* [RFC] Induction variable candidates not sufficiently general
@ 2018-07-12 22:05 Kelvin Nilsen
2018-07-13 6:50 ` Richard Biener
2018-07-14 2:14 ` Bin.Cheng
0 siblings, 2 replies; 6+ messages in thread
From: Kelvin Nilsen @ 2018-07-12 22:05 UTC (permalink / raw)
To: gcc-patches
A somewhat old "issue report" pointed me to the code generated for a 4-fold manually unrolled version of the following loop:
> while (++len != len_limit) /* this is loop */
> if (pb[len] != cur[len])
> break;
As unrolled, the loop appears as:
> while (++len != len_limit) /* this is loop */ {
> if (pb[len] != cur[len])
> break;
> if (++len == len_limit) /* unrolled 2nd iteration */
> break;
> if (pb[len] != cur[len])
> break;
> if (++len == len_limit) /* unrolled 3rd iteration */
> break;
> if (pb[len] != cur[len])
> break;
> if (++len == len_limit) /* unrolled 4th iteration */
> break;
> if (pb[len] != cur[len])
> break;
> }
In examining the behavior of tree-ssa-loop-ivopts.c, I've discovered the only induction variable candidates that are being considered are all forms of the len variable. We are not considering any induction variables to represent the address expressions &pb[len] and &cur[len].
I rewrote the source code for this loop to make the addressing expressions more explicit, as in the following:
> cur++;
> while (++pb != last_pb) /* this is loop */ {
> if (*pb != *cur)
> break;
> ++cur;
> if (++pb == last_pb) /* unrolled 2nd iteration */
> break;
> if (*pb != *cur)
> break;
> ++cur;
> if (++pb == last_pb) /* unrolled 3rd iteration */
> break;
> if (*pb != *cur)
> break;
> ++cur;
> if (++pb == last_pb) /* unrolled 4th iteration */
> break;
> if (*pb != *cur)
> break;
> ++cur;
> }
Now, gcc does a better job of identifying the "address expression induction variables". This version of the loop runs about 10% faster than the original on my target architecture.
This would seem to be a textbook pattern for the induction variable analysis. Does anyone have any thoughts on the best way to add these candidates to the set of induction variables that are considered by tree-ssa-loop-ivopts.c?
Thanks in advance for any suggestions.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [RFC] Induction variable candidates not sufficiently general
2018-07-12 22:05 [RFC] Induction variable candidates not sufficiently general Kelvin Nilsen
@ 2018-07-13 6:50 ` Richard Biener
2018-07-14 2:14 ` Bin.Cheng
1 sibling, 0 replies; 6+ messages in thread
From: Richard Biener @ 2018-07-13 6:50 UTC (permalink / raw)
To: kdnilsen, Amker.Cheng; +Cc: GCC Patches
On Fri, Jul 13, 2018 at 12:05 AM Kelvin Nilsen <kdnilsen@linux.ibm.com> wrote:
>
> A somewhat old "issue report" pointed me to the code generated for a 4-fold manually unrolled version of the following loop:
>
> > while (++len != len_limit) /* this is loop */
> > if (pb[len] != cur[len])
> > break;
>
> As unrolled, the loop appears as:
>
> > while (++len != len_limit) /* this is loop */ {
> > if (pb[len] != cur[len])
> > break;
> > if (++len == len_limit) /* unrolled 2nd iteration */
> > break;
> > if (pb[len] != cur[len])
> > break;
> > if (++len == len_limit) /* unrolled 3rd iteration */
> > break;
> > if (pb[len] != cur[len])
> > break;
> > if (++len == len_limit) /* unrolled 4th iteration */
> > break;
> > if (pb[len] != cur[len])
> > break;
> > }
>
> In examining the behavior of tree-ssa-loop-ivopts.c, I've discovered the only induction variable candidates that are being considered are all forms of the len variable. We are not considering any induction variables to represent the address expressions &pb[len] and &cur[len].
I am surprised - did you dig down why? Because generally IVOPTs does
consider pointer IVs.
Richard.
