[PATCH] target/arm: Speed up aarch64 TBL/TBX

* [PATCH] target/arm: Speed up aarch64 TBL/TBX
@ 2021-02-24 22:44 Richard Henderson
  2021-02-25  8:22 ` Alex Bennée
  0 siblings, 1 reply; 2+ messages in thread
From: Richard Henderson @ 2021-02-24 22:44 UTC (permalink / raw)
  To: qemu-devel; +Cc: qemu-arm, alex.bennee

Always perform one call instead of two for 16-byte operands.
Use byte loads/stores directly into the vector register file
instead of extractions and deposits to a 64-bit local variable.

In order to easily receive pointers into the vector register file,
convert the helper to the gvec out-of-line signature.  Move the
helper into vec_helper.c, where it can make use of H1 and clear_tail.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---

Alex, as briefly discussed on IRC today, streamline the TBL/TBX
implementation.  Would you run this through whatever benchmark
you were experimenting with today?  This is unmeasureable in RISU
(exactly one perf hit in the helper through the entire run).

r~

---
 target/arm/helper-a64.h    |  2 +-
 target/arm/helper-a64.c    | 32 ---------------------
 target/arm/translate-a64.c | 58 +++++---------------------------------
 target/arm/vec_helper.c    | 52 ++++++++++++++++++++++++++++++++++
 4 files changed, 60 insertions(+), 84 deletions(-)

diff --git a/target/arm/helper-a64.h b/target/arm/helper-a64.h
index 7bd6aed659..c139fa81f9 100644
--- a/target/arm/helper-a64.h
+++ b/target/arm/helper-a64.h
@@ -28,7 +28,7 @@ DEF_HELPER_3(vfp_cmps_a64, i64, f32, f32, ptr)
 DEF_HELPER_3(vfp_cmpes_a64, i64, f32, f32, ptr)
 DEF_HELPER_3(vfp_cmpd_a64, i64, f64, f64, ptr)
 DEF_HELPER_3(vfp_cmped_a64, i64, f64, f64, ptr)
-DEF_HELPER_FLAGS_5(simd_tbl, TCG_CALL_NO_RWG_SE, i64, env, i64, i64, i32, i32)
+DEF_HELPER_FLAGS_4(simd_tblx, TCG_CALL_NO_RWG, void, ptr, ptr, ptr, i32)
 DEF_HELPER_FLAGS_3(vfp_mulxs, TCG_CALL_NO_RWG, f32, f32, f32, ptr)
 DEF_HELPER_FLAGS_3(vfp_mulxd, TCG_CALL_NO_RWG, f64, f64, f64, ptr)
 DEF_HELPER_FLAGS_3(neon_ceq_f64, TCG_CALL_NO_RWG, i64, i64, i64, ptr)
diff --git a/target/arm/helper-a64.c b/target/arm/helper-a64.c
index 7f56c78fa6..061c8ff846 100644
--- a/target/arm/helper-a64.c
+++ b/target/arm/helper-a64.c
@@ -179,38 +179,6 @@ float64 HELPER(vfp_mulxd)(float64 a, float64 b, void *fpstp)
     return float64_mul(a, b, fpst);
 }
 
-uint64_t HELPER(simd_tbl)(CPUARMState *env, uint64_t result, uint64_t indices,
-                          uint32_t rn, uint32_t numregs)
-{
-    /* Helper function for SIMD TBL and TBX. We have to do the table
-     * lookup part for the 64 bits worth of indices we're passed in.
-     * result is the initial results vector (either zeroes for TBL
-     * or some guest values for TBX), rn the register number where
-     * the table starts, and numregs the number of registers in the table.
-     * We return the results of the lookups.
-     */
-    int shift;
-
-    for (shift = 0; shift < 64; shift += 8) {
-        int index = extract64(indices, shift, 8);
-        if (index < 16 * numregs) {
-            /* Convert index (a byte offset into the virtual table
-             * which is a series of 128-bit vectors concatenated)
-             * into the correct register element plus a bit offset
-             * into that element, bearing in mind that the table
-             * can wrap around from V31 to V0.
-             */
-            int elt = (rn * 2 + (index >> 3)) % 64;
-            int bitidx = (index & 7) * 8;
-            uint64_t *q = aa64_vfp_qreg(env, elt >> 1);
-            uint64_t val = extract64(q[elt & 1], bitidx, 8);
-
-            result = deposit64(result, shift, 8, val);
-        }
-    }
-    return result;
-}
-
 /* 64bit/double versions of the neon float compare functions */
 uint64_t HELPER(neon_ceq_f64)(float64 a, float64 b, void *fpstp)
 {
diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index b23a8975d5..496e14688a 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -7520,10 +7520,8 @@ static void disas_simd_tb(DisasContext *s, uint32_t insn)
     int rm = extract32(insn, 16, 5);
     int rn = extract32(insn, 5, 5);
     int rd = extract32(insn, 0, 5);
-    int is_tblx = extract32(insn, 12, 1);
-    int len = extract32(insn, 13, 2);
-    TCGv_i64 tcg_resl, tcg_resh, tcg_idx;
-    TCGv_i32 tcg_regno, tcg_numregs;
+    int is_tbx = extract32(insn, 12, 1);
+    int len = (extract32(insn, 13, 2) + 1) * 16;
 
     if (op2 != 0) {
         unallocated_encoding(s);
@@ -7534,53 +7532,11 @@ static void disas_simd_tb(DisasContext *s, uint32_t insn)
         return;
     }
 
