On Mon, Aug 5, 2019 at 1:50 PM Richard Biener <rguent...@suse.de> wrote:
>
> On Sun, 4 Aug 2019, Uros Bizjak wrote:
>
> > On Sat, Aug 3, 2019 at 7:26 PM Richard Biener <rguent...@suse.de> wrote:
> > >
> > > On Thu, 1 Aug 2019, Uros Bizjak wrote:
> > >
> > > > On Thu, Aug 1, 2019 at 11:28 AM Richard Biener <rguent...@suse.de>
> > > > wrote:
> > > >
> > > >>>> So you unconditionally add a smaxdi3 pattern - indeed this looks
> > > >>>> necessary even when going the STV route. The actual regression
> > > >>>> for the testcase could also be solved by turing the smaxsi3
> > > >>>> back into a compare and jump rather than a conditional move sequence.
> > > >>>> So I wonder how you'd do that given that there's pass_if_after_reload
> > > >>>> after pass_split_after_reload and I'm not sure we can split
> > > >>>> as late as pass_split_before_sched2 (there's also a split _after_
> > > >>>> sched2 on x86 it seems).
> > > >>>>
> > > >>>> So how would you go implement {s,u}{min,max}{si,di}3 for the
> > > >>>> case STV doesn't end up doing any transform?
> > > >>>
> > > >>> If STV doesn't transform the insn, then a pre-reload splitter splits
> > > >>> the insn back to compare+cmove.
> > > >>
> > > >> OK, that would work. But there's no way to force a jumpy sequence then
> > > >> which we know is faster than compare+cmove because later RTL
> > > >> if-conversion passes happily re-discover the smax (or conditional move)
> > > >> sequence.
> > > >>
> > > >>> However, considering the SImode move
> > > >>> from/to int/xmm register is relatively cheap, the cost function should
> > > >>> be tuned so that STV always converts smaxsi3 pattern.
> > > >>
> > > >> Note that on both Zen and even more so bdverN the int/xmm transition
> > > >> makes it no longer profitable but a _lot_ slower than the cmp/cmov
> > > >> sequence... (for the loop in hmmer which is the only one I see
> > > >> any effect of any of my patches). So identifying chains that
> > > >> start/end in memory is important for cost reasons.
> > > >
> > > > Please note that the cost function also considers the cost of move
> > > > from/to xmm. So, the cost of the whole chain would disable the
> > > > transformation.
> > > >
> > > >> So I think the splitting has to happen after the last if-conversion
> > > >> pass (and thus we may need to allocate a scratch register for this
> > > >> purpose?)
> > > >
> > > > I really hope that the underlying issue will be solved by a machine
> > > > dependant pass inserted somewhere after the pre-reload split. This
> > > > way, we can split unconverted smax to the cmove, and this later pass
> > > > would handle jcc and cmove instructions. Until then... yes your
> > > > proposed approach is one of the ways to avoid unwanted if-conversion,
> > > > although sometimes we would like to split to cmove instead.
> > >
> > > So the following makes STV also consider SImode chains, re-using the
> > > DImode chain code. I've kept a simple incomplete smaxsi3 pattern
> > > and also did not alter the {SI,DI}mode chain cost function - it's
> > > quite off for TARGET_64BIT. With this I get the expected conversion
> > > for the testcase derived from hmmer.
> > >
> > > No further testing sofar.
> > >
> > > Is it OK to re-use the DImode chain code this way? I'll clean things
> > > up some more of course.
> >
> > Yes, the approach looks OK to me. It makes chain building mode
> > agnostic, and the chain building can be used for
> > a) DImode x86_32 (as is now), but maybe 64bit minmax operation can be added.
> > b) SImode x86_32 and x86_64 (this will be mainly used for SImode
> > minmax and surrounding SImode operations)
> > c) DImode x86_64 (also, mainly used for DImode minmax and surrounding
> > DImode operations)
> >
> > > Still need help with the actual patterns for minmax and how the splitters
> > > should look like.
> >
> > Please look at the attached patch. Maybe we can add memory_operand as
> > operand 1 and operand 2 predicate, but let's keep things simple for
> > now.
>
> Thanks. The attached patch makes the patch cleaner and it survives
> "some" barebone testing. It also touches the cost function to
> avoid being too overly trigger-happy. I've also ended up using
> ix86_cost->sse_op instead of COSTS_N_INSN-based magic. In
> particular we estimated GPR reg-reg move as COST_N_INSNS(2) while
> move costs shouldn't be wrapped in COST_N_INSNS.
> IMHO we should probably disregard any reg-reg moves for costing pre-RA.
> At least with the current code every reg-reg move biases in favor of
> SSE...
