[ARC PATCH] Convert (signed<<31)>>31 to -(signed&1) without barrel shifter.

[ARC PATCH] Convert (signed<<31)>>31 to -(signed&1) without barrel shifter.

[Roger Sayle]

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This patch optimizes PR middle-end/101955 for the ARC backend.  On ARC
CPUs with a barrel shifter, using two shifts is (probably) optimal as:

        asl_s   r0,r0,31
        asr_s   r0,r0,31

but without a barrel shifter, GCC -O2 -mcpu=em currently generates:

        and     r2,r0,1
        ror     r2,r2
        add.f   0,r2,r2
        sbc     r0,r0,r0

with this patch, we now generate the smaller, faster and non-flags
clobbering:

        bmsk_s  r0,r0,0
        neg_s   r0,r0

Tested with a cross-compiler to arc-linux hosted on x86_64,
with no new (compile-only) regressions from make -k check.
Ok for mainline if this passes Claudiu's nightly testing?


2023-10-28  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        PR middle-end/101955
        * config/arc/arc.md (*extvsi_1_0): New define_insn_and_split
        to convert sign extract of the least significant bit into an
        AND $1 then a NEG when !TARGET_BARREL_SHIFTER.

gcc/testsuite/ChangeLog
        PR middle-end/101955
        * gcc.target/arc/pr101955.c: New test case.


Thanks again,
Roger
--


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diff --git a/gcc/config/arc/arc.md b/gcc/config/arc/arc.md
index ee43887..6471344 100644
--- a/gcc/config/arc/arc.md
+++ b/gcc/config/arc/arc.md
@@ -5873,6 +5873,20 @@ archs4x, archs4xd"
 		   (zero_extract:SI (match_dup 1) (match_dup 5) (match_dup 7)))])
    (match_dup 1)])
 
+;; Split sign-extension of single least significant bit as and x,$1;neg x
+(define_insn_and_split "*extvsi_1_0"
+  [(set (match_operand:SI 0 "register_operand" "=r")
+	(sign_extract:SI (match_operand:SI 1 "register_operand" "0")
+			 (const_int 1)
+			 (const_int 0)))]
+  "!TARGET_BARREL_SHIFTER"
+  "#"
+  "&& 1"
+  [(set (match_dup 0) (and:SI (match_dup 1) (const_int 1)))
+   (set (match_dup 0) (neg:SI (match_dup 0)))]
+  ""
+  [(set_attr "length" "8")])
+
 (define_insn_and_split "rotlsi3_cnt1"
   [(set (match_operand:SI 0 "dest_reg_operand"            "=r")
 	(rotate:SI (match_operand:SI 1 "register_operand" "r")
diff --git a/gcc/testsuite/gcc.target/arc/pr101955.c b/gcc/testsuite/gcc.target/arc/pr101955.c
new file mode 100644
index 0000000..74bca3c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arc/pr101955.c
@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -mcpu=em" } */
+
+int f(int a)
+{
+    return (a << 31) >> 31;
+}
+
+/* { dg-final { scan-assembler "msk_s\\s+r0,r0,0" } } */
+/* { dg-final { scan-assembler "neg_s\\s+r0,r0" } } */

Re: [ARC PATCH] Convert (signed<<31)>>31 to -(signed&1) without barrel shifter.

[Jeff Law]

