On 09/12/15 17:02, Kyrill Tkachov wrote:
On 09/12/15 16:59, Evandro Menezes wrote:
On 12/09/2015 10:52 AM, Kyrill Tkachov wrote:
Hi Evandro,
On 08/12/15 21:35, Evandro Menezes wrote:
Emit square root using the Newton series
2015-12-03 Evandro Menezes <e.mene...@samsung.com>
gcc/
* config/aarch64/aarch64-protos.h (aarch64_emit_swsqrt):
Declare new
function.
* config/aarch64/aarch64-simd.md (sqrt<mode>2): New
expansion and
insn definitions.
* config/aarch64/aarch64-tuning-flags.def
(AARCH64_EXTRA_TUNE_FAST_SQRT): New tuning macro.
* config/aarch64/aarch64.c (aarch64_emit_swsqrt): Define
new function.
* config/aarch64/aarch64.md (sqrt<mode>2): New expansion
and insn
definitions.
* config/aarch64/aarch64.opt (mlow-precision-recip-sqrt):
Expand option
description.
* doc/invoke.texi (mlow-precision-recip-sqrt): Likewise.
This patch extends the patch that added support for implementing x^-1/2 using
the Newton series by adding support for x^1/2 as well.
Is it OK at this point of stage 3?
A comment on the patch itself from me...
diff --git a/gcc/config/aarch64/aarch64-tuning-flags.def
b/gcc/config/aarch64/aarch64-tuning-flags.def
index 6f7dbce..11c6c9a 100644
--- a/gcc/config/aarch64/aarch64-tuning-flags.def
+++ b/gcc/config/aarch64/aarch64-tuning-flags.def
@@ -30,4 +30,4 @@
AARCH64_EXTRA_TUNING_OPTION ("rename_fma_regs", RENAME_FMA_REGS)
AARCH64_EXTRA_TUNING_OPTION ("recip_sqrt", RECIP_SQRT)
-
+AARCH64_EXTRA_TUNING_OPTION ("fast_sqrt", FAST_SQRT)
That seems like a misleading name to me.
If we're doing this, that means that the sqrt instruction is not faster
than doing the inverse sqrt estimation followed by a multiply.
I think a name like "synth_sqrt" or "estimate_sqrt" or something along those
lines
is more appropriate.
Unfortunately, this is the case on Exynos M1: the series is faster than the instruction.
:-( So, other targets when this is also true, using the "fast_sqrt" option
might make sense.
Sure, but the way your patch is written, we will emit the series when
"fast_sqrt" is set, rather
than the other way around, unless I'm misreading the logic in:
Sorry, what I meant to say is it would be clearer, IMO, to describe the
compiler action that is being taken
(e.g. the rename_fma_regs tuning flag), in this case it's estimating sqrt using
a series.
Kyrill
diff --git a/gcc/config/aarch64/aarch64-simd.md
b/gcc/config/aarch64/aarch64-simd.md
index 030a101..f6d2da4 100644
--- a/gcc/config/aarch64/aarch64-simd.md
+++ b/gcc/config/aarch64/aarch64-simd.md
@@ -4280,7 +4280,23 @@
;; sqrt
-(define_insn "sqrt<mode>2"
+(define_expand "sqrt<mode>2"
+ [(set (match_operand:VDQF 0 "register_operand")
+ (sqrt:VDQF (match_operand:VDQF 1 "register_operand")))]
+ "TARGET_SIMD"
+{
+ if ((AARCH64_EXTRA_TUNE_FAST_SQRT & aarch64_tune_params.extra_tuning_flags)
+ && !optimize_function_for_size_p (cfun)
+ && flag_finite_math_only
+ && !flag_trapping_math
+ && flag_unsafe_math_optimizations)
+ {
+ aarch64_emit_swsqrt (operands[0], operands[1]);
+ DONE;
+ }
+})
Thanks,
Kyrill
