On Tue, Sep 06, 2016 at 10:19:50AM +0100, James Greenhalgh wrote:
> This patch adds patterns for conversion from 64-bit integer to 16-bit
> floating-point values under AArch64 targets which don't have support for
> the ARMv8.2-A 16-bit floating point extensions.
>
> We implement these by first saturating to a SImode (we know that any
> values >= 65504 will round to infinity after conversion to HFmode), then
> converting to a DFmode (unsigned conversions could go to SFmode, but there
> is no performance benefit to this). Then converting to HFmode.
>
> Having added these patterns, the expansion path in "expand_float" will
> now try to use them for conversions from SImode to HFmode as there is no
> floatsihf2 pattern. expand_float first tries widening the integer size and
> looking for a match, so it will try SImode -> DImode. But our DI mode
> pattern is going to then saturate us back to SImode which is wasteful.
>
> Better, would be for us to provide float(uns)sihf2 patterns directly.
> So that's what this patch does.
>
> The testcase add in this patch would fail on trunk for AArch64. There is
> no libgcc routine to make the conversion, and we don't provide appropriate
> patterns in the backend, so we get a link-time error.
>
> Bootstrapped and tested on aarch64-none-linux-gnu
>
> OK for trunk?
Ping.
Thanks,
James
> 2016-09-06 James Greenhalgh <james.greenha...@arm.com>
>
> * config/aarch64/aarch64.md (<optab>sihf2): Convert to expand.
> (<optab>dihf2): Likewise.
> (aarch64_fp16_<optab><mode>hf2): New.
>
> 2016-09-06 James Greenhalgh <james.greenha...@arm.com>
>
> * gcc.target/aarch64/floatdihf2_1.c: New.
>
> diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
> index 6afaf90..1882a72 100644
> --- a/gcc/config/aarch64/aarch64.md
> +++ b/gcc/config/aarch64/aarch64.md
> @@ -4630,7 +4630,14 @@
> [(set_attr "type" "f_cvti2f")]
> )
>
> -(define_insn "<optab><mode>hf2"
> +;; If we do not have ARMv8.2-A 16-bit floating point extensions, the
> +;; midend will arrange for an SImode conversion to HFmode to first go
> +;; through DFmode, then to HFmode. But first it will try converting
> +;; to DImode then down, which would match our DImode pattern below and
> +;; give very poor code-generation. So, we must provide our own emulation
> +;; of the mid-end logic.
> +
> +(define_insn "aarch64_fp16_<optab><mode>hf2"
> [(set (match_operand:HF 0 "register_operand" "=w")
> (FLOATUORS:HF (match_operand:GPI 1 "register_operand" "r")))]
> "TARGET_FP_F16INST"
> @@ -4638,6 +4645,53 @@
> [(set_attr "type" "f_cvti2f")]
> )
>
> +(define_expand "<optab>sihf2"
> + [(set (match_operand:HF 0 "register_operand")
> + (FLOATUORS:HF (match_operand:SI 1 "register_operand")))]
> + "TARGET_FLOAT"
> +{
> + if (TARGET_FP_F16INST)
> + emit_insn (gen_aarch64_fp16_<optab>sihf2 (operands[0], operands[1]));
> + else
> + {
> + rtx convert_target = gen_reg_rtx (DFmode);
> + emit_insn (gen_<optab>sidf2 (convert_target, operands[1]));
> + emit_insn (gen_truncdfhf2 (operands[0], convert_target));
> + }
> + DONE;
> +}
> +)
> +
> +;; For DImode there is no wide enough floating-point mode that we
> +;; can convert through natively (TFmode would work, but requires a library
> +;; call). However, we know that any value >= 65504 will be rounded
> +;; to infinity on conversion. This is well within the range of SImode, so
> +;; we can:
> +;; Saturate to SImode.
> +;; Convert from that to DFmode
> +;; Convert from that to HFmode (phew!).
> +;; Note that the saturation to SImode requires the SIMD extensions. If
> +;; we ever need to provide this pattern where the SIMD extensions are not
> +;; available, we would need a different approach.
> +
> +(define_expand "<optab>dihf2"
> + [(set (match_operand:HF 0 "register_operand")
> + (FLOATUORS:HF (match_operand:DI 1 "register_operand")))]
> + "TARGET_FLOAT && (TARGET_FP_F16INST || TARGET_SIMD)"
> +{
> + if (TARGET_FP_F16INST)
> + emit_insn (gen_aarch64_fp16_<optab>dihf2 (operands[0], operands[1]));
> + else
> + {
> + rtx sat_target = gen_reg_rtx (SImode);
> + emit_insn (gen_aarch64_<su_optab>qmovndi (sat_target, operands[1]));
> + emit_insn (gen_<optab>sihf2 (operands[0], sat_target));
> + }
> +
> + DONE;
> +}
> +)
> +
> ;; Convert between fixed-point and floating-point (scalar modes)
>
> (define_insn "<FCVT_F2FIXED:fcvt_fixed_insn><GPF:mode>3"
> diff --git a/gcc/testsuite/gcc.target/aarch64/floatdihf2_1.c
> b/gcc/testsuite/gcc.target/aarch64/floatdihf2_1.c
> new file mode 100644
> index 0000000..9eaa4ba
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/floatdihf2_1.c
> @@ -0,0 +1,35 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +/* Test that conversion from 32-bit and 64-bit integers can be done
> + without a call to the support library. */
> +
> +#pragma GCC target ("arch=armv8.2-a+nofp16")
> +
> +__fp16
> +foo (int x)
> +{
> + return x;
> +}
> +
> +__fp16
> +bar (unsigned int x)
> +{
> + return x;
> +}
> +
> +__fp16
> +fool (long long x)
> +{
> + return x;
> +}
> +
> +__fp16
> +barl (unsigned long long x)
> +{
> + return x;
> +}
> +
> +
> +/* { dg-final { scan-assembler-not "__float\\\[ds\\\]ihf2" } } */
> +/* { dg-final { scan-assembler-not "__floatun\\\[ds\\\]ihf2" } } */
