[gcc r17-2685] AArch64: Update Neoverse V2 cost model for SVE structure loads/stores

https://gcc.gnu.org/g:ad8686f649cfeca15c4334866b4403cebc5097c9

commit r17-2685-gad8686f649cfeca15c4334866b4403cebc5097c9
Author: Pengfei Li <[email protected]>
Date:   Fri Jul 17 11:45:33 2026 +0000

    AArch64: Update Neoverse V2 cost model for SVE structure loads/stores
    
    The current Neoverse V2 cost model underestimates the costs of SVE
    structure loads and stores. This can cause the vectorizer to make a
    suboptimal choice between AdvSIMD and SVE.
    
    This patch brings the cost model in line with the latest Neoverse V2
    Software Optimization Guide, which indicates that SVE structure loads
    and stores are generally more expensive than the AdvSIMD versions.
    
    Performance testing shows this change improves SPEC CPU 2026 735.ocio_r
    by ~10.8% on Neoverse V2.
    
    Bootstrapped and tested on aarch64-linux-gnu.
    
    gcc/ChangeLog:
    
            * config/aarch64/tuning_models/neoversev2.h: Update the costs
            of SVE structure loads and stores.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.target/aarch64/sve/cost_model_20.c: New test.

Diff:
---
 gcc/config/aarch64/tuning_models/neoversev2.h      |  6 +++---
 .../gcc.target/aarch64/sve/cost_model_20.c         | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/gcc/config/aarch64/tuning_models/neoversev2.h b/gcc/config/aarch64/tuning_models/neoversev2.h
index 15eff2807f77..6df0cc444b80 100644
--- a/gcc/config/aarch64/tuning_models/neoversev2.h
+++ b/gcc/config/aarch64/tuning_models/neoversev2.h
@@ -70,9 +70,9 @@ static const sve_vec_cost neoversev2_sve_vector_cost =
   {
     2, /* int_stmt_cost  */
     2, /* fp_stmt_cost  */
-    2, /* ld2_st2_permute_cost  */
-    3, /* ld3_st3_permute_cost  */
-    3, /* ld4_st4_permute_cost  */
+    3, /* ld2_st2_permute_cost  */
+    4, /* ld3_st3_permute_cost  */
+    4, /* ld4_st4_permute_cost  */
     2, /* permute_cost  */
     /* Theoretically, a reduction involving 15 scalar ADDs could
        complete in ~5 cycles and would have a cost of 15.  [SU]ADDV
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/cost_model_20.c b/gcc/testsuite/gcc.target/aarch64/sve/cost_model_20.c
new file mode 100644
index 000000000000..77cb00cf1d60
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/cost_model_20.c
@@ -0,0 +1,22 @@
+/* { dg-options "-O3 -mtune=neoverse-v2" } */
+
+void
+f (float *restrict in, float *restrict out, int num)
+{
+  for (int i = 0; i < num; ++i)
+    {
+      float r = in[4 * i];
+      float g = in[4 * i + 1];
+      float b = in[4 * i + 2];
+      float a = in[4 * i + 3];
+      out[4 * i] = r * 0.9f + g * 1.0f + b * 0.7f + a * 1.0f;
+      out[4 * i + 1] = r * 1.1f + g * 0.8f + b * 1.2f + a * 1.0f;
+      out[4 * i + 2] = r * 0.7f + g * 1.2f + b * 0.8f + a * 1.0f;
+      out[4 * i + 3] = r * 1.2f + g * 0.7f + b * 1.1f + a * 1.0f;
+    }
+}
+
+/* We should use AdvSIMD ld4/st4 rather than SVE for the vectorized main loop
+   on Neoverse-V2.  */
+/* { dg-final { scan-assembler {\tld4\t} } } */
+/* { dg-final { scan-assembler {\tst4\t} } } */