* [PATCH] RISC-V: bitmanip: use bexti for "(a & (1 << BIT_NO)) ? 0 : -1"
@ 2022-11-08 19:55 Philipp Tomsich
2022-11-17 14:43 ` Jeff Law
0 siblings, 1 reply; 3+ messages in thread
From: Philipp Tomsich @ 2022-11-08 19:55 UTC (permalink / raw)
To: gcc-patches
Cc: Kito Cheng, Christoph Muellner, Vineet Gupta, Jeff Law,
Palmer Dabbelt, Philipp Tomsich
Consider creating a polarity-reversed mask from a set-bit (i.e., if
the bit is set, produce all-ones; otherwise: all-zeros). Using Zbb,
this can be expressed as bexti, followed by an addi of minus-one. To
enable the combiner to discover this opportunity, we need to split the
canonical expression for "(a & (1 << BIT_NO)) ? 0 : -1" into a form
combinable into bexti.
Consider the function:
long f(long a)
{
return (a & (1 << BIT_NO)) ? 0 : -1;
}
This produces the following sequence prior to this change:
andi a0,a0,16
seqz a0,a0
neg a0,a0
ret
Following this change, it results in:
bexti a0,a0,4
addi a0,a0,-1
ret
gcc/ChangeLog:
* config/riscv/bitmanip.md: Add a splitter to generate
polarity-reversed masks from a set bit using bexti + addi.
gcc/testsuite/ChangeLog:
* gcc.target/riscv/zbs-bexti.c: New test.
---
gcc/config/riscv/bitmanip.md | 13 +++++++++++++
gcc/testsuite/gcc.target/riscv/zbs-bexti.c | 14 ++++++++++++++
2 files changed, 27 insertions(+)
create mode 100644 gcc/testsuite/gcc.target/riscv/zbs-bexti.c
diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
index d26f3567182..30dabdf8ddc 100644
--- a/gcc/config/riscv/bitmanip.md
+++ b/gcc/config/riscv/bitmanip.md
@@ -394,3 +394,16 @@
"TARGET_ZBS && UINTVAL (operands[2]) < GET_MODE_BITSIZE (<MODE>mode)"
"bexti\t%0,%1,%2"
[(set_attr "type" "bitmanip")])
+
+;; We can create a polarity-reversed mask (i.e. bit N -> { set = 0, clear = -1 })
+;; using a bext(i) followed by an addi instruction.
+;; This splits the canonical representation of "(a & (1 << BIT_NO)) ? 0 : -1".
+(define_split
+ [(set (match_operand:GPR 0 "register_operand")
+ (neg:GPR (eq:GPR (zero_extract:GPR (match_operand:GPR 1 "register_operand")
+ (const_int 1)
+ (match_operand 2))
+ (const_int 0))))]
+ "TARGET_ZBS"
+ [(set (match_dup 0) (zero_extract:GPR (match_dup 1) (const_int 1) (match_dup 2)))
+ (set (match_dup 0) (plus:GPR (match_dup 0) (const_int -1)))])
diff --git a/gcc/testsuite/gcc.target/riscv/zbs-bexti.c b/gcc/testsuite/gcc.target/riscv/zbs-bexti.c
new file mode 100644
index 00000000000..99e3b58309c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zbs-bexti.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zbs -mabi=lp64 -O2" } */
+
+/* bexti */
+#define BIT_NO 4
+
+long
+foo0 (long a)
+{
+ return (a & (1 << BIT_NO)) ? 0 : -1;
+}
+
+/* { dg-final { scan-assembler "bexti" } } */
+/* { dg-final { scan-assembler "addi" } } */
--
2.34.1
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] RISC-V: bitmanip: use bexti for "(a & (1 << BIT_NO)) ? 0 : -1"
2022-11-08 19:55 [PATCH] RISC-V: bitmanip: use bexti for "(a & (1 << BIT_NO)) ? 0 : -1" Philipp Tomsich
@ 2022-11-17 14:43 ` Jeff Law
2022-11-17 15:25 ` Philipp Tomsich
0 siblings, 1 reply; 3+ messages in thread
From: Jeff Law @ 2022-11-17 14:43 UTC (permalink / raw)
To: Philipp Tomsich, gcc-patches
Cc: Kito Cheng, Christoph Muellner, Vineet Gupta, Jeff Law, Palmer Dabbelt
On 11/8/22 12:55, Philipp Tomsich wrote:
> Consider creating a polarity-reversed mask from a set-bit (i.e., if
> the bit is set, produce all-ones; otherwise: all-zeros). Using Zbb,
> this can be expressed as bexti, followed by an addi of minus-one. To
> enable the combiner to discover this opportunity, we need to split the
> canonical expression for "(a & (1 << BIT_NO)) ? 0 : -1" into a form
> combinable into bexti.
>
> Consider the function:
> long f(long a)
> {
> return (a & (1 << BIT_NO)) ? 0 : -1;
> }
> This produces the following sequence prior to this change:
> andi a0,a0,16
> seqz a0,a0
> neg a0,a0
> ret
> Following this change, it results in:
> bexti a0,a0,4
> addi a0,a0,-1
> ret
>
> gcc/ChangeLog:
>
> * config/riscv/bitmanip.md: Add a splitter to generate
> polarity-reversed masks from a set bit using bexti + addi.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/riscv/zbs-bexti.c: New test.
OK
Jeff
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] RISC-V: bitmanip: use bexti for "(a & (1 << BIT_NO)) ? 0 : -1"
2022-11-17 14:43 ` Jeff Law
@ 2022-11-17 15:25 ` Philipp Tomsich
0 siblings, 0 replies; 3+ messages in thread
From: Philipp Tomsich @ 2022-11-17 15:25 UTC (permalink / raw)
To: Jeff Law
Cc: gcc-patches, Kito Cheng, Christoph Muellner, Vineet Gupta,
Jeff Law, Palmer Dabbelt
Committed to master. Thanks!
Philipp.
On Thu, 17 Nov 2022 at 15:43, Jeff Law <jeffreyalaw@gmail.com> wrote:
>
>
> On 11/8/22 12:55, Philipp Tomsich wrote:
> > Consider creating a polarity-reversed mask from a set-bit (i.e., if
> > the bit is set, produce all-ones; otherwise: all-zeros). Using Zbb,
> > this can be expressed as bexti, followed by an addi of minus-one. To
> > enable the combiner to discover this opportunity, we need to split the
> > canonical expression for "(a & (1 << BIT_NO)) ? 0 : -1" into a form
> > combinable into bexti.
> >
> > Consider the function:
> > long f(long a)
> > {
> > return (a & (1 << BIT_NO)) ? 0 : -1;
> > }
> > This produces the following sequence prior to this change:
> > andi a0,a0,16
> > seqz a0,a0
> > neg a0,a0
> > ret
> > Following this change, it results in:
> > bexti a0,a0,4
> > addi a0,a0,-1
> > ret
> >
> > gcc/ChangeLog:
> >
> > * config/riscv/bitmanip.md: Add a splitter to generate
> > polarity-reversed masks from a set bit using bexti + addi.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.target/riscv/zbs-bexti.c: New test.
>
> OK
>
>
> Jeff
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-11-08 19:55 [PATCH] RISC-V: bitmanip: use bexti for "(a & (1 << BIT_NO)) ? 0 : -1" Philipp Tomsich
2022-11-17 14:43 ` Jeff Law
2022-11-17 15:25 ` Philipp Tomsich
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