> I rewrote the source code for this loop to make the addressing expressions more explicit, as in the following:
>
> > cur++;
> > while (++pb != last_pb) /* this is loop */ {
> > if (*pb != *cur)
> > break;
> > ++cur;
> > if (++pb == last_pb) /* unrolled 2nd iteration */
> > break;
> > if (*pb != *cur)
> > break;
> > ++cur;
> > if (++pb == last_pb) /* unrolled 3rd iteration */
> > break;
> > if (*pb != *cur)
> > break;
> > ++cur;
> > if (++pb == last_pb) /* unrolled 4th iteration */
> > break;
> > if (*pb != *cur)
> > break;
> > ++cur;
> > }
>
> Now, gcc does a better job of identifying the "address expression induction variables". This version of the loop runs about 10% faster than the original on my target architecture.
>
> This would seem to be a textbook pattern for the induction variable analysis. Does anyone have any thoughts on the best way to add these candidates to the set of induction variables that are considered by tree-ssa-loop-ivopts.c?
>
> Thanks in advance for any suggestions.
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [RFC] Induction variable candidates not sufficiently general
2018-07-12 22:05 [RFC] Induction variable candidates not sufficiently general Kelvin Nilsen
2018-07-13 6:50 ` Richard Biener
@ 2018-07-14 2:14 ` Bin.Cheng
2018-07-16 18:09 ` Kelvin Nilsen
1 sibling, 1 reply; 6+ messages in thread
From: Bin.Cheng @ 2018-07-14 2:14 UTC (permalink / raw)
To: Kelvin Nilsen; +Cc: gcc-patches List
On Fri, Jul 13, 2018 at 6:04 AM, Kelvin Nilsen <kdnilsen@linux.ibm.com> wrote:
> A somewhat old "issue report" pointed me to the code generated for a 4-fold manually unrolled version of the following loop:
>
>> while (++len != len_limit) /* this is loop */
>> if (pb[len] != cur[len])
>> break;
>
> As unrolled, the loop appears as:
>
>> while (++len != len_limit) /* this is loop */ {
>> if (pb[len] != cur[len])
>> break;
>> if (++len == len_limit) /* unrolled 2nd iteration */
>> break;
>> if (pb[len] != cur[len])
>> break;
>> if (++len == len_limit) /* unrolled 3rd iteration */
>> break;
>> if (pb[len] != cur[len])
>> break;
>> if (++len == len_limit) /* unrolled 4th iteration */
>> break;
>> if (pb[len] != cur[len])
>> break;
>> }
>
> In examining the behavior of tree-ssa-loop-ivopts.c, I've discovered the only induction variable candidates that are being considered are all forms of the len variable. We are not considering any induction variables to represent the address expressions &pb[len] and &cur[len].
>
> I rewrote the source code for this loop to make the addressing expressions more explicit, as in the following:
>
>> cur++;
>> while (++pb != last_pb) /* this is loop */ {
>> if (*pb != *cur)
>> break;
>> ++cur;
>> if (++pb == last_pb) /* unrolled 2nd iteration */
>> break;
>> if (*pb != *cur)
>> break;
>> ++cur;
>> if (++pb == last_pb) /* unrolled 3rd iteration */
>> break;
>> if (*pb != *cur)
>> break;
>> ++cur;
>> if (++pb == last_pb) /* unrolled 4th iteration */
>> break;
>> if (*pb != *cur)
>> break;
>> ++cur;
>> }
>
> Now, gcc does a better job of identifying the "address expression induction variables". This version of the loop runs about 10% faster than the original on my target architecture.
>
> This would seem to be a textbook pattern for the induction variable analysis. Does anyone have any thoughts on the best way to add these candidates to the set of induction variables that are considered by tree-ssa-loop-ivopts.c?
>
> Thanks in advance for any suggestions.
>
Hi,
Could you please file a bug with your original slow test code
attached? I tried to construct meaningful test case from your code
snippet but not successful. There is difference in generated
assembly, but it's not that fundamental. So a bug with preprocessed
test would be high appreciated.
I think there are two potential issues in cost computation for such
case: invariant expression and iv uses outside of loop handled as
inside uses.
Thanks,
bin
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [RFC] Induction variable candidates not sufficiently general
2018-07-14 2:14 ` Bin.Cheng
@ 2018-07-16 18:09 ` Kelvin Nilsen
2018-07-21 1:28 ` Bin.Cheng
0 siblings, 1 reply; 6+ messages in thread
From: Kelvin Nilsen @ 2018-07-16 18:09 UTC (permalink / raw)
To: Bin.Cheng; +Cc: gcc-patches List
[-- Attachment #1: Type: text/plain, Size: 3819 bytes --]
Thanks for looking at this for me. In simplifying the test case for a bug report, I've narrowed the "problem" to integer overflow considerations. My len variable is declared int, and the target has 64-bit pointers. I'm gathering that the "manual transformation" I quoted below is not considered "equivalent" to the original source code due to different integer overflow behaviors. If I redeclare len to be unsigned long long, then I automatically get the optimizations that I was originally expecting.
