* [PATCH] [RISC-V] optimize Zicond conditional select cases.
@ 2024-04-15 6:33 Fei Gao
2024-04-15 12:58 ` Kito Cheng
0 siblings, 1 reply; 6+ messages in thread
From: Fei Gao @ 2024-04-15 6:33 UTC (permalink / raw)
To: gcc-patches; +Cc: kito.cheng, palmer, jeffreyalaw, Fei Gao
When one of the two input operands is 0, ADD and IOR are functionally
equivalent.
ADD is slightly preferred over IOR because ADD has a higher likelihood
of being implemented as a compressed instruction when compared to IOR.
C.ADD uses the CR format with any of the 32 RVI registers availble,
while C.OR uses the CA format with limit to just 8 of them.
Conditional select, if zero case:
rd = (rc == 0) ? rs1 : rs2
before patch:
czero.nez rd, rs1, rc
czero.eqz rtmp, rs2, rc
or rd, rd, rtmp
after patch:
czero.eqz rd, rs1, rc
czero.nez rtmp, rs2, rc
add rd, rd, rtmp
Same trick applies for the conditional select, if non-zero case:
rd = (rc != 0) ? rs1 : rs2
riscv-gnu-toolchain regression tests have been passed with no new failure.
---
gcc/config/riscv/riscv.cc | 2 +-
.../gcc.target/riscv/zicond-prefer-add-to-or.c | 16 ++++++++++++++++
2 files changed, 17 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index e5f00806bb9..93c736549c9 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -4709,7 +4709,7 @@ riscv_expand_conditional_move (rtx dest, rtx op, rtx cons, rtx alt)
gen_rtx_IF_THEN_ELSE (mode, cond1,
CONST0_RTX (mode),
alt)));
- riscv_emit_binary (IOR, dest, reg1, reg2);
+ riscv_emit_binary (PLUS, dest, reg1, reg2);
return true;
}
}
diff --git a/gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c b/gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
new file mode 100644
index 00000000000..f3f7beb0b5e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
@@ -0,0 +1,16 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zicond -mabi=lp64d -mbranch-cost=4" { target { rv64 } } } */
+/* { dg-options "-march=rv32gc_zicond -mabi=ilp32f -mbranch-cost=4" { target { rv32 } } } */
+/* { dg-skip-if "" { *-*-* } {"-O0" "-Og" "-Os" "-Oz"} } */
+
+long cond_select_if_zero(long a, long b, long c) {
+ return a == 0 ? c : b;
+}
+
+long cond_select_if_non_zero(long a, long b, long c) {
+ return a != 0 ? c : b;
+}
+
+/* { dg-final { scan-assembler-times {add\t} 2 } } */
+/* { dg-final { scan-assembler-not {or\t} } } */
+
--
2.17.1
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] [RISC-V] optimize Zicond conditional select cases.
2024-04-15 6:33 [PATCH] [RISC-V] optimize Zicond conditional select cases Fei Gao
@ 2024-04-15 12:58 ` Kito Cheng
2024-04-15 13:04 ` Jeff Law
0 siblings, 1 reply; 6+ messages in thread
From: Kito Cheng @ 2024-04-15 12:58 UTC (permalink / raw)
To: Fei Gao; +Cc: GCC Patches, Palmer Dabbelt, Jeff Law
[-- Attachment #1: Type: text/plain, Size: 2812 bytes --]
It's simple enough, so LGTM for trunk :)
Fei Gao <gaofei@eswincomputing.com> 於 2024年4月15日 週一 14:38 寫道:
> When one of the two input operands is 0, ADD and IOR are functionally
> equivalent.
> ADD is slightly preferred over IOR because ADD has a higher likelihood
> of being implemented as a compressed instruction when compared to IOR.
> C.ADD uses the CR format with any of the 32 RVI registers availble,
> while C.OR uses the CA format with limit to just 8 of them.
>
> Conditional select, if zero case:
> rd = (rc == 0) ? rs1 : rs2
>
> before patch:
>
> czero.nez rd, rs1, rc
> czero.eqz rtmp, rs2, rc
> or rd, rd, rtmp
>
> after patch:
>
> czero.eqz rd, rs1, rc
> czero.nez rtmp, rs2, rc
> add rd, rd, rtmp
>
> Same trick applies for the conditional select, if non-zero case:
> rd = (rc != 0) ? rs1 : rs2
>
> riscv-gnu-toolchain regression tests have been passed with no new failure.
