Hi,
Jiufu Guo via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> Hi!
>
> Segher Boessenkool <seg...@kernel.crashing.org> writes:
>
>> Hi!
>>
>> On Fri, Jun 16, 2023 at 04:34:12PM +0800, Jiufu Guo wrote:
>>> +/* Check if value C can be built by 2 instructions: one is 'li', another is
>>> + rotldi.
>>> +
>>> + If so, *SHIFT is set to the shift operand of rotldi(rldicl), and *MASK
>>> + is set to -1, and return true. Return false otherwise. */
>>
>> Don't say "is set to -1", the point of having this is so you say "is set
>> to the "li" value". Just like you describe what SHIFT is for.
> Yes, thanks!
>>
>>> +static bool
>>> +can_be_built_by_li_and_rotldi (HOST_WIDE_INT c, int *shift,
>>> + HOST_WIDE_INT *mask)
>>> +{
>>> + int n;
>>
>> Put shis later, like:
> Thanks!
>>
>>> + /* Check if C can be rotated to a positive or negative value
>>> + which 'li' instruction is able to load. */
>> int n;
>>> + if (can_be_rotated_to_lowbits (c, 15, &n)
>>> + || can_be_rotated_to_lowbits (~c, 15, &n))
>>> + {
>>> + *mask = HOST_WIDE_INT_M1;
>>> + *shift = HOST_BITS_PER_WIDE_INT - n;
>>> + return true;
>>> + }
>>
>> It is tricky to see ~c will always work, since what is really done is -c
>> instead. Can you just use that here?
>
> Some explanation:
> A negative value of 'li' is:
> 0b11..11xxx there are 49 leading '1's, and the other 15 tailing bits can
> be 0 or 1. With the '~' operation, there are 49 '0's.
> After the value is rotated, there are still 49 '1's. (xxx may also be
> at head/tail.)
> For the rotated value, with the '~' operation, there are still 49 '0's.
>
> So, for a value, if there are 49 successive '1's (may cross head/tail).
> It should be able to rotate to low 15 bits after the '~' operation.
>
> It would not be enough if using the '-' operation, since '-x=~x+1' in
> the bit aspect. As the below case 'li_rotldi_3': 0xffff8531ffffffffLL
> (rotate left 0x8531 32bit).
> The '~c' is 0x7ace00000000, this can be rotated from 0x7ace. (~0x8531).
> But '-c' is 0x7ace00000001. this value is not good.
>
>>
>>> @@ -10266,15 +10291,14 @@ static void
>>> rs6000_emit_set_long_const (rtx dest, HOST_WIDE_INT c)
>>> {
>>> rtx temp;
>>> + int shift;
>>> + HOST_WIDE_INT mask;
>>> HOST_WIDE_INT ud1, ud2, ud3, ud4;
>>>
>>> ud1 = c & 0xffff;
>>> - c = c >> 16;
>>> - ud2 = c & 0xffff;
>>> - c = c >> 16;
>>> - ud3 = c & 0xffff;
>>> - c = c >> 16;
>>> - ud4 = c & 0xffff;
>>> + ud2 = (c >> 16) & 0xffff;
>>> + ud3 = (c >> 32) & 0xffff;
>>> + ud4 = (c >> 48) & 0xffff;
>>>
>>> if ((ud4 == 0xffff && ud3 == 0xffff && ud2 == 0xffff && (ud1 & 0x8000))
>>> || (ud4 == 0 && ud3 == 0 && ud2 == 0 && ! (ud1 & 0x8000)))
>>> @@ -10305,6 +10329,17 @@ rs6000_emit_set_long_const (rtx dest,
>>> HOST_WIDE_INT c)
>>> emit_move_insn (dest, gen_rtx_XOR (DImode, temp,
>>> GEN_INT ((ud2 ^ 0xffff) << 16)));
>>> }
>>> + else if (can_be_built_by_li_and_rotldi (c, &shift, &mask))
>>> + {
>>> + temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode);
>>> + unsigned HOST_WIDE_INT imm = (c | ~mask);
>>> + imm = (imm >> shift) | (imm << (HOST_BITS_PER_WIDE_INT - shift));
>>> +
>>> + emit_move_insn (temp, GEN_INT (imm));
>>> + if (shift != 0)
>>> + temp = gen_rtx_ROTATE (DImode, temp, GEN_INT (shift));
>>> + emit_move_insn (dest, temp);
>>> + }
>>
>> If you would rewrite so it isn't such a run-on thing with "else if",
>> instead using early outs, or even some factoring, you could declare the
>> variable used only in a tiny scope in that tiny scope instead.
>
> Yes! Early returning is better for a lot of cases. I would like
> to have a refactor patch.
>
>>
>>> --- /dev/null
>>> +++ b/gcc/testsuite/gcc.target/powerpc/const-build.c
>>> @@ -0,0 +1,54 @@
>>> +/* { dg-do run } */
>>> +/* { dg-options "-O2 -save-temps" } */
>>> +/* { dg-require-effective-target has_arch_ppc64 } */
>>
>> Please put a tiny comment here saying what this test is *for*? The file
>> name is a bit of hint already, but you can indicate much more in one or
>> two lines :-)
>
> Oh, yes, thanks for point out this!
>
>>
>> With those adjustments, okay for trunk. Thanks!
>>
>> (If -c doesn't work, it needs more explanation).
The patch is updated, and attached below.
If ok, I would like to commit the patch accordingly.
BR,
Jeff (Jiufu Guo)
If a constant is possible to be rotated to/from a positive or negative
value from "li", then "li;rotldi" can be used to build the constant.
gcc/ChangeLog:
* config/rs6000/rs6000.cc (can_be_built_by_li_and_rotldi): New function.
