* SImode -> DImode optimizations
@ 2002-02-21 21:17 Alan Modra
2002-02-22 1:33 ` Richard Henderson
0 siblings, 1 reply; 2+ messages in thread
From: Alan Modra @ 2002-02-21 21:17 UTC (permalink / raw)
To: gcc
What's the correct way to let gcc know that SImode insn patterns
leave the high part of a reg in a known state? eg. powerpc has
(define_insn "rotlsi3"
[(set (match_operand:SI 0 "gpc_reg_operand" "=r")
(rotate:SI (match_operand:SI 1 "gpc_reg_operand" "r")
(match_operand:SI 2 "reg_or_cint_operand" "ri")))]
""
"{rl%I2nm|rlw%I2nm} %0,%1,%h2,0xffffffff")
On PowerPC64, this particular insn is guaranteed to leave the high
32 bits of the reg zero. I'd like to avoid gcc generating
unnecessary zero_extendsidi2 insns. I know this can be done by
writing appropriate patterns that combine both operations and emit
a single rlwinm machine insn, but that leaves the zero_extend in
the rtl. What I'm after is a way of zapping the zero_extend, so
that eg.
rotlsi3
zero_extendsidi2
cmpsi 0
is optimized into one insn in the same way as is done for
rotlsi3
cmpsi 0
Or do I have to write a bunch of 3 insn combiners?
Hmm, or something different, like specifying the output of rotlsi3
and other similar instructions is really DImode? If so, how to
do this without breaking things horribly?
--
Alan Modra
IBM OzLabs - Linux Technology Centre
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: SImode -> DImode optimizations
2002-02-21 21:17 SImode -> DImode optimizations Alan Modra
@ 2002-02-22 1:33 ` Richard Henderson
0 siblings, 0 replies; 2+ messages in thread
From: Richard Henderson @ 2002-02-22 1:33 UTC (permalink / raw)
To: gcc
On Fri, Feb 22, 2002 at 03:32:38PM +1030, Alan Modra wrote:
> What's the correct way to let gcc know that SImode insn patterns
> leave the high part of a reg in a known state?
Create additional patterns that also contain the zero_extend. I.e.
(set (match_operand:DI 0 "gpc_reg_operand" "=r")
(zero_extend:DI
(rotate:SI (match_operand:SI 1 "gpc_reg_operand" "r")
(match_operand:SI 2 "reg_or_cint_operand" "ri"))))
r~
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2002-02-21 21:17 SImode -> DImode optimizations Alan Modra
2002-02-22 1:33 ` Richard Henderson
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