[v1] RISC-V: bitmanip: improve constant-loading for (1ULL << 31) in DImode
Commit Message
The SINGLE_BIT_MASK_OPERAND() is overly restrictive, triggering for
bits above 31 only (to side-step any issues with the negative SImode
value 0x80000000). This moves the special handling of this SImode
value (i.e. the check for -2147483648) to riscv.cc and relaxes the
SINGLE_BIT_MASK_OPERAND() test.
This changes the code-generation for loading (1ULL << 31) from:
li a0,1
slli a0,a0,31
to:
bseti a0,zero,31
gcc/ChangeLog:
* config/riscv/riscv.cc (riscv_build_integer_1): Rewrite value as
-2147483648 for the single-bit case, when operating on 0x80000000
in SImode.
* gcc/config/riscv/riscv.h (SINGLE_BIT_MASK_OPERAND): Allow for
any single-bit value, moving the special case for 0x80000000 to
riscv_build_integer_1 (in riscv.c).
Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
---
gcc/config/riscv/riscv.cc | 9 +++++++++
gcc/config/riscv/riscv.h | 11 ++++-------
2 files changed, 13 insertions(+), 7 deletions(-)
Comments
On Tue, May 24, 2022 at 3:57 PM Philipp Tomsich
<philipp.tomsich@vrull.eu> wrote:
>
> The SINGLE_BIT_MASK_OPERAND() is overly restrictive, triggering for
> bits above 31 only (to side-step any issues with the negative SImode
> value 0x80000000). This moves the special handling of this SImode
> value (i.e. the check for -2147483648) to riscv.cc and relaxes the
> SINGLE_BIT_MASK_OPERAND() test.
>
> This changes the code-generation for loading (1ULL << 31) from:
> li a0,1
> slli a0,a0,31
> to:
> bseti a0,zero,31
>
> gcc/ChangeLog:
>
> * config/riscv/riscv.cc (riscv_build_integer_1): Rewrite value as
> -2147483648 for the single-bit case, when operating on 0x80000000
> in SImode.
> * gcc/config/riscv/riscv.h (SINGLE_BIT_MASK_OPERAND): Allow for
> any single-bit value, moving the special case for 0x80000000 to
> riscv_build_integer_1 (in riscv.c).
>
> Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
>
> ---
>
> gcc/config/riscv/riscv.cc | 9 +++++++++
> gcc/config/riscv/riscv.h | 11 ++++-------
> 2 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> index f83dc796d88..fe8196f5c80 100644
> --- a/gcc/config/riscv/riscv.cc
> +++ b/gcc/config/riscv/riscv.cc
> @@ -420,6 +420,15 @@ riscv_build_integer_1 (struct riscv_integer_op codes[RISCV_MAX_INTEGER_OPS],
> /* Simply BSETI. */
> codes[0].code = UNKNOWN;
> codes[0].value = value;
> +
> + /* RISC-V sign-extends all 32bit values that life in a 32bit
> + register. To avoid paradoxes, we thus need to use the
> + sign-extended (negative) representation for the value, if we
> + want to build 0x80000000 in SImode. This will then expand
> + to an ADDI/LI instruction. */
> + if (mode == SImode && value == 0x80000000)
> + codes[0].value = -2147483648;
Instead it is better to use HOST_WIDE_INT_M1U<<31 here instead of the
number -2147483648 since I have no idea what that is.
Like for 0x80000000 to be HOST_WIDE_INT_1U<<31 ?
Thanks,
Andrew Pinski
> +
> return 1;
> }
>
> diff --git a/gcc/config/riscv/riscv.h b/gcc/config/riscv/riscv.h
> index 5083a1c24b0..6f7f4d3fbdc 100644
> --- a/gcc/config/riscv/riscv.h
> +++ b/gcc/config/riscv/riscv.h
> @@ -528,13 +528,10 @@ enum reg_class
> (((VALUE) | ((1UL<<31) - IMM_REACH)) == ((1UL<<31) - IMM_REACH) \
> || ((VALUE) | ((1UL<<31) - IMM_REACH)) + IMM_REACH == 0)
>
> -/* If this is a single bit mask, then we can load it with bseti. But this
> - is not useful for any of the low 31 bits because we can use addi or lui
> - to load them. It is wrong for loading SImode 0x80000000 on rv64 because it
> - needs to be sign-extended. So we restrict this to the upper 32-bits
> - only. */
> -#define SINGLE_BIT_MASK_OPERAND(VALUE) \
> - (pow2p_hwi (VALUE) && (ctz_hwi (VALUE) >= 32))
> +/* If this is a single bit mask, then we can load it with bseti. Special
> + handling of SImode 0x80000000 on RV64 is done in riscv_build_integer_1. */
> +#define SINGLE_BIT_MASK_OPERAND(VALUE) \
> + (pow2p_hwi (VALUE))
>
> /* Stack layout; function entry, exit and calling. */
>
> --
> 2.34.1
>
@@ -420,6 +420,15 @@ riscv_build_integer_1 (struct riscv_integer_op codes[RISCV_MAX_INTEGER_OPS],
/* Simply BSETI. */
codes[0].code = UNKNOWN;
codes[0].value = value;
+
+ /* RISC-V sign-extends all 32bit values that life in a 32bit
+ register. To avoid paradoxes, we thus need to use the
+ sign-extended (negative) representation for the value, if we
+ want to build 0x80000000 in SImode. This will then expand
+ to an ADDI/LI instruction. */
+ if (mode == SImode && value == 0x80000000)
+ codes[0].value = -2147483648;
+
return 1;
}
@@ -528,13 +528,10 @@ enum reg_class
(((VALUE) | ((1UL<<31) - IMM_REACH)) == ((1UL<<31) - IMM_REACH) \
|| ((VALUE) | ((1UL<<31) - IMM_REACH)) + IMM_REACH == 0)
-/* If this is a single bit mask, then we can load it with bseti. But this
- is not useful for any of the low 31 bits because we can use addi or lui
- to load them. It is wrong for loading SImode 0x80000000 on rv64 because it
- needs to be sign-extended. So we restrict this to the upper 32-bits
- only. */
-#define SINGLE_BIT_MASK_OPERAND(VALUE) \
- (pow2p_hwi (VALUE) && (ctz_hwi (VALUE) >= 32))
+/* If this is a single bit mask, then we can load it with bseti. Special
+ handling of SImode 0x80000000 on RV64 is done in riscv_build_integer_1. */
+#define SINGLE_BIT_MASK_OPERAND(VALUE) \
+ (pow2p_hwi (VALUE))
/* Stack layout; function entry, exit and calling. */