Re: [i386] scalar ops that preserve the high part of a vector

[Uros Bizjak <ubizjak at gmail dot com>]

On Fri, Nov 30, 2012 at 1:34 PM, Marc Glisse <marc.glisse@inria.fr> wrote:

> Hello,
>
> I experimented with the simplify-rtx transformation you suggested, see:
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54855
>
> It works when the argument is a register, but not for memory (which is where
> the constant is in the testcase). And the description of the operation in
> sse.md does seem problematic. It says the second argument is:
>
>             (match_operand:VF_128 2 "nonimmediate_operand" "xm,xm"))
>
> but Intel's documentation says "The source operand can be an XMM register or
> a 64-bit memory location", not quite the same.
>
> Do you think the .md description should really stay this way, or could we
> change it to something that better reflects "64-bit memory location"?

For reference, we are talking about:

(define_insn "<sse>_vm<plusminus_insn><mode>3"
  [(set (match_operand:VF_128 0 "register_operand" "=x,x")
	(vec_merge:VF_128
	  (plusminus:VF_128
	    (match_operand:VF_128 1 "register_operand" "0,x")
	    (match_operand:VF_128 2 "nonimmediate_operand" "xm,xm"))
	  (match_dup 1)
	  (const_int 1)))]
  "TARGET_SSE"
  "@
   <plusminus_mnemonic><ssescalarmodesuffix>\t{%2, %0|%0, %2}
   v<plusminus_mnemonic><ssescalarmodesuffix>\t{%2, %1, %0|%0, %1, %2}"
  [(set_attr "isa" "noavx,avx")
   (set_attr "type" "sseadd")
   (set_attr "prefix" "orig,vex")
   (set_attr "mode" "<ssescalarmode>")])

No, looking at your description, the operand 2 should be scalar
operand (we use _s{s,d} scalar instruction here), and for doubles this
should refer to 64bit memory location. I don't remember all the
details about vec_merge scalar instructions, but it looks to me that
canonical representation should be more like your proposal:

+(define_insn "*sse2_vm<plusminus_insn>v2df3"
+  [(set (match_operand:V2DF 0 "register_operand" "=x,x")
+    (vec_concat:V2DF
+      (plusminus:DF
+        (vec_select:DF
+          (match_operand:V2DF 1 "register_operand" "0,x")
+          (parallel [(const_int 0)]))
+        (match_operand:DF 2 "nonimmediate_operand" "xm,xm"))
+      (vec_select:DF (match_dup 1) (parallel [(const_int 1)]))))]
+  "TARGET_SSE2"

Uros.