Re: [PATCH v2 09/12] target/riscv/cpu.h: use 'vlenb' in vext_get

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Re: [PATCH v2 09/12] target/riscv/cpu.h: use 'vlenb' in vext_get_vlmax()

From:	Richard Henderson
Subject:	Re: [PATCH v2 09/12] target/riscv/cpu.h: use 'vlenb' in vext_get_vlmax()
Date:	Tue, 16 Jan 2024 10:14:39 +1100
User-agent:	Mozilla Thunderbird

On 1/16/24 09:25, Daniel Henrique Barboza wrote:

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
  target/riscv/cpu.h | 6 +++++-
  1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 11df226a00..7304e478c2 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -692,7 +692,11 @@ static inline uint32_t vext_get_vlmax(RISCVCPU *cpu, 
target_ulong vtype)
  {
      uint8_t sew = FIELD_EX64(vtype, VTYPE, VSEW);
      int8_t lmul = sextract32(FIELD_EX64(vtype, VTYPE, VLMUL), 0, 3);
-    return cpu->cfg.vlen >> (sew + 3 - lmul);
+    /*
+     * vlmax = vlen >> (sew + 3 - lmul). With vlenb,
+     * 3 less shifts: vlenb >> (sew + 3 - 3 - lmul)
+     */
+    return cpu->cfg.vlenb >> (sew - lmul);
  }


I take it back -- this doesn't work without the + 3:

  sew = 0
  lmul = 3

   vlenb >> (0 - 3)
 = vlenb >> -3

Need

  vlen = vlenb << 3
  vlmax = vlen >> (0 + 3 - 3)
        = vlen >> 0
        = vlen


r~

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Re: [PATCH v2 05/12] target/riscv/insn_trans/trans_rvv.c.inc: use 'vlenb', (continued)
- [PATCH v2 06/12] target/riscv/insn_trans/trans_rvvk.c.inc: use 'vlenb', Daniel Henrique Barboza, 2024/01/15
  - Re: [PATCH v2 06/12] target/riscv/insn_trans/trans_rvvk.c.inc: use 'vlenb', Richard Henderson, 2024/01/16
- [PATCH v2 07/12] target/riscv/vector_helper.c: use 'vlenb', Daniel Henrique Barboza, 2024/01/15
  - Re: [PATCH v2 07/12] target/riscv/vector_helper.c: use 'vlenb', Richard Henderson, 2024/01/15
- [PATCH v2 08/12] target/riscv/vector_helper.c: use vlenb in HELPER(vsetvl), Daniel Henrique Barboza, 2024/01/15
  - Re: [PATCH v2 08/12] target/riscv/vector_helper.c: use vlenb in HELPER(vsetvl), Richard Henderson, 2024/01/15
    - Re: [PATCH v2 08/12] target/riscv/vector_helper.c: use vlenb in HELPER(vsetvl), Daniel Henrique Barboza, 2024/01/16
- [PATCH v2 09/12] target/riscv/cpu.h: use 'vlenb' in vext_get_vlmax(), Daniel Henrique Barboza, 2024/01/15
  - Re: [PATCH v2 09/12] target/riscv/cpu.h: use 'vlenb' in vext_get_vlmax(), Richard Henderson, 2024/01/15
  - Re: [PATCH v2 09/12] target/riscv/cpu.h: use 'vlenb' in vext_get_vlmax(), Richard Henderson <=
    - Re: [PATCH v2 09/12] target/riscv/cpu.h: use 'vlenb' in vext_get_vlmax(), Daniel Henrique Barboza, 2024/01/16
- [PATCH v2 10/12] target/riscv/insn_trans/trans_rvv.c.inc: use 'vlenb' in MAXSZ(), Daniel Henrique Barboza, 2024/01/15
  - Re: [PATCH v2 10/12] target/riscv/insn_trans/trans_rvv.c.inc: use 'vlenb' in MAXSZ(), Richard Henderson, 2024/01/15
- [PATCH v2 11/12] trans_rvv.c.inc: use 'vlenb' to calc vlmax in trans_vrgather_v*(), Daniel Henrique Barboza, 2024/01/15
- [PATCH v2 12/12] target/riscv/cpu.c: remove cpu->cfg.vlen, Daniel Henrique Barboza, 2024/01/15
  - Re: [PATCH v2 12/12] target/riscv/cpu.c: remove cpu->cfg.vlen, Richard Henderson, 2024/01/15

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