This is currently a bit mixed-up area in x86 target support. HJ is
looking into this [1] and I hope Honza can review the patch.
> And we're simply adding move and non-move costs in 'gain', somewhat
> mixing apples and oranges? We could separate those and require
> both to be a net positive win?
>
> Still using -mtune=bdverN exposes that some cost tables have xmm and gpr
> costs as apples and oranges... (so it never triggers for Bulldozer)
>
> I now run into
>
> /space/rguenther/src/svn/trunk-bisect/libgcc/libgcov-driver.c:509:1:
> error: unrecognizable insn:
> (insn 116 115 1511 8 (set (subreg:V2DI (reg/v:DI 87 [ run_max ]) 0)
> (smax:V2DI (subreg:V2DI (reg/v:DI 87 [ run_max ]) 0)
> (subreg:V2DI (reg:DI 349 [ MEM[base: _261, offset: 0B] ]) 0)))
> -1
> (expr_list:REG_DEAD (reg:DI 349 [ MEM[base: _261, offset: 0B] ])
> (expr_list:REG_UNUSED (reg:CC 17 flags)
> (nil))))
> during RTL pass: stv
>
> where even with -mavx2 we do not have s{min,max}v2di3. We do have
> an expander here but it seems only AVX512F has the DImode min/max
> ops. I have adjusted dimode_scalar_to_vector_candidate_p
> accordingly.
>
> I'm considering to rename the
> dimode_{scalar_to_vector_candidate_p,remove_non_convertible_regs}
> functions to drop the dimode_ prefix - is that OK or do you
> prefer some other prefix?
>
> So - bootstrap with --with-arch=skylake in progress.
>
> It detects quite a few chains (unsurprisingly) so I guess we need
> to address compile-time issues in the pass before enabling this
> enhancement (maybe as followup?).
>
> Further comments on the actual patch welcome, I consider it
> "finished" if testing reveals no issues. ChangeLog still needs
> to be written and testcases to be added.
> +;; min/max patterns
> +
> +(define_code_attr smaxmin_rel [(smax "ge") (smin "le")])
> +
> +(define_insn_and_split "<code><mode>3"
> + [(set (match_operand:SWI48 0 "register_operand")
> + (smaxmin:SWI48 (match_operand:SWI48 1 "register_operand")
> + (match_operand:SWI48 2 "register_operand")))
> + (clobber (reg:CC FLAGS_REG))]
> + "TARGET_STV && TARGET_SSE4_1
> + && can_create_pseudo_p ()"
> + "#"
> + "&& 1"
> + [(set (reg:CCGC FLAGS_REG)
> + (compare:CCGC (match_dup 1)(match_dup 2)))
> + (set (match_dup 0)
> + (if_then_else:SWI48
> + (<smaxmin_rel> (reg:CCGC FLAGS_REG)(const_int 0))
> + (match_dup 1)
> + (match_dup 2)))])
> +
> ;; Conditional addition patterns
> (define_expand "add<mode>cc"
> [(match_operand:SWI 0 "register_operand")
Please find attached (untested) i386.md patch that defines signed and
unsigned min/max pattern.
[1] https://gcc.gnu.org/ml/gcc-patches/2019-07/msg01542.html
Uros.
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index e19a591fa9d..8a492626103 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -17721,6 +17721,30 @@
std::swap (operands[4], operands[5]);
})
+;; min/max patterns
+
+(define_code_attr maxmin_rel
+ [(smax "ge") (smin "le") (umax "geu") (umin "leu")])
+(define_code_attr maxmin_cmpmode
+ [(smax "CCGC") (smin "CCGC") (umax "CC") (umin "CC")])
+
+(define_insn_and_split "<code><mode>3"
+ [(set (match_operand:SWI48 0 "register_operand")
+ (maxmin:SWI48 (match_operand:SWI48 1 "register_operand")
+ (match_operand:SWI48 2 "register_operand")))
+ (clobber (reg:CC FLAGS_REG))]
+ "TARGET_STV && TARGET_SSE4_1
+ && can_create_pseudo_p ()"
+ "#"
+ "&& 1"
+ [(set (reg:<maxmin_cmpmode> FLAGS_REG)
+ (compare:<maxmin_cmpmode> (match_dup 1)(match_dup 2)))
+ (set (match_dup 0)
+ (if_then_else:SWI48
+ (<maxmin_rel> (reg:<maxmin_cmpmode> FLAGS_REG)(const_int 0))
+ (match_dup 1)
+ (match_dup 2)))])
+
;; Conditional addition patterns
(define_expand "add<mode>cc"
[(match_operand:SWI 0 "register_operand")