I suppose this is really NOT a bug?
Is there a compiler optimization flag that allows the optimizer to ignore array index integer overflow in considering legal optimizations?
On 7/13/18 9:14 PM, Bin.Cheng wrote:
> On Fri, Jul 13, 2018 at 6:04 AM, Kelvin Nilsen <kdnilsen@linux.ibm.com> wrote:
>> A somewhat old "issue report" pointed me to the code generated for a 4-fold manually unrolled version of the following loop:
>>
>>> while (++len != len_limit) /* this is loop */
>>> if (pb[len] != cur[len])
>>> break;
>>
>> As unrolled, the loop appears as:
>>
>>> while (++len != len_limit) /* this is loop */ {
>>> if (pb[len] != cur[len])
>>> break;
>>> if (++len == len_limit) /* unrolled 2nd iteration */
>>> break;
>>> if (pb[len] != cur[len])
>>> break;
>>> if (++len == len_limit) /* unrolled 3rd iteration */
>>> break;
>>> if (pb[len] != cur[len])
>>> break;
>>> if (++len == len_limit) /* unrolled 4th iteration */
>>> break;
>>> if (pb[len] != cur[len])
>>> break;
>>> }
>>
>> In examining the behavior of tree-ssa-loop-ivopts.c, I've discovered the only induction variable candidates that are being considered are all forms of the len variable. We are not considering any induction variables to represent the address expressions &pb[len] and &cur[len].
>>
>> I rewrote the source code for this loop to make the addressing expressions more explicit, as in the following:
>>
>>> cur++;
>>> while (++pb != last_pb) /* this is loop */ {
>>> if (*pb != *cur)
>>> break;
>>> ++cur;
>>> if (++pb == last_pb) /* unrolled 2nd iteration */
>>> break;
>>> if (*pb != *cur)
>>> break;
>>> ++cur;
>>> if (++pb == last_pb) /* unrolled 3rd iteration */
>>> break;
>>> if (*pb != *cur)
>>> break;
>>> ++cur;
>>> if (++pb == last_pb) /* unrolled 4th iteration */
>>> break;
>>> if (*pb != *cur)
>>> break;
>>> ++cur;
>>> }
>>
>> Now, gcc does a better job of identifying the "address expression induction variables". This version of the loop runs about 10% faster than the original on my target architecture.
>>
>> This would seem to be a textbook pattern for the induction variable analysis. Does anyone have any thoughts on the best way to add these candidates to the set of induction variables that are considered by tree-ssa-loop-ivopts.c?
>>
>> Thanks in advance for any suggestions.
>>
> Hi,
> Could you please file a bug with your original slow test code
> attached? I tried to construct meaningful test case from your code
> snippet but not successful. There is difference in generated
> assembly, but it's not that fundamental. So a bug with preprocessed
> test would be high appreciated.
> I think there are two potential issues in cost computation for such
> case: invariant expression and iv uses outside of loop handled as
> inside uses.
