target/mips: Simplify Loongson MULTU.G opcode

[PATCH] target/mips: Simplify Loongson MULTU.G opcode

Philippe Mathieu-Daudé posted 1 patch 8 months ago

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git fetch https://github.com/patchew-project/qemu tags/patchew/20230831201140.85799-1-philmd@linaro.org

Maintainers: "Philippe Mathieu-Daudé" <philmd@linaro.org>, Aurelien Jarno <aurelien@aurel32.net>, Jiaxun Yang <jiaxun.yang@flygoat.com>, Aleksandar Rikalo <aleksandar.rikalo@syrmia.com>

target/mips/tcg/translate.c | 2 --
1 file changed, 2 deletions(-)

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[PATCH] target/mips: Simplify Loongson MULTU.G opcode

Posted by Philippe Mathieu-Daudé 8 months ago

Since MULTU opcodes don't record the most significant bits
of the infinite result, sign-extending the sources make no
difference in the result.

Once we remove the sign extension of source registers, MULT
and MULTU are identical (as are DMULT and DMULTU).

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 target/mips/tcg/translate.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/target/mips/tcg/translate.c b/target/mips/tcg/translate.c
index 9bb40f1849..e0a76b9432 100644
--- a/target/mips/tcg/translate.c
+++ b/target/mips/tcg/translate.c
@@ -3625,8 +3625,6 @@ static void gen_loongson_integer(DisasContext *ctx, uint32_t opc,
         break;
     case OPC_MULTU_G_2E:
     case OPC_MULTU_G_2F:
-        tcg_gen_ext32u_tl(t0, t0);
-        tcg_gen_ext32u_tl(t1, t1);
         tcg_gen_mul_tl(cpu_gpr[rd], t0, t1);
         tcg_gen_ext32s_tl(cpu_gpr[rd], cpu_gpr[rd]);
         break;
-- 
2.41.0

Re: [PATCH] target/mips: Simplify Loongson MULTU.G opcode

Posted by Richard Henderson 8 months ago

On 8/31/23 13:11, Philippe Mathieu-Daudé wrote:
> Since MULTU opcodes don't record the most significant bits
> of the infinite result, sign-extending the sources make no
> difference in the result.
> 
> Once we remove the sign extension of source registers, MULT
> and MULTU are identical (as are DMULT and DMULTU).
> 
> Suggested-by: Richard Henderson<richard.henderson@linaro.org>
> Signed-off-by: Philippe Mathieu-Daudé<philmd@linaro.org>
> ---
>   target/mips/tcg/translate.c | 2 --
>   1 file changed, 2 deletions(-)

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

r~