-    /* This does a table lookup: for every byte element in the input
-     * we index into a table formed from up to four vector registers,
-     * and then the output is the result of the lookups. Our helper
-     * function does the lookup operation for a single 64 bit part of
-     * the input.
-     */
-    tcg_resl = tcg_temp_new_i64();
-    tcg_resh = NULL;
-
-    if (is_tblx) {
-        read_vec_element(s, tcg_resl, rd, 0, MO_64);
-    } else {
-        tcg_gen_movi_i64(tcg_resl, 0);
-    }
-
-    if (is_q) {
-        tcg_resh = tcg_temp_new_i64();
-        if (is_tblx) {
-            read_vec_element(s, tcg_resh, rd, 1, MO_64);
-        } else {
-            tcg_gen_movi_i64(tcg_resh, 0);
-        }
-    }
-
-    tcg_idx = tcg_temp_new_i64();
-    tcg_regno = tcg_const_i32(rn);
-    tcg_numregs = tcg_const_i32(len + 1);
-    read_vec_element(s, tcg_idx, rm, 0, MO_64);
-    gen_helper_simd_tbl(tcg_resl, cpu_env, tcg_resl, tcg_idx,
-                        tcg_regno, tcg_numregs);
-    if (is_q) {
-        read_vec_element(s, tcg_idx, rm, 1, MO_64);
-        gen_helper_simd_tbl(tcg_resh, cpu_env, tcg_resh, tcg_idx,
-                            tcg_regno, tcg_numregs);
-    }
-    tcg_temp_free_i64(tcg_idx);
-    tcg_temp_free_i32(tcg_regno);
-    tcg_temp_free_i32(tcg_numregs);
-
-    write_vec_element(s, tcg_resl, rd, 0, MO_64);
-    tcg_temp_free_i64(tcg_resl);
-
-    if (is_q) {
-        write_vec_element(s, tcg_resh, rd, 1, MO_64);
-        tcg_temp_free_i64(tcg_resh);
-    }
-    clear_vec_high(s, is_q, rd);
+    tcg_gen_gvec_2_ptr(vec_full_reg_offset(s, rd),
+                       vec_full_reg_offset(s, rm), cpu_env,
+                       is_q ? 16 : 8, vec_full_reg_size(s),
+                       (len << 6) | (is_tbx << 5) | rn,
+                       gen_helper_simd_tblx);
 }
 
 /* ZIP/UZP/TRN
diff --git a/target/arm/vec_helper.c b/target/arm/vec_helper.c
index 7174030377..d164273f20 100644
--- a/target/arm/vec_helper.c
+++ b/target/arm/vec_helper.c
@@ -1937,3 +1937,55 @@ DO_VRINT_RMODE(gvec_vrint_rm_h, helper_rinth, uint16_t)
 DO_VRINT_RMODE(gvec_vrint_rm_s, helper_rints, uint32_t)
 
 #undef DO_VRINT_RMODE
+
+#ifdef TARGET_AARCH64
+void HELPER(simd_tblx)(void *vd, void *vm, void *venv, uint32_t desc)
+{
+    uint64_t *d = vd;
+    const uint8_t *indices = vm;
+    CPUARMState *env = venv;
+    size_t oprsz = simd_oprsz(desc);
+    uint32_t rn = extract32(desc, SIMD_DATA_SHIFT, 5);
+    bool is_tbx = extract32(desc, SIMD_DATA_SHIFT + 5, 1);
+    uint32_t table_len = desc >> (SIMD_DATA_SHIFT + 6);
+    union {
+        uint8_t b[16];
+        uint64_t d[2];
+    } result;
+
+    /*
+     * We must construct the final result in a temp, lest the output
+     * overlaps the input table.  For TBL, begin with zero; for TBX,
+     * begin with the original register contents.  Note that for
+     * oprsz == 8, we always clear the balance of the register.
+     */
+    if (is_tbx) {
+        uint64_t d1 = d[1];
+        result.d[0] = d[0];
+        result.d[1] = oprsz == 8 ? 0 : d1;
+    } else {
+        result.d[0] = 0;
+        result.d[1] = 0;
+    }
+
+    for (size_t i = 0; i < oprsz; ++i) {
+        uint32_t index = indices[H1(i)];
+
+        if (index < table_len) {
+            /*
+             * Convert index (a byte offset into the virtual table
+             * which is a series of 128-bit vectors concatenated)
+             * into the correct register element, bearing in mind
+             * that the table can wrap around from V31 to V0.
+             */
+            const uint8_t *table = (const uint8_t *)
+                aa64_vfp_qreg(env, (rn + (index >> 4)) % 32);
+            result.b[H1(i)] = table[H1(index % 16)];
+        }
+    }
+
+    d[0] = result.d[0];
+    d[1] = result.d[1];
+    clear_tail(d, 16, simd_maxsz(desc));
+}
+#endif
-- 
2.25.1



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