>
> Thanks,
> bin
>
>
[-- Attachment #2: ivsimple.long.c --]
[-- Type: text/plain, Size: 872 bytes --]
#include <stdlib.h>
#include <string.h>
int
bt_skip_func(const __uint64_t len_limit, const __uint8_t *cur,
long long int delta, __uint64_t len) {
const __uint8_t *pb = cur - delta;
while (++len != len_limit) {
if (pb[len] != cur[len])
break;
if (++len == len_limit)
break;
if (pb[len] != cur[len])
break;
if (++len == len_limit)
break;
if (pb[len] != cur[len])
break;
if (++len == len_limit)
break;
if (pb[len] != cur[len])
break;
}
return len;
}
int main (int argc, char *argv[]) {
char *text_input = "ttttttttttttttttthis is some text that should be longer";
unsigned long long int len_limit = strlen (text_input);
int pos = 0;
int cur_match = 0;
int depth = 0;
int result = bt_skip_func(len_limit, text_input + 3, (long long) 3,
(unsigned long long) 1);
}
[-- Attachment #3: ivsimple.long.s --]
[-- Type: text/plain, Size: 3914 bytes --]
.file "ivsimple.long.c"
.abiversion 2
.section ".text"
.align 2
.p2align 4,,15
.globl bt_skip_func
.type bt_skip_func, @function
bt_skip_func:
.LFB22:
.cfi_startproc
subf 5,5,4 # 13 [c=4 l=4] *subfdi3
std 28,-32(1) # 107 [c=4 l=4] *movdi_internal64/0
std 29,-24(1) # 108 [c=4 l=4] *movdi_internal64/0
addi 8,6,1 # 14 [c=4 l=4] *adddi3/1
std 30,-16(1) # 109 [c=4 l=4] *movdi_internal64/0
std 31,-8(1) # 110 [c=4 l=4] *movdi_internal64/0
.cfi_offset 28, -32
.cfi_offset 29, -24
.cfi_offset 30, -16
.cfi_offset 31, -8
addi 12,5,1 # 18 [c=4 l=4] *adddi3/1
addi 30,5,2 # 29 [c=4 l=4] *adddi3/1
addi 28,5,3 # 40 [c=4 l=4] *adddi3/1
addi 11,4,1 # 19 [c=4 l=4] *adddi3/1
addi 31,4,2 # 30 [c=4 l=4] *adddi3/1
addi 29,4,3 # 41 [c=4 l=4] *adddi3/1
b .L2 # 153 [c=4 l=4] jump
.p2align 4,,15
.L4:
lbzx 10,12,6 # 20 [c=8 l=4] zero_extendqisi2/0
lbzx 7,11,6 # 21 [c=8 l=4] zero_extendqisi2/0
cmpw 7,10,7 # 22 [c=4 l=4] *cmpsi_signed
bne 7,.L5 # 23 [c=4 l=4] *rs6000.md:12311
beq 5,.L3 # 27 [c=4 l=4] *rs6000.md:12311
lbzx 10,30,6 # 31 [c=8 l=4] zero_extendqisi2/0
lbzx 7,31,6 # 32 [c=8 l=4] zero_extendqisi2/0
addi 8,8,4 # 51 [c=4 l=4] *adddi3/1
cmpw 7,10,7 # 33 [c=4 l=4] *cmpsi_signed
bne 7,.L3 # 34 [c=4 l=4] *rs6000.md:12311
addi 9,6,3 # 36 [c=4 l=4] *adddi3/1
cmpld 7,3,9 # 37 [c=4 l=4] *cmpdi_unsigned
beq 7,.L3 # 38 [c=4 l=4] *rs6000.md:12311
lbzx 10,28,6 # 42 [c=8 l=4] zero_extendqisi2/0
lbzx 7,29,6 # 43 [c=8 l=4] zero_extendqisi2/0
addi 6,6,4 # 47 [c=4 l=4] *adddi3/1
cmpld 5,3,6 # 48 [c=4 l=4] *cmpdi_unsigned
cmpw 7,10,7 # 44 [c=4 l=4] *cmpsi_signed
bne 7,.L3 # 45 [c=4 l=4] *rs6000.md:12311
beq 5,.L6 # 49 [c=4 l=4] *rs6000.md:12311
lbzx 9,5,6 # 52 [c=8 l=4] zero_extendqisi2/0
lbzx 10,4,6 # 53 [c=8 l=4] zero_extendqisi2/0
