aarch64: Split vec_selects of bottom elements into simple move

In certain intrinsics use cases GCC leaves SETs of a bottom-element vec
select lying around:
        (vec_select:DI (reg:V2DI 34 v2 [orig:128 __o ] [128])
            (parallel [
                    (const_int 0 [0])
                ])))

This can be treated as a simple move in aarch64 when done between SIMD
registers for all normal widths.
These go through the aarch64_get_lane pattern.
This patch adds a splitter there to simplify these extracts to a move
that can, perhaps, be optimised a way.
Another benefit is if the destination is memory we can use a simpler STR
instruction rather than ST1-lane.

gcc/

	* config/aarch64/aarch64-simd.md (aarch64_get_lane<mode>):
	Convert to define_insn_and_split.  Split into simple move when moving
	bottom element.

gcc/testsuite/

	* gcc.target/aarch64/vdup_lane_2.c: Scan for fmov rather than
	dup.

diff --git a/gcc/config/aarch64/aarch64-simd.md b/gcc/config/aarch64/aarch64-simd.md
index 41071b668fd0982f55f9e48510403b9f50fe0f60..d7acd72bede4e9b8a006fefdb21ed34c080134f5 100644 (file)
--- a/gcc/config/aarch64/aarch64-simd.md
+++ b/gcc/config/aarch64/aarch64-simd.md
@@ -3312,7 +3312,9 @@
 ;; Lane extraction of a value, neither sign nor zero extension
 ;; is guaranteed so upper bits should be considered undefined.
 ;; RTL uses GCC vector extension indices throughout so flip only for assembly.
-(define_insn "aarch64_get_lane<mode>"
+;; Extracting lane zero is split into a simple move when it is between SIMD
+;; registers or a store.
+(define_insn_and_split "aarch64_get_lane<mode>"
   [(set (match_operand:<VEL> 0 "aarch64_simd_nonimmediate_operand" "=?r, w, Utv")
        (vec_select:<VEL>
          (match_operand:VALL_F16 1 "register_operand" "w, w, w")
@@ -3332,6 +3334,12 @@
          gcc_unreachable ();
       }
   }
+ "&& reload_completed
+  && ENDIAN_LANE_N (<nunits>, INTVAL (operands[2])) == 0"
+ [(set (match_dup 0) (match_dup 1))]
+ {
+   operands[1] = aarch64_replace_reg_mode (operands[1], <VEL>mode);
+ }
   [(set_attr "type" "neon_to_gp<q>, neon_dup<q>, neon_store1_one_lane<q>")]
 )
 

diff --git a/gcc/testsuite/gcc.target/aarch64/vdup_lane_2.c b/gcc/testsuite/gcc.target/aarch64/vdup_lane_2.c
index a49db3e963db5309c5dafc25a029ef7c557aaf3f..16f4808c1dab28b66e9ad2296feb5efb705cfaaa 100644 (file)
--- a/gcc/testsuite/gcc.target/aarch64/vdup_lane_2.c
+++ b/gcc/testsuite/gcc.target/aarch64/vdup_lane_2.c
@@ -333,7 +333,7 @@ main ()
 
 /* Asm check for vdups_lane_f32, vdups_lane_s32, vdups_lane_u32.  */
 /* Can't generate "dup s<n>, v<m>[0]" for vdups_lane_s32 and vdups_lane_u32.  */
-/* { dg-final { scan-assembler-times "dup\\ts\[0-9\]+, v\[0-9\]+\.s\\\[0\\\]" 1} } */
+/* { dg-final { scan-assembler-times {fmov\ts0, s1} 1 } } */
 /* { dg-final { scan-assembler-times "dup\\ts\[0-9\]+, v\[0-9\]+\.s\\\[1\\\]" 3 } } */
 
 /* Asm check for vdupd_lane_f64, vdupd_lane_s64, vdupd_lane_u64.  */