public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug rtl-optimization/45215] Tree-optimization misses a trick with bit tests
[not found] <bug-45215-4@http.gcc.gnu.org/bugzilla/>
@ 2021-06-08 9:44 ` pinskia at gcc dot gnu.org
0 siblings, 0 replies; only message in thread
From: pinskia at gcc dot gnu.org @ 2021-06-08 9:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=45215
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|tree-optimization |rtl-optimization
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note on the trunk I have change the code slightly to get a cmove done.
With the cmove we could simplify the following RTL:
Trying 27, 28 -> 29:
27: {flags:CCZ=cmp(r86:SI&0x100,0);r82:SI=r86:SI&0x100;}
REG_DEAD r86:SI
28: r85:SI=0xffffffffffffffe6
29: r82:SI={(flags:CCZ==0)?r82:SI:r85:SI}
REG_DEAD r85:SI
REG_DEAD flags:CCZ
Failed to match this instruction:
(set (reg/v:SI 82 [ tt ])
(if_then_else:SI (eq (zero_extract:SI (reg:SI 86)
(const_int 1 [0x1])
(const_int 8 [0x8]))
(const_int 0 [0]))
(and:SI (reg:SI 86)
(const_int 256 [0x100]))
(const_int -26 [0xffffffffffffffe6])))
But that would be a 3->3 combine which I don't know if combine does. I know it
does 3->1 and 3->2
andl $256, %edi
movl $-26, %eax
cmovne %eax, %edi
I also don't know what the cost of doing cmov vs the shifts here though.
I know for aarch64, it is worse but that should have been modeled already.
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2021-06-08 9:44 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
[not found] <bug-45215-4@http.gcc.gnu.org/bugzilla/>
2021-06-08 9:44 ` [Bug rtl-optimization/45215] Tree-optimization misses a trick with bit tests pinskia at gcc dot gnu.org
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).