> ---
> gcc/config/riscv/riscv.cc | 2 +-
> .../gcc.target/riscv/zicond-prefer-add-to-or.c | 16 ++++++++++++++++
> 2 files changed, 17 insertions(+), 1 deletion(-)
> create mode 100644
> gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
>
> diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> index e5f00806bb9..93c736549c9 100644
> --- a/gcc/config/riscv/riscv.cc
> +++ b/gcc/config/riscv/riscv.cc
> @@ -4709,7 +4709,7 @@ riscv_expand_conditional_move (rtx dest, rtx op, rtx
> cons, rtx alt)
> gen_rtx_IF_THEN_ELSE (mode, cond1,
> CONST0_RTX (mode),
> alt)));
> - riscv_emit_binary (IOR, dest, reg1, reg2);
> + riscv_emit_binary (PLUS, dest, reg1, reg2);
> return true;
> }
> }
> diff --git a/gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
> b/gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
> new file mode 100644
> index 00000000000..f3f7beb0b5e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/riscv/zicond-prefer-add-to-or.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-march=rv64gc_zicond -mabi=lp64d -mbranch-cost=4" {
> target { rv64 } } } */
> +/* { dg-options "-march=rv32gc_zicond -mabi=ilp32f -mbranch-cost=4" {
> target { rv32 } } } */
> +/* { dg-skip-if "" { *-*-* } {"-O0" "-Og" "-Os" "-Oz"} } */
> +
> +long cond_select_if_zero(long a, long b, long c) {
> + return a == 0 ? c : b;
> +}
> +
> +long cond_select_if_non_zero(long a, long b, long c) {
> + return a != 0 ? c : b;
> +}
> +
> +/* { dg-final { scan-assembler-times {add\t} 2 } } */
> +/* { dg-final { scan-assembler-not {or\t} } } */
> +
> --
> 2.17.1
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] [RISC-V] optimize Zicond conditional select cases.
2024-04-15 12:58 ` Kito Cheng
@ 2024-04-15 13:04 ` Jeff Law
2024-04-16 1:27 ` Fei Gao
0 siblings, 1 reply; 6+ messages in thread
From: Jeff Law @ 2024-04-15 13:04 UTC (permalink / raw)
To: Kito Cheng, Fei Gao; +Cc: GCC Patches, Palmer Dabbelt
On 4/15/24 6:58 AM, Kito Cheng wrote:
> It's simple enough, so LGTM for trunk :)
We're already doing this internally. I just hadn't submitted it due to
being deep into stage4.
Jeff
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Re: [PATCH] [RISC-V] optimize Zicond conditional select cases.
2024-04-15 13:04 ` Jeff Law
@ 2024-04-16 1:27 ` Fei Gao
2024-04-16 2:05 ` Jeff Law
0 siblings, 1 reply; 6+ messages in thread
From: Fei Gao @ 2024-04-16 1:27 UTC (permalink / raw)
To: jeffreyalaw, Kito Cheng; +Cc: gcc-patches, Palmer Dabbelt
On 2024-04-15 21:04 Jeff Law <jeffreyalaw@gmail.com> wrote:
>
>
>
>On 4/15/24 6:58 AM, Kito Cheng wrote:
>> It's simple enough, so LGTM for trunk :)
>We're already doing this internally. I just hadn't submitted it due to
>being deep into stage4.
>
>Jeff
Hi Jeff
Would you like me to commit it now or leave it to you with your bunch of optimizations in Zicond?
BR
Fei
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] [RISC-V] optimize Zicond conditional select cases.
2024-04-16 1:27 ` Fei Gao
@ 2024-04-16 2:05 ` Jeff Law
2024-04-16 5:50 ` Fei Gao
0 siblings, 1 reply; 6+ messages in thread
From: Jeff Law @ 2024-04-16 2:05 UTC (permalink / raw)
To: Fei Gao, Kito Cheng; +Cc: gcc-patches, Palmer Dabbelt
On 4/15/24 7:27 PM, Fei Gao wrote:
> On 2024-04-15 21:04 Jeff Law <jeffreyalaw@gmail.com> wrote:
>>
>>
>>
>> On 4/15/24 6:58 AM, Kito Cheng wrote:
>>> It's simple enough, so LGTM for trunk :)
>> We're already doing this internally. I just hadn't submitted it due to
>> being deep into stage4.
>>
>> Jeff
>
> Hi Jeff
>
> Would you like me to commit it now or leave it to you with your bunch of optimizations in Zicond?
Go ahead and commit it. It's extremely low risk.
jeff
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] [RISC-V] optimize Zicond conditional select cases.
2024-04-16 2:05 ` Jeff Law
@ 2024-04-16 5:50 ` Fei Gao
0 siblings, 0 replies; 6+ messages in thread
From: Fei Gao @ 2024-04-16 5:50 UTC (permalink / raw)
To: jeffreyalaw, Kito Cheng; +Cc: gcc-patches, Palmer Dabbelt
Committed. Thanks Kito and Jeff for the reveiw.
BR
Fei
>
>
>On 4/15/24 7:27 PM, Fei Gao wrote:
>> On 2024-04-15 21:04 Jeff Law <jeffreyalaw@gmail.com> wrote:
>>>
>>>
>>>
>>> On 4/15/24 6:58 AM, Kito Cheng wrote:
>>>> It's simple enough, so LGTM for trunk :)
>>> We're already doing this internally. I just hadn't submitted it due to
>>> being deep into stage4.
>>>
>>> Jeff
>>
>> Hi Jeff
>>
>> Would you like me to commit it now or leave it to you with your bunch of optimizations in Zicond?
>Go ahead and commit it. It's extremely low risk.
>
>jeff
^ permalink raw reply [flat|nested] 6+ messages in thread
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2024-04-15 6:33 [PATCH] [RISC-V] optimize Zicond conditional select cases Fei Gao
2024-04-15 12:58 ` Kito Cheng
2024-04-15 13:04 ` Jeff Law
2024-04-16 1:27 ` Fei Gao
2024-04-16 2:05 ` Jeff Law
2024-04-16 5:50 ` Fei Gao
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