On 16 August 2011 15:20, Ramana Radhakrishnan
<ramana.radhakrish...@linaro.org> wrote:
> Hi,
>
> While looking at a failure with regrename and
> mvectorize-with-neon-quad I noticed that the early-clobber in this
> vec_pack_trunc pattern is superfluous given that we can use
> reg_overlap_mentioned_p to decide in which order we want to emit these
> 2 instructions. While it works around the problem in regrename.c I
> still think that the behaviour in regrename is a bit suspicious and
> needs some more investigation.
>
RichardS finally fixed the problem in data-flow and hence we should be
able to turn on vectorize_with_quad anyway.
Here's the patch which I thought I should have committed as a
workaround but I think it's better to split this further in the case
where the 2 registers are equal because otherwise you are pointlessly
creating a stall in the Neon pipe for the vmovn result to arrive.
Hence I'm not committing this patch.
Tests finished OK btw for this patch.
cheers
Ramana
index 24dd941..2c60c5f 100644
--- a/gcc/config/arm/neon.md
+++ b/gcc/config/arm/neon.md
@@ -5631,14 +5631,29 @@
; the semantics of the instructions require.
(define_insn "vec_pack_trunc_<mode>"
- [(set (match_operand:<V_narrow_pack> 0 "register_operand" "=&w")
+ [(set (match_operand:<V_narrow_pack> 0 "register_operand" "=w")
(vec_concat:<V_narrow_pack>
(truncate:<V_narrow>
(match_operand:VN 1 "register_operand" "w"))
(truncate:<V_narrow>
(match_operand:VN 2 "register_operand" "w"))))]
"TARGET_NEON && !BYTES_BIG_ENDIAN"
- "vmovn.i<V_sz_elem>\t%e0, %q1\;vmovn.i<V_sz_elem>\t%f0, %q2"
+ {
+ /* If operand1 and operand2 are identical, then the second
+ narrowing operation isn't needed as the values obtained
+ in both parts of the destination q register are identical.
+ This precludes the need for an early clobber in the destination
+ operand. */
+ if (rtx_equal_p (operands[1], operands[2]))
+ return "vmovn.i<V_sz_elem>\\t%e0, %q1\;vmov.i<V_sz_elem>\\t%f0, %e0";
+ else
+ {
+ if (reg_overlap_mentioned_p (operands[0], operands[2]))
+ return "vmovn.i<V_sz_elem>\\t%f0, %q2\;vmovn.i<V_sz_elem>\\t%e0, %q1";
+ else
+ return "vmovn.i<V_sz_elem>\\t%e0, %q1\;vmovn.i<V_sz_elem>\\t%f0, %q2";
+ }
+ }
[(set_attr "neon_type" "neon_shift_1")
(set_attr "length" "8")]
)
