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Re: [Qemu-devel] [PATCH 04/26] tcg-aarch64: Use MOVN in tcg_out_movi
From: |
Claudio Fontana |
Subject: |
Re: [Qemu-devel] [PATCH 04/26] tcg-aarch64: Use MOVN in tcg_out_movi |
Date: |
Mon, 24 Mar 2014 15:06:11 +0100 |
User-agent: |
Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.0.1 |
On 15.03.2014 03:48, Richard Henderson wrote:
> When profitable, initialize the register with MOVN instead of MOVZ,
> before setting the remaining lanes with MOVK.
>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
> tcg/aarch64/tcg-target.c | 62
> ++++++++++++++++++++++++++++++++++++++----------
> 1 file changed, 49 insertions(+), 13 deletions(-)
>
> diff --git a/tcg/aarch64/tcg-target.c b/tcg/aarch64/tcg-target.c
> index 47f4708..a7b6796 100644
> --- a/tcg/aarch64/tcg-target.c
> +++ b/tcg/aarch64/tcg-target.c
> @@ -531,24 +531,60 @@ static void tcg_out_movi(TCGContext *s, TCGType type,
> TCGReg rd,
> tcg_target_long value)
> {
> AArch64Insn insn;
> -
> - if (type == TCG_TYPE_I32) {
> + int i, wantinv, shift;
> + tcg_target_long svalue = value;
> + tcg_target_long ivalue, imask;
> +
> + /* For 32-bit values, discard potential garbage in value. For 64-bit
> + values within [2**31, 2**32-1], we can create smaller sequences by
> + interpreting this as a negative 32-bit number, while ensuring that
> + the high 32 bits are cleared by setting SF=0. */
> + if (type == TCG_TYPE_I32 || (value & ~0xffffffffull) == 0) {
> + svalue = (int32_t)value;
> value = (uint32_t)value;
> + type = TCG_TYPE_I32;
> + }
> + ivalue = ~svalue;
> +
> + /* Would it take fewer insns to begin with MOVN? For the value and its
> + inverse, count the number of 16-bit lanes that are 0. */
> + for (i = wantinv = imask = 0; i < (32 << type); i += 16) {
> + tcg_target_long mask = 0xffffull << i;
> + if ((value & mask) == 0) {
> + wantinv -= 1;
> + }
> + if ((ivalue & mask) == 0) {
> + wantinv += 1;
> + imask |= mask;
> + }
> }
>
> - /* count trailing zeros in 16 bit steps, mapping 64 to 0. Emit the
> - first MOVZ with the half-word immediate skipping the zeros, with a
> shift
> - (LSL) equal to this number. Then all next instructions use MOVKs.
> - Zero the processed half-word in the value, continue until empty.
> - We build the final result 16bits at a time with up to 4 instructions,
> - but do not emit instructions for 16bit zero holes. */
> + /* If we had more 0xffff than 0x0000, invert VALUE and use MOVN. */
> insn = I3405_MOVZ;
> - do {
> - unsigned shift = ctz64(value) & (63 & -16);
> - tcg_out_insn_3405(s, insn, shift >= 32, rd, value >> shift, shift);
> + if (wantinv > 0) {
> + value = ivalue;
> + insn = I3405_MOVN;
> + }
> +
> + /* Find the lowest lane that is not 0x0000. */
> + shift = ctz64(value) & (63 & -16);
> + tcg_out_insn_3405(s, insn, type, rd, value >> shift, shift);
> +
> + if (wantinv > 0) {
> + /* Re-invert the value, so MOVK sees non-inverted bits. */
> + value = ~value;
> + /* Clear out all the 0xffff lanes. */
> + value ^= imask;
> + }
> + /* Clear out the lane that we just set. */
> + value &= ~(0xffffUL << shift);
> +
> + /* Iterate until all lanes have been set, and thus cleared from VALUE.
> */
> + while (value) {
> + shift = ctz64(value) & (63 & -16);
> + tcg_out_insn(s, 3405, MOVK, type, rd, value >> shift, shift);
> value &= ~(0xffffUL << shift);
> - insn = I3405_MOVK;
> - } while (value);
> + }
> }
>
> static inline void tcg_out_ldst_r(TCGContext *s,
>
Reviewed-by: Claudio Fontana <address@hidden>
- Re: [Qemu-devel] [PATCH 01/26] tcg-aarch64: Properly detect SIGSEGV writes, (continued)
- [Qemu-devel] [PATCH 02/26] tcg-aarch64: Use intptr_t apropriately, Richard Henderson, 2014/03/14
- [Qemu-devel] [PATCH 03/26] tcg-aarch64: Use TCGType and TCGMemOp constants, Richard Henderson, 2014/03/14
- [Qemu-devel] [PATCH 04/26] tcg-aarch64: Use MOVN in tcg_out_movi, Richard Henderson, 2014/03/14
- Re: [Qemu-devel] [PATCH 04/26] tcg-aarch64: Use MOVN in tcg_out_movi,
Claudio Fontana <=
- [Qemu-devel] [PATCH 06/26] tcg-aarch64: Special case small constants in tcg_out_movi, Richard Henderson, 2014/03/14
- [Qemu-devel] [PATCH 07/26] tcg-aarch64: Use adrp in tcg_out_movi, Richard Henderson, 2014/03/14
- [Qemu-devel] [PATCH 05/26] tcg-aarch64: Use ORRI in tcg_out_movi, Richard Henderson, 2014/03/14
- [Qemu-devel] [PATCH 08/26] tcg-aarch64: Use symbolic names for branches, Richard Henderson, 2014/03/14