On Wed, Aug 26, 2015 at 08:40:49AM +0930, Alan Modra wrote:
> On Tue, Aug 25, 2015 at 10:08:54AM -0700, Segher Boessenkool wrote:
> > -(define_insn_and_split "*and<mode>3_imm_dot_shifted"
> > - [(set (match_operand:CC 3 "cc_reg_operand" "=x,?y")
> > +(define_insn "*and<mode>3_imm_dot_shifted"
> > + [(set (match_operand:CC 3 "cc_reg_operand" "=x")
>
> Is this really the best solution? The operand predicate allows any
> cr, but the constraint only cr0. In the past we've seen this sort of
> thing result in "insn does not satisfy its constraints" errors,
I don't think that can happen here. It is the same situation as
gpc_reg_operand with a "b" constraint.
> and if
> the operand is successfully reloaded you'll get slow mcrf insns.
What is slow about those? It's not mfcr :-)
Also note that prior compilers (at least as far back as 4.7) generated
it here, too (at -O2 etc. even).
> At
> -O1 the testcase generates:
>
> andi. 8,3,0x16
> mcrf 4,0
>
> I started throwing together a patch yesterday, before you claimed the
> bug. With this patch, I see what looks to be better code despite it
> being larger:
>
> li 9,22
> and 9,3,9
> cmpdi 4,9,0
The alternative that I was trying to avoid is
andi. 8,3,0x16
cmpdi 4,8,0
which doesn't have such a long dependency chain.
> diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
> index 87abd6e..a9eea80 100644
> --- a/gcc/config/rs6000/rs6000.md
> +++ b/gcc/config/rs6000/rs6000.md
> @@ -3060,17 +3060,18 @@
> return "#";
> }
> "&& reload_completed && cc_reg_not_cr0_operand (operands[3], CCmode)"
> - [(set (match_dup 0)
> - (and:GPR (lshiftrt:GPR (match_dup 1)
> - (match_dup 4))
> - (match_dup 2)))
> + [(set (match_dup 0) (match_dup 2))
This won't work for 0xa000 etc.
> + (set (match_dup 0) (and:GPR (match_dup 1) (match_dup 0)))
> (set (match_dup 3)
> (compare:CC (match_dup 0)
> (const_int 0)))]
> - ""
> + "
> +{
> + operands[2] = GEN_INT (UINTVAL (operands[2]) << INTVAL (operands[4]));
> +}"
> [(set_attr "type" "logical")
> (set_attr "dot" "yes")
> - (set_attr "length" "4,8")])
> + (set_attr "length" "4,12")])
Segher
