Re: [PATCH 1/2][AArch64] Simplify patterns for sshr_n_[us]64 intrinsic

[Alan Lawrence <alan dot lawrence at arm dot com>]

Patch attached.

Alan Lawrence wrote:
> The sshr_n_64 intrinsics allow performing a signed shift right by 64 places. The 
> standard ashrdi3 pattern masks the sign amount with 63, so cannot be used. 
> However, such a shift fills the result by the sign bit, which is identical to 
> shifting right by 63. This patch just simplifies the code to shift by 63 
> instead, which allows to remove an UNSPEC and insn previously dedicated to this 
> case.
>
> Cross-tested on aarch64-none-elf and aarch64_be-none-elf, with test coverage 
> provided by gcc.target/aarch64/sshr64_1.c .
>
> gcc/ChangeLog:
>
> 	* config/aarch64/aarch64.md (enum "unspec"): Remove UNSPEC_SSHR64.
>
> 	* config/aarch64/aarch64-simd.md (aarch64_ashr_simddi): Change shift
> 	amount to 63 if was 64.
> 	(aarch64_sshr_simddi): Remove.
diff --git a/gcc/config/aarch64/aarch64-simd.md b/gcc/config/aarch64/aarch64-simd.md
index d493054b703c5698b771ce32d613e28d7c7b7b49..9cacdb1d40840952632532f5a356bbce4d611581 100644
--- a/gcc/config/aarch64/aarch64-simd.md
+++ b/gcc/config/aarch64/aarch64-simd.md
@@ -700,25 +700,16 @@
    (match_operand:SI 2 "aarch64_shift_imm64_di" "")]
   "TARGET_SIMD"
   {
+    /* An arithmetic shift right by 64 fills the result with copies of the sign
+       bit, just like asr by 63 - however the standard pattern does not handle
+       a shift by 64.  */
     if (INTVAL (operands[2]) == 64)
-      emit_insn (gen_aarch64_sshr_simddi (operands[0], operands[1]));
-    else
-      emit_insn (gen_ashrdi3 (operands[0], operands[1], operands[2]));
+      operands[2] = GEN_INT (63);
+    emit_insn (gen_ashrdi3 (operands[0], operands[1], operands[2]));
     DONE;
   }
 )
 
-;; SIMD shift by 64.  This pattern is a special case as standard pattern does
-;; not handle NEON shifts by 64.
-(define_insn "aarch64_sshr_simddi"
-  [(set (match_operand:DI 0 "register_operand" "=w")
-        (unspec:DI
-          [(match_operand:DI 1 "register_operand" "w")] UNSPEC_SSHR64))]
-  "TARGET_SIMD"
-  "sshr\t%d0, %d1, 64"
-  [(set_attr "type" "neon_shift_imm")]
-)
-
 (define_expand "vlshr<mode>3"
  [(match_operand:VQ_S 0 "register_operand" "")
   (match_operand:VQ_S 1 "register_operand" "")
diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
index 736da80b2705d02793433e6cdbcd422bfecc76f4..2b519c50360dd774298d7d97572e82e5424b843f 100644
--- a/gcc/config/aarch64/aarch64.md
+++ b/gcc/config/aarch64/aarch64.md
@@ -100,7 +100,6 @@
     UNSPEC_SISD_SSHL
     UNSPEC_SISD_USHL
     UNSPEC_SSHL_2S
-    UNSPEC_SSHR64
     UNSPEC_ST1
     UNSPEC_ST2
     UNSPEC_ST3