* [PATCH] target/mips: Remove JR opcode unused arguments
@ 2021-07-30 22:55 Philippe Mathieu-Daudé
2021-07-31 19:54 ` Richard Henderson
2021-08-06 21:09 ` Philippe Mathieu-Daudé
0 siblings, 2 replies; 3+ messages in thread
From: Philippe Mathieu-Daudé @ 2021-07-30 22:55 UTC (permalink / raw)
To: qemu-devel
Cc: Aleksandar Rikalo, Richard Henderson, Aurelien Jarno,
Philippe Mathieu-Daudé
JR opcode (Jump Register) only takes 1 argument, $rs.
JALR (Jump And Link Register) takes 3: $rs, $rd and $hint.
Commit 6af0bf9c7c3 added their processing into decode_opc() as:
case 0x08 ... 0x09: /* Jumps */
gen_compute_branch(ctx, op1 | EXT_SPECIAL, rs, rd, sa);
having both opcodes handled in the same function: gen_compute_branch.
Per JR encoding, both $rd and $hint ('sa') are decoded as zero.
Later this code got extracted to decode_opc_special(),
commit 7a387fffce5 used definitions instead of magic values:
case OPC_JR ... OPC_JALR:
gen_compute_branch(ctx, op1, rs, rd, sa);
Finally commit 0aefa33318b moved OPC_JR out of decode_opc_special,
to a new 'decode_opc_special_legacy' function:
@@ -15851,6 +15851,9 @@ static void decode_opc_special_legacy(CPUMIPSState *env, DisasContext *ctx)
+ case OPC_JR:
+ gen_compute_branch(ctx, op1, 4, rs, rd, sa);
+ break;
@@ -15933,7 +15936,7 @@ static void decode_opc_special(CPUMIPSState *env, DisasContext *ctx)
- case OPC_JR ... OPC_JALR:
+ case OPC_JALR:
gen_compute_branch(ctx, op1, 4, rs, rd, sa);
break;
Since JR is now handled individually, it is pointless to decode
and pass it unused arguments. Replace them by simple zero value
to avoid confusion with this opcode.
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
target/mips/tcg/translate.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/target/mips/tcg/translate.c b/target/mips/tcg/translate.c
index 5b03545f099..bf71724f3f0 100644
--- a/target/mips/tcg/translate.c
+++ b/target/mips/tcg/translate.c
@@ -14203,7 +14203,7 @@ static void decode_opc_special_legacy(CPUMIPSState *env, DisasContext *ctx)
break;
#endif
case OPC_JR:
- gen_compute_branch(ctx, op1, 4, rs, rd, sa, 4);
+ gen_compute_branch(ctx, op1, 4, rs, 0, 0, 4);
break;
case OPC_SPIM:
#ifdef MIPS_STRICT_STANDARD
--
2.31.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] target/mips: Remove JR opcode unused arguments
2021-07-30 22:55 [PATCH] target/mips: Remove JR opcode unused arguments Philippe Mathieu-Daudé
@ 2021-07-31 19:54 ` Richard Henderson
2021-08-06 21:09 ` Philippe Mathieu-Daudé
1 sibling, 0 replies; 3+ messages in thread
From: Richard Henderson @ 2021-07-31 19:54 UTC (permalink / raw)
To: Philippe Mathieu-Daudé, qemu-devel; +Cc: Aleksandar Rikalo, Aurelien Jarno
On 7/30/21 12:55 PM, Philippe Mathieu-Daudé wrote:
> case OPC_JR:
> - gen_compute_branch(ctx, op1, 4, rs, rd, sa, 4);
> + gen_compute_branch(ctx, op1, 4, rs, 0, 0, 4);
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
r~
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] target/mips: Remove JR opcode unused arguments
2021-07-30 22:55 [PATCH] target/mips: Remove JR opcode unused arguments Philippe Mathieu-Daudé
2021-07-31 19:54 ` Richard Henderson
@ 2021-08-06 21:09 ` Philippe Mathieu-Daudé
1 sibling, 0 replies; 3+ messages in thread
From: Philippe Mathieu-Daudé @ 2021-08-06 21:09 UTC (permalink / raw)
To: qemu-devel; +Cc: Aleksandar Rikalo, Richard Henderson, Aurelien Jarno
On 7/31/21 12:55 AM, Philippe Mathieu-Daudé wrote:
> JR opcode (Jump Register) only takes 1 argument, $rs.
> JALR (Jump And Link Register) takes 3: $rs, $rd and $hint.
>
> Commit 6af0bf9c7c3 added their processing into decode_opc() as:
>
> case 0x08 ... 0x09: /* Jumps */
> gen_compute_branch(ctx, op1 | EXT_SPECIAL, rs, rd, sa);
>
> having both opcodes handled in the same function: gen_compute_branch.
>
> Per JR encoding, both $rd and $hint ('sa') are decoded as zero.
>
> Later this code got extracted to decode_opc_special(),
> commit 7a387fffce5 used definitions instead of magic values:
>
> case OPC_JR ... OPC_JALR:
> gen_compute_branch(ctx, op1, rs, rd, sa);
>
> Finally commit 0aefa33318b moved OPC_JR out of decode_opc_special,
> to a new 'decode_opc_special_legacy' function:
>
> @@ -15851,6 +15851,9 @@ static void decode_opc_special_legacy(CPUMIPSState *env, DisasContext *ctx)
> + case OPC_JR:
> + gen_compute_branch(ctx, op1, 4, rs, rd, sa);
> + break;
>
> @@ -15933,7 +15936,7 @@ static void decode_opc_special(CPUMIPSState *env, DisasContext *ctx)
> - case OPC_JR ... OPC_JALR:
> + case OPC_JALR:
> gen_compute_branch(ctx, op1, 4, rs, rd, sa);
> break;
>
> Since JR is now handled individually, it is pointless to decode
> and pass it unused arguments. Replace them by simple zero value
> to avoid confusion with this opcode.
>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
> target/mips/tcg/translate.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
Thanks, applied to mips-next.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-07-30 22:55 [PATCH] target/mips: Remove JR opcode unused arguments Philippe Mathieu-Daudé
2021-07-31 19:54 ` Richard Henderson
2021-08-06 21:09 ` Philippe Mathieu-Daudé
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