On 10/28/23 10:47, Roger Sayle wrote:
> 
> This patch optimizes PR middle-end/101955 for the ARC backend.  On ARC
> CPUs with a barrel shifter, using two shifts is (probably) optimal as:
> 
>          asl_s   r0,r0,31
>          asr_s   r0,r0,31
> 
> but without a barrel shifter, GCC -O2 -mcpu=em currently generates:
> 
>          and     r2,r0,1
>          ror     r2,r2
>          add.f   0,r2,r2
>          sbc     r0,r0,r0
> 
> with this patch, we now generate the smaller, faster and non-flags
> clobbering:
> 
>          bmsk_s  r0,r0,0
>          neg_s   r0,r0
> 
> Tested with a cross-compiler to arc-linux hosted on x86_64,
> with no new (compile-only) regressions from make -k check.
> Ok for mainline if this passes Claudiu's nightly testing?
> 
> 
> 2023-10-28  Roger Sayle  <roger@nextmovesoftware.com>
> 
> gcc/ChangeLog
>          PR middle-end/101955
>          * config/arc/arc.md (*extvsi_1_0): New define_insn_and_split
>          to convert sign extract of the least significant bit into an
>          AND $1 then a NEG when !TARGET_BARREL_SHIFTER.
> 
> gcc/testsuite/ChangeLog
>          PR middle-end/101955
>          * gcc.target/arc/pr101955.c: New test case.
Good catch.  Looking to do something very similar on the H8 based on 
your work here.

One the H8 we can use bld to load a bit from an 8 bit register into the 
C flag.  Then we use subtract with carry to get an 8 bit 0/-1 which we 
can then sign extend to 16 or 32 bits.  That covers bit positions 0..15 
of an SImode input.

For bits 16..31 we can move the high half into the low half, the use the 
bld sequence.

For bit zero the and+neg is the same number of clocks and size as bld 
based sequence.  But it'll simulate faster, so it's special cased.


Jeff

Re: [ARC PATCH] Convert (signed<<31)>>31 to -(signed&1) without barrel shifter.

[Claudiu Zissulescu Ianculescu]

Hi Roger,

Do you want to say bmsk_s instead of msk_s here:
+/* { dg-final { scan-assembler "msk_s\\s+r0,r0,0" } } */

Anyhow, the patch looks good. Proceed with your commit.

Thank you,
Claudiu

On Mon, Oct 30, 2023 at 5:05 AM Jeff Law <jeffreyalaw@gmail.com> wrote:
>
>
>
> On 10/28/23 10:47, Roger Sayle wrote:
> >
> > This patch optimizes PR middle-end/101955 for the ARC backend.  On ARC
> > CPUs with a barrel shifter, using two shifts is (probably) optimal as:
> >
> >          asl_s   r0,r0,31
> >          asr_s   r0,r0,31
> >
> > but without a barrel shifter, GCC -O2 -mcpu=em currently generates:
> >
> >          and     r2,r0,1
> >          ror     r2,r2
> >          add.f   0,r2,r2
> >          sbc     r0,r0,r0
> >
> > with this patch, we now generate the smaller, faster and non-flags
> > clobbering:
> >
> >          bmsk_s  r0,r0,0
> >          neg_s   r0,r0
> >
> > Tested with a cross-compiler to arc-linux hosted on x86_64,
> > with no new (compile-only) regressions from make -k check.
> > Ok for mainline if this passes Claudiu's nightly testing?
> >
> >
> > 2023-10-28  Roger Sayle  <roger@nextmovesoftware.com>
> >
> > gcc/ChangeLog
> >          PR middle-end/101955
> >          * config/arc/arc.md (*extvsi_1_0): New define_insn_and_split
> >          to convert sign extract of the least significant bit into an
> >          AND $1 then a NEG when !TARGET_BARREL_SHIFTER.
> >
> > gcc/testsuite/ChangeLog
> >          PR middle-end/101955
> >          * gcc.target/arc/pr101955.c: New test case.
> Good catch.  Looking to do something very similar on the H8 based on
> your work here.
>
> One the H8 we can use bld to load a bit from an 8 bit register into the
> C flag.  Then we use subtract with carry to get an 8 bit 0/-1 which we
> can then sign extend to 16 or 32 bits.  That covers bit positions 0..15
> of an SImode input.
>
> For bits 16..31 we can move the high half into the low half, the use the
> bld sequence.
>
> For bit zero the and+neg is the same number of clocks and size as bld
> based sequence.  But it'll simulate faster, so it's special cased.
>
>
> Jeff
>