cmpw 7,9,10 # 54 [c=4 l=4] *cmpsi_signed
bne 7,.L7 # 55 [c=4 l=4] *rs6000.md:12311
.L2:
cmpld 7,3,8 # 59 [c=4 l=4] *cmpdi_unsigned
addi 9,6,2 # 25 [c=4 l=4] *adddi3/1
cmpld 5,3,9 # 26 [c=4 l=4] *cmpdi_unsigned
bne 7,.L4 # 60 [c=4 l=4] *rs6000.md:12311
.L6:
mr 9,3 # 7 [c=4 l=4] *movdi_internal64/2
.L3:
ld 28,-32(1) # 113 [c=8 l=4] *movdi_internal64/1
ld 29,-24(1) # 114 [c=8 l=4] *movdi_internal64/1
ld 30,-16(1) # 115 [c=8 l=4] *movdi_internal64/1
ld 31,-8(1) # 116 [c=8 l=4] *movdi_internal64/1
extsw 3,9 # 69 [c=4 l=4] extendsidi2/1
.cfi_remember_state
.cfi_restore 31
.cfi_restore 30
.cfi_restore 29
.cfi_restore 28
blr # 118 [c=4 l=4] simple_return
.p2align 4,,15
.L5:
.cfi_restore_state
ld 28,-32(1) # 131 [c=8 l=4] *movdi_internal64/1
ld 29,-24(1) # 132 [c=8 l=4] *movdi_internal64/1
ld 30,-16(1) # 133 [c=8 l=4] *movdi_internal64/1
ld 31,-8(1) # 134 [c=8 l=4] *movdi_internal64/1
mr 9,8 # 8 [c=4 l=4] *movdi_internal64/2
extsw 3,9 # 128 [c=4 l=4] extendsidi2/1
.cfi_remember_state
.cfi_restore 31
.cfi_restore 30
.cfi_restore 29
.cfi_restore 28
blr # 136 [c=4 l=4] simple_return
.p2align 4,,15
.L7:
.cfi_restore_state
ld 28,-32(1) # 144 [c=8 l=4] *movdi_internal64/1
ld 29,-24(1) # 145 [c=8 l=4] *movdi_internal64/1
ld 30,-16(1) # 146 [c=8 l=4] *movdi_internal64/1
ld 31,-8(1) # 147 [c=8 l=4] *movdi_internal64/1
mr 9,6 # 9 [c=4 l=4] *movdi_internal64/2
extsw 3,9 # 141 [c=4 l=4] extendsidi2/1
.cfi_restore 31
.cfi_restore 30
.cfi_restore 29
.cfi_restore 28
blr # 149 [c=4 l=4] simple_return
.long 0
.byte 0,0,0,0,0,4,0,0
.cfi_endproc
.LFE22:
.size bt_skip_func,.-bt_skip_func
.section .text.startup,"ax",@progbits
.align 2
.p2align 4,,15
.globl main
.type main, @function
main:
.LFB23:
.cfi_startproc
li 3,0 # 11 [c=4 l=4] *movdi_internal64/3
blr # 18 [c=4 l=4] simple_return
.long 0
.byte 0,0,0,0,0,0,0,0
.cfi_endproc
.LFE23:
.size main,.-main
.ident "GCC: (GNU) 9.0.0 20180716 (experimental)"
.section .note.GNU-stack,"",@progbits
[-- Attachment #4: ivsimple.transformed.s --]
[-- Type: text/plain, Size: 3645 bytes --]
.file "ivsimple.transformed.c"
.abiversion 2
.section ".text"
.align 2
.p2align 4,,15
.globl bt_skip_func
.type bt_skip_func, @function
bt_skip_func:
.LFB22:
.cfi_startproc
subf 5,5,4 # 13 [c=4 l=4] *subfdi3
addi 9,6,1 # 18 [c=4 l=4] *adddi3/1
add 3,5,3 # 14 [c=4 l=4] *adddi3/0
add 9,5,9 # 19 [c=4 l=4] *adddi3/0
cmpld 7,3,9 # 20 [c=4 l=4] *cmpdi_unsigned
addi 6,6,1 # 15 [c=4 l=4] *addsi3/1
rldicl 6,6,0,32 # 16 [c=4 l=4] zero_extendsidi2/1
add 4,4,6 # 17 [c=4 l=4] *adddi3/0
bne 7,.L3 # 21 [c=4 l=4] *rs6000.md:12311
b .L6 # 124 [c=4 l=4] jump
.p2align 4,,15
.L9:
beq 5,.L2 # 31 [c=4 l=4] *rs6000.md:12311
lbz 8,1(9) # 33 [c=8 l=4] zero_extendqisi2/0
