[src/trunk]: src/sys/net Implement BPF_ALU+BPF_MOD-BPF_K when pc->k is a powe...

[alnsn <alnsn%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/761d98faa435
branches:  trunk
changeset: 804026:761d98faa435
user:      alnsn <alnsn%NetBSD.org@localhost>
date:      Thu Nov 20 19:18:52 2014 +0000

description:
Implement BPF_ALU+BPF_MOD-BPF_K when pc->k is a power of 2. Get rid of divt
and divw arguments in emit_moddiv(), they're accessible via the pc argument.

diffstat:

 sys/net/bpfjit.c |  68 ++++++++++++++++++++++++++++++++++---------------------
 1 files changed, 42 insertions(+), 26 deletions(-)

diffs (128 lines):

diff -r 5d47929f36cc -r 761d98faa435 sys/net/bpfjit.c
--- a/sys/net/bpfjit.c  Thu Nov 20 16:34:25 2014 +0000
+++ b/sys/net/bpfjit.c  Thu Nov 20 19:18:52 2014 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: bpfjit.c,v 1.34 2014/11/20 14:35:01 alnsn Exp $        */
+/*     $NetBSD: bpfjit.c,v 1.35 2014/11/20 19:18:52 alnsn Exp $        */
 
 /*-
  * Copyright (c) 2011-2014 Alexander Nasonov.
@@ -31,9 +31,9 @@
 
 #include <sys/cdefs.h>
 #ifdef _KERNEL
-__KERNEL_RCSID(0, "$NetBSD: bpfjit.c,v 1.34 2014/11/20 14:35:01 alnsn Exp $");
+__KERNEL_RCSID(0, "$NetBSD: bpfjit.c,v 1.35 2014/11/20 19:18:52 alnsn Exp $");
 #else
-__RCSID("$NetBSD: bpfjit.c,v 1.34 2014/11/20 14:35:01 alnsn Exp $");
+__RCSID("$NetBSD: bpfjit.c,v 1.35 2014/11/20 19:18:52 alnsn Exp $");
 #endif
 
 #include <sys/types.h>
@@ -1087,25 +1087,43 @@
        return SLJIT_SUCCESS;
 }
 
+/*
+ * Emit code for A = A / k or A = A % k when k is a power of 2.
+ * @pc BPF_DIV or BPF_MOD instruction.
+ */
 static int
-emit_pow2_division(struct sljit_compiler *compiler, uint32_t k)
+emit_pow2_moddiv(struct sljit_compiler *compiler, const struct bpf_insn *pc)
 {
-       int shift = 0;
+       uint32_t k = pc->k;
        int status = SLJIT_SUCCESS;
 
-       while (k > 1) {
-               k >>= 1;
-               shift++;
-       }
+       BJ_ASSERT(k != 0 && (k & (k - 1)) == 0);
 
-       BJ_ASSERT(k == 1 && shift < 32);
-
-       if (shift != 0) {
+       if (BPF_OP(pc->code) == BPF_MOD) {
                status = sljit_emit_op2(compiler,
-                   SLJIT_LSHR|SLJIT_INT_OP,
+                   SLJIT_AND,
                    BJ_AREG, 0,
                    BJ_AREG, 0,
-                   SLJIT_IMM, shift);
+                   SLJIT_IMM, k - 1);
+       } else {
+               int shift = 0;
+
+               /*
+                * Do shift = __builtin_ctz(k).
+                * The loop is slower, but that's ok.
+                */
+               while (k > 1) {
+                       k >>= 1;
+                       shift++;
+               }
+
+               if (shift != 0) {
+                       status = sljit_emit_op2(compiler,
+                           SLJIT_LSHR|SLJIT_INT_OP,
+                           BJ_AREG, 0,
+                           BJ_AREG, 0,
+                           SLJIT_IMM, shift);
+               }
        }
 
        return status;
@@ -1128,15 +1146,15 @@
 #endif
 
 /*
- * Emit code for A = A / div or A = A % div
- * divt,divw are either SLJIT_IMM,pc->k or BJ_XREG,0.
+ * Emit code for A = A / div or A = A % div.
+ * @pc BPF_DIV or BPF_MOD instruction.
  */
 static int
-emit_moddiv(struct sljit_compiler *compiler,
-    const struct bpf_insn *pc, int divt, sljit_sw divw)
+emit_moddiv(struct sljit_compiler *compiler, const struct bpf_insn *pc)
 {
        int status;
        const bool div = BPF_OP(pc->code) == BPF_DIV;
+       const bool xreg = BPF_SRC(pc->code) == BPF_X;
 
 #if BJ_XREG == SLJIT_RETURN_REG   || \
     BJ_XREG == SLJIT_SCRATCH_REG1 || \
@@ -1157,7 +1175,8 @@
        status = sljit_emit_op1(compiler,
            SLJIT_MOV,
            SLJIT_SCRATCH_REG2, 0,
-           divt, divw);
+           xreg ? BJ_XREG : SLJIT_IMM,
+           xreg ? 0 : (uint32_t)pc->k);
        if (status != SLJIT_SUCCESS)
                return status;
 
@@ -1940,17 +1959,14 @@
                        }
 
                        if (src == BPF_X) {
-                               status = emit_moddiv(compiler, pc, BJ_XREG, 0);
+                               status = emit_moddiv(compiler, pc);
                                if (status != SLJIT_SUCCESS)
                                        goto fail;
                        } else if (pc->k != 0) {
-                               /* XXX: We can do better here for MOD */
-                               if ((pc->k & (pc->k - 1)) || op == BPF_MOD) {
-                                       status = emit_moddiv(compiler, pc,
-                                           SLJIT_IMM, (uint32_t)pc->k);
+                               if (pc->k & (pc->k - 1)) {
+                                       status = emit_moddiv(compiler, pc);
                                } else {
-                                   status = emit_pow2_division(compiler,
-                                       (uint32_t)pc->k);
+                                       status = emit_pow2_moddiv(compiler, pc);
                                }
                                if (status != SLJIT_SUCCESS)
                                        goto fail;