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* [Bug middle-end/55653] New: Unnecessary initialization of vector register @ 2012-12-11 19:34 josh.m.conner at gmail dot com 2012-12-11 20:06 ` [Bug middle-end/55653] " pinskia at gcc dot gnu.org ` (2 more replies) 0 siblings, 3 replies; 4+ messages in thread From: josh.m.conner at gmail dot com @ 2012-12-11 19:34 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55653 Bug #: 55653 Summary: Unnecessary initialization of vector register Classification: Unclassified Product: gcc Version: 4.8.0 Status: UNCONFIRMED Severity: enhancement Priority: P3 Component: middle-end AssignedTo: unassigned@gcc.gnu.org ReportedBy: josh.m.conner@gmail.com When initializing all lanes of a vector register, I notice that the register is first initialized to zero and then all lanes of the vector are independently initialized, resulting in extra code. Specifically, I'm looking at the aarch64 target, with the following source: void fmla_loop (double * restrict result, double * restrict mul1, double mul2, int size) { int i; for (i = 0; i < size; i++) result[i] = result[i] + mul1[i] * mul2; } Compiled with: aarch64-linux-gnu-gcc -std=c99 -O3 -ftree-vectorize -S -o test.s test.c The resultant code to initialize a vector register with two instances of mul2 is: adr x3, .LC0 ld1 {v3.2d}, [x3] ins v3.d[0], v0.d[0] ins v3.d[1], v0.d[0] ... .LC0: .word 0 .word 0 .word 0 .word 0 Where the first two instructions (that initialize the vector register) are unnecessary, as is the space for .LC0. Note that this initialization is being performed here in store_constructor: /* Inform later passes that the old value is dead. */ if (!cleared && !vector && REG_P (target)) emit_move_insn (target, CONST0_RTX (GET_MODE (target))); right after another check to see if the vector needs to be cleared out (and determine that it doesn't). Instead of the emit_move_insn, that code used to be: emit_insn (gen_rtx_CLOBBER (VOIDmode, target)); But was changed in r101169, with the comment: "The expr.c change elides an extra move that's creeped in since we changed clobbered values to get new registers in reload." (see full checkin text here: http://gcc.gnu.org/ml/gcc-patches/2005-06/msg01584.html) It's not clear to me whether this can be changed back, or if later passes should be recognizing this initialization as redundant, or whether we need a new expand pattern to match vector fill (vector duplicate). At any rate, the code is certainly not ideal as it stands. Thanks! ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/55653] Unnecessary initialization of vector register 2012-12-11 19:34 [Bug middle-end/55653] New: Unnecessary initialization of vector register josh.m.conner at gmail dot com @ 2012-12-11 20:06 ` pinskia at gcc dot gnu.org 2013-10-07 9:18 ` rearnsha at gcc dot gnu.org 2013-10-07 9:31 ` rearnsha at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: pinskia at gcc dot gnu.org @ 2012-12-11 20:06 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55653 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Keywords| |missed-optimization Target| |aarch64-*-* CC| |pinskia at gcc dot gnu.org --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-12-11 20:06:00 UTC --- I think there are two different issues here. The first issue is a target issue as {0.0, 0.0} should be done as just an xor which really resolves this issue as it is able to optimize that out (though it is a good thing to do even without the other part). The other issue shouldn't !vector be false here as we have a vector? ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/55653] Unnecessary initialization of vector register 2012-12-11 19:34 [Bug middle-end/55653] New: Unnecessary initialization of vector register josh.m.conner at gmail dot com 2012-12-11 20:06 ` [Bug middle-end/55653] " pinskia at gcc dot gnu.org @ 2013-10-07 9:18 ` rearnsha at gcc dot gnu.org 2013-10-07 9:31 ` rearnsha at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rearnsha at gcc dot gnu.org @ 2013-10-07 9:18 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55653 Richard Earnshaw <rearnsha at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |RESOLVED Resolution|--- |FIXED Target Milestone|--- |4.8.0 --- Comment #2 from Richard Earnshaw <rearnsha at gcc dot gnu.org> --- Fixed with: 2013-01-08 Tejas Belagod <tejas.belagod@arm.com> * config/aarch64/aarch64-simd.md (vec_init<mode>): New. * config/aarch64/aarch64-protos.h (aarch64_expand_vector_init): Declare. * config/aarch64/aarch64.c (aarch64_simd_dup_constant, aarch64_simd_make_constant, aarch64_expand_vector_init): New. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/55653] Unnecessary initialization of vector register 2012-12-11 19:34 [Bug middle-end/55653] New: Unnecessary initialization of vector register josh.m.conner at gmail dot com 2012-12-11 20:06 ` [Bug middle-end/55653] " pinskia at gcc dot gnu.org 2013-10-07 9:18 ` rearnsha at gcc dot gnu.org @ 2013-10-07 9:31 ` rearnsha at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rearnsha at gcc dot gnu.org @ 2013-10-07 9:31 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55653 --- Comment #3 from Richard Earnshaw <rearnsha at gcc dot gnu.org> --- On the secondary issue of initializing FP vectors to zero, we now generate for typedef double f __attribute__((vector_size(16))); f g() { f a = {0.0, 0.0}; return a; } g: movi v0.2d, 0 ret ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2013-10-07 9:31 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2012-12-11 19:34 [Bug middle-end/55653] New: Unnecessary initialization of vector register josh.m.conner at gmail dot com 2012-12-11 20:06 ` [Bug middle-end/55653] " pinskia at gcc dot gnu.org 2013-10-07 9:18 ` rearnsha at gcc dot gnu.org 2013-10-07 9:31 ` rearnsha at gcc dot gnu.org
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