(rs6000_emit_set_long_const): Call can_be_built_by_li_and_rotldi.
gcc/testsuite/ChangeLog:
* gcc.target/powerpc/const-build.c: New test.
---
gcc/config/rs6000/rs6000.cc | 47 +++++++++++++--
.../gcc.target/powerpc/const-build.c | 57 +++++++++++++++++++
2 files changed, 98 insertions(+), 6 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/powerpc/const-build.c
diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index 42f49e4a56b..acc332acc05 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -10258,6 +10258,31 @@ rs6000_emit_set_const (rtx dest, rtx source)
return true;
}
+/* Check if value C can be built by 2 instructions: one is 'li', another is
+ rotldi.
+
+ If so, *SHIFT is set to the shift operand of rotldi(rldicl), and *MASK
+ is set to the mask operand of rotldi(rldicl), and return true.
+ Return false otherwise. */
+
+static bool
+can_be_built_by_li_and_rotldi (HOST_WIDE_INT c, int *shift,
+ HOST_WIDE_INT *mask)
+{
+ /* If C or ~C contains at least 49 successive zeros, then C can be rotated
+ to/from a positive or negative value that 'li' is able to load. */
+ int n;
+ if (can_be_rotated_to_lowbits (c, 15, &n)
+ || can_be_rotated_to_lowbits (~c, 15, &n))
+ {
+ *mask = HOST_WIDE_INT_M1;
+ *shift = HOST_BITS_PER_WIDE_INT - n;
+ return true;
+ }
+
+ return false;
+}
+
/* Subroutine of rs6000_emit_set_const, handling PowerPC64 DImode.
Output insns to set DEST equal to the constant C as a series of
lis, ori and shl instructions. */
@@ -10266,15 +10291,14 @@ static void
rs6000_emit_set_long_const (rtx dest, HOST_WIDE_INT c)
{
rtx temp;
+ int shift;
+ HOST_WIDE_INT mask;
HOST_WIDE_INT ud1, ud2, ud3, ud4;
ud1 = c & 0xffff;
- c = c >> 16;
- ud2 = c & 0xffff;
- c = c >> 16;
- ud3 = c & 0xffff;
- c = c >> 16;
- ud4 = c & 0xffff;
+ ud2 = (c >> 16) & 0xffff;
+ ud3 = (c >> 32) & 0xffff;
+ ud4 = (c >> 48) & 0xffff;
if ((ud4 == 0xffff && ud3 == 0xffff && ud2 == 0xffff && (ud1 & 0x8000))
|| (ud4 == 0 && ud3 == 0 && ud2 == 0 && ! (ud1 & 0x8000)))
@@ -10305,6 +10329,17 @@ rs6000_emit_set_long_const (rtx dest, HOST_WIDE_INT c)
emit_move_insn (dest, gen_rtx_XOR (DImode, temp,
GEN_INT ((ud2 ^ 0xffff) << 16)));
}
+ else if (can_be_built_by_li_and_rotldi (c, &shift, &mask))
+ {
+ temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode);
+ unsigned HOST_WIDE_INT imm = (c | ~mask);
+ imm = (imm >> shift) | (imm << (HOST_BITS_PER_WIDE_INT - shift));
+
+ emit_move_insn (temp, GEN_INT (imm));
+ if (shift != 0)
+ temp = gen_rtx_ROTATE (DImode, temp, GEN_INT (shift));
+ emit_move_insn (dest, temp);
+ }
else if (ud3 == 0 && ud4 == 0)
{
temp = !can_create_pseudo_p () ? dest : gen_reg_rtx (DImode);
diff --git a/gcc/testsuite/gcc.target/powerpc/const-build.c
b/gcc/testsuite/gcc.target/powerpc/const-build.c
new file mode 100644
index 00000000000..69b37e2bb53
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/const-build.c
@@ -0,0 +1,57 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -save-temps" } */
+/* { dg-require-effective-target has_arch_ppc64 } */
+
+/* Verify that two instructions are sucessfully used to build constants.
+ One insn is li or lis, another is rotate: rldicl, rldicr or rldic. */
+
+#define NOIPA __attribute__ ((noipa))
+
+struct fun
+{
+ long long (*f) (void);
+ long long val;
+};
+
+long long NOIPA
+li_rotldi_1 (void)
+{
+ return 0x7531000000000LL;
+}
+
+long long NOIPA
+li_rotldi_2 (void)
+{
+ return 0x2100000000000064LL;
+}
+
+long long NOIPA
+li_rotldi_3 (void)
+{
+ return 0xffff8531ffffffffLL;
+}
+
+long long NOIPA
+li_rotldi_4 (void)
+{
+ return 0x21ffffffffffff94LL;
+}
+
+struct fun arr[] = {
+ {li_rotldi_1, 0x7531000000000LL},
+ {li_rotldi_2, 0x2100000000000064LL},
+ {li_rotldi_3, 0xffff8531ffffffffLL},
+ {li_rotldi_4, 0x21ffffffffffff94LL},
+};
+
+/* { dg-final { scan-assembler-times {\mrotldi\M} 4 } } */
+
+int
+main ()
+{
+ for (int i = 0; i < sizeof (arr) / sizeof (arr[0]); i++)
+ if ((*arr[i].f) () != arr[i].val)
+ __builtin_abort ();
+
+ return 0;
+}
--
2.39.3
>
> Sure, some words as above.
>
> BR,
> Jeff (Jiufu Guo)
>
>>
>>
>> Segher
