "vsrb" 2 } } */
>> +/* { dg-final { scan-assembler-times "vsrab" 2 } } */
>> +/* { dg-final { scan-assembler-times "vrlb" 2 } } */
>> diff --git a/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-int.c b/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-int.c
>> new file mode 100644
>> index 0000000..e9c5fe1
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-int.c
>> @@ -0,0 +1,61 @@
>> +/* Verify that overloaded built-ins for vec_sl with int
>> +   inputs produce the right results.  */
>> +
>> +/* { dg-do compile } */
>> +/* { dg-require-effective-target powerpc_altivec_ok } */
>> +/* { dg-options "-maltivec -O2" } */
>> +
>> +#include <altivec.h>
>> +
>> +vector signed int
>> +testsl_signed (vector signed int x, vector unsigned int y)
>> +{
>> +  return vec_sl (x, y);
>> +}
>> +
>> +vector unsigned int
>> +testsl_unsigned (vector unsigned int x, vector unsigned int y)
>> +{
>> +  return vec_sl (x, y);
>> +}
>> +
>> +vector signed int
>> +testsr_signed (vector signed int x, vector unsigned int y)
>> +{
>> +  return vec_sr (x, y);
>> +}
>> +
>> +vector unsigned int
>> +testsr_unsigned (vector unsigned int x, vector unsigned int y)
>> +{
>> +  return vec_sr (x, y);
>> +}
>> +
>> +vector signed int
>> +testsra_signed (vector signed int x, vector unsigned int y)
>> +{
>> +  return vec_sra (x, y);
>> +}
>> +
>> +vector unsigned int
>> +testsra_unsigned (vector unsigned int x, vector unsigned int y)
>> +{
>> +  return vec_sra (x, y);
>> +}
>> +
>> +vector signed int
>> +testrl_signed (vector signed int x, vector unsigned int y)
>> +{
>> +  return vec_rl (x, y);
>> +}
>> +
>> +vector unsigned int
>> +testrl_unsigned (vector unsigned int x, vector unsigned int y)
>> +{
>> +  return vec_rl (x, y);
>> +}
>> +
>> +/* { dg-final { scan-assembler-times "vslw" 2 } } */
>> +/* { dg-final { scan-assembler-times "vsrw" 2 } } */
>> +/* { dg-final { scan-assembler-times "vsraw" 2 } } */
>> +/* { dg-final { scan-assembler-times "vrlw" 2 } } */
>> diff --git a/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-longlong.c b/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-longlong.c
>> new file mode 100644
>> index 0000000..97b82cf
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-longlong.c
>> @@ -0,0 +1,63 @@
>> +/* Verify that overloaded built-ins for vec_sl with long long
>> +   inputs produce the right results.  */
>> +
>> +/* { dg-do compile } */
>> +/* { dg-require-effective-target powerpc_p8vector_ok } */
>> +/* { dg-options "-mpower8-vector -O2" } */
>> +
>> +#include <altivec.h>
>> +
>> +vector signed long long
>> +testsl_signed (vector signed long long x, vector unsigned long long y)
>> +{
>> +  return vec_sl (x, y);
>> +}
>> +
>> +vector unsigned long long
>> +testsl_unsigned (vector unsigned long long x, vector unsigned long long y)
>> +{
>> +  return vec_sl (x, y);
>> +}
>> +
>> +vector signed long long
>> +testsr_signed (vector signed long long x, vector unsigned long long y)
>> +{
>> +  return vec_sr (x, y);
>> +}
>> +
>> +vector unsigned long long
>> +testsr_unsigned (vector unsigned long long x, vector unsigned long long y)
>> +{
>> +  return vec_sr (x, y);
>> +}
>> +
>> +vector signed long long
>> +testsra_signed (vector signed long long x, vector unsigned long long y)
>> +{
>> +  return vec_sra (x, y);
>> +}
>> +
>> +/* watch for PR 79544 here (vsrd / vsrad issue) */
>> +vector unsigned long long
>> +testsra_unsigned (vector unsigned long long x, vector unsigned long long y)
>> +{
>> +  return vec_sra (x, y);
>> +}
>> +
>> +vector signed long long
>> +testrl_signed (vector signed long long x, vector unsigned long long y)
>> +{
>> +  return vec_rl (x, y);
>> +}
>> +
>> +vector unsigned long long
>> +testrl_unsigned (vector unsigned long long x, vector unsigned long long y)
>> +{
>> +  return vec_rl (x, y);
>> +}
>> +
>> +/* { dg-final { scan-assembler-times "vsld" 2 } } */
>> +/* { dg-final { scan-assembler-times "vsrd" 2 } } */
>> +/* { dg-final { scan-assembler-times "vsrad" 2 } } */
>> +/* { dg-final { scan-assembler-times "vrld" 2 } } */
>> +
>> diff --git a/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-short.c b/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-short.c
>> new file mode 100644
>> index 0000000..4ca7c18
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/powerpc/fold-vec-shift-short.c
>> @@ -0,0 +1,61 @@
>> +/* Verify that overloaded built-ins for vec_sl with short
>> +   inputs produce the right results.  */
>> +
>> +/* { dg-do compile } */
>> +/* { dg-require-effective-target powerpc_altivec_ok } */
>> +/* { dg-options "-maltivec -O2" } */
>> +
>> +#include <altivec.h>
>> +
>> +vector signed short
>> +testsl_signed (vector signed short x, vector unsigned short y)
>> +{
>> +  return vec_sl (x, y);
>> +}
>> +
>> +vector unsigned short
>> +testsl_unsigned (vector unsigned short x, vector unsigned short y)
>> +{
>> +  return vec_sl (x, y);
>> +}
>> +
>> +vector signed short
>> +testsr_signed (vector signed short x, vector unsigned short y)
>> +{
>> +  return vec_sr (x, y);
>> +}
>> +
>> +vector unsigned short
>> +testsr_unsigned (vector unsigned short x, vector unsigned short y)
>> +{
>> +  return vec_sr (x, y);
>> +}
>> +
>> +vector signed short
>> +testsra_signed (vector signed short x, vector unsigned short y)
>> +{
>> +  return vec_sra (x, y);
>> +}
>> +
>> +vector unsigned short
>> +testsra_unsigned (vector unsigned short x, vector unsigned short y)
>> +{
>> +  return vec_sra (x, y);
>> +}
>> +
>> +vector signed short
>> +testrl_signed (vector signed short x, vector unsigned short y)
>> +{
>> +  return vec_rl (x, y);
>> +}
>> +
>> +vector unsigned short
>> +testrl_unsigned (vector unsigned short x, vector unsigned short y)
>> +{
>> +  return vec_rl (x, y);
>> +}
>> +
>> +/* { dg-final { scan-assembler-times "vslh" 2 } } */
>> +/* { dg-final { scan-assembler-times "vsrh" 2 } } */
>> +/* { dg-final { scan-assembler-times "vsrah" 2 } } */
>> +/* { dg-final { scan-assembler-times "vrlh" 2 } } */
>> 
>> 
>> 
>