Re: RFC: Patch to allow use of DECL_NAME in libmvec calls instead of DECL_ASSEMBER_NAME

[Steve Ellcey]

On Tue, 2019-03-12 at 14:17 +0000, Joseph Myers wrote:
> 
> On Tue, 12 Mar 2019, Richard Biener wrote:
> 
> > It shouldn't be difficult to provide an alias from the glibc side, no?  
> > How does x86 avoid this issue?
> 
> There are static-only wrappers in libmvec_nonshared.a to work around the 
> GCC limitation (not included in the shared library, so less efficient than 
> direct calls to the vectorized functions, because it ought not be 
> necessary to have multiple symbols for the same function exported from the 
> shared library for this purpose).
> 
> The issue is as I said in 
> <https://gcc.gnu.org/ml/gcc/2015-06/msg00176.html> - vector and scalar 
> versions of functions should not need to be in one-to-one correspondence.  
> For example, you could add __attribute__ ((__vector_asm__ ("name"))) to 
> set the version of a function's name to be used as the basis for forming 
> vector function names, overriding the use of a name specified with asm 
> ("name") for that purpose.

I like this idea.  I have prototyped something, I created 'vector_asm'
as an aarch64 attribute because I couldn't find where to put global
attributes like __simd__.  Does anyone know where these are listed?
I left off the leading/trailing underscores because GCC didn't like
them in a target attribute.

I then updated my sysdeps/aarch64/fpu/bits/math-vector.h file in glibc
and things seemed to work fine.  Here are my changes, what do people
think about changing GCC to do this?

The GCC changes I made are:


diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index b38505b..45fde16 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -1180,8 +1180,9 @@ static const struct attribute_spec 
aarch64_attribute_table[] =
 {
   /* { name, min_len, max_len, decl_req, type_req, fn_type_req,
        affects_type_identity, handler, exclude } */
-  { "aarch64_vector_pcs", 0, 0, false, true,  true,  true,  NULL, NULL },
-  { NULL,                 0, 0, false, false, false, false, NULL, NULL }
+  { "aarch64_vector_pcs", 0,  0, false, true,  true,  true,  NULL, NULL },
+  { "vector_asm",         1,  1, true,  false, false, false, NULL, NULL },
+  { NULL,                 0,  0, false, false, false, false, NULL, NULL }
 };
 
 #define AARCH64_CPU_DEFAULT_FLAGS ((selected_cpu) ? selected_cpu->flags : 0)
diff --git a/gcc/omp-simd-clone.c b/gcc/omp-simd-clone.c
index 388198b..59183f0 100644
--- a/gcc/omp-simd-clone.c
+++ b/gcc/omp-simd-clone.c
@@ -342,6 +342,8 @@ simd_clone_mangle (struct cgraph_node *node,
   unsigned int simdlen = clone_info->simdlen;
   unsigned int n;
   pretty_printer pp;
+  tree attr;
+  const char *str;
 
   gcc_assert (vecsize_mangle && simdlen);
 
@@ -409,7 +411,12 @@ simd_clone_mangle (struct cgraph_node *node,
     }
 
   pp_underscore (&pp);
-  const char *str = IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (node->decl));
+  attr = lookup_attribute ("vector_asm", DECL_ATTRIBUTES (node->decl));
+  if (attr)
+    str = TREE_STRING_POINTER (TREE_VALUE (TREE_VALUE (attr)));
+  else
+    str = IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (node->decl));
+
   if (*str == '*')
     ++str;
   pp_string (&pp, str);



The new sysdeps/aarch64/fpu/bits/math-vector.h was modified to include:

# ifdef __DECL_SIMD_AARCH64
#  undef __DECL_SIMD_exp
#  define __DECL_SIMD_exp __DECL_SIMD_AARCH64 __attribute__ ((vector_asm 
("exp")))
#  undef __DECL_SIMD_expf
#  define __DECL_SIMD_expf __DECL_SIMD_AARCH64 __attribute__ ((vector_asm 
("expf")))

# endif