lbz 7,1(4) # 34 [c=8 l=4] zero_extendqisi2/0
cmpw 7,8,7 # 35 [c=4 l=4] *cmpsi_signed
bne 7,.L2 # 36 [c=4 l=4] *rs6000.md:12311
addi 10,9,2 # 38 [c=4 l=4] *adddi3/1
cmpld 7,3,10 # 39 [c=4 l=4] *cmpdi_unsigned
beq 7,.L2 # 40 [c=4 l=4] *rs6000.md:12311
lbz 8,2(9) # 42 [c=8 l=4] zero_extendqisi2/0
lbz 7,2(4) # 43 [c=8 l=4] zero_extendqisi2/0
cmpw 7,8,7 # 44 [c=4 l=4] *cmpsi_signed
bne 7,.L2 # 45 [c=4 l=4] *rs6000.md:12311
addi 10,9,3 # 47 [c=4 l=4] *adddi3/1
cmpld 7,10,3 # 48 [c=4 l=4] *cmpdi_unsigned
beq 7,.L6 # 49 [c=4 l=4] *rs6000.md:12311
lbz 8,3(9) # 51 [c=8 l=4] zero_extendqisi2/0
lbz 7,3(4) # 52 [c=8 l=4] zero_extendqisi2/0
addi 9,9,4 # 57 [c=4 l=4] *adddi3/1
addi 4,4,4 # 56 [c=4 l=4] *adddi3/1
cmpld 5,3,9 # 59 [c=4 l=4] *cmpdi_unsigned
cmpw 7,8,7 # 53 [c=4 l=4] *cmpsi_signed
bne 7,.L2 # 54 [c=4 l=4] *rs6000.md:12311
beq 5,.L6 # 60 [c=4 l=4] *rs6000.md:12311
.L3:
lbz 8,0(9) # 23 [c=8 l=4] zero_extendqisi2/0
lbz 7,0(4) # 24 [c=8 l=4] zero_extendqisi2/0
addi 10,9,1 # 29 [c=4 l=4] *adddi3/1
cmpld 5,3,10 # 30 [c=4 l=4] *cmpdi_unsigned
cmpw 7,8,7 # 25 [c=4 l=4] *cmpsi_signed
beq 7,.L9 # 26 [c=4 l=4] *rs6000.md:12311
mr 10,9 # 7 [c=4 l=4] *movdi_internal64/2
.L2:
subf 3,5,10 # 63 [c=4 l=4] *subfdi3
extsw 3,3 # 70 [c=4 l=4] extendsidi2/1
blr # 104 [c=4 l=4] simple_return
.p2align 4,,15
.L6:
mr 10,3 # 9 [c=4 l=4] *movdi_internal64/2
subf 3,5,10 # 115 [c=4 l=4] *subfdi3
extsw 3,3 # 116 [c=4 l=4] extendsidi2/1
blr # 119 [c=4 l=4] simple_return
.long 0
.byte 0,0,0,0,0,0,0,0
.cfi_endproc
.LFE22:
.size bt_skip_func,.-bt_skip_func
.section ".toc","aw"
.align 3
.LC1:
.quad .LC0+3
.section .text.startup,"ax",@progbits
.align 2
.p2align 4,,15
.globl main
.type main, @function
main:
.LFB23:
.cfi_startproc
.LCF1:
0: addis 2,12,.TOC.-.LCF1@ha
addi 2,2,.TOC.-.LCF1@l
.localentry main,.-main
mflr 0 # 23 [c=4 l=4] *movdi_internal64/21
addis 4,2,.LC1@toc@ha # 35 [c=12 l=8] fusion_gpr_load_di
ld 4,.LC1@toc@l(4)
li 6,1 # 8 [c=4 l=4] *movdi_internal64/3
li 5,3 # 9 [c=4 l=4] *movdi_internal64/3
li 3,55 # 11 [c=4 l=4] *movdi_internal64/3
std 0,16(1) # 24 [c=4 l=4] *movdi_internal64/0
stdu 1,-32(1) # 25 [c=4 l=4] movdi_di_update/1
.cfi_def_cfa_offset 32
.cfi_offset 65, 16
bl bt_skip_func # 12 [c=4 l=4] *call_value_local_aixdi
addi 1,1,32 # 28 [c=4 l=4] *adddi3/1
.cfi_def_cfa_offset 0
li 3,0 # 17 [c=4 l=4] *movdi_internal64/3
ld 0,16(1) # 29 [c=8 l=4] *movdi_internal64/1
mtlr 0 # 30 [c=4 l=4] *movdi_internal64/22
.cfi_restore 65
blr # 31 [c=4 l=4] simple_return
.long 0
.byte 0,0,0,1,128,0,0,0
.cfi_endproc
.LFE23:
.size main,.-main
.section .rodata.str1.8,"aMS",@progbits,1
.align 3
.LC0:
.string "ttttttttttttttttthis is some text that should be longer"
.ident "GCC: (GNU) 9.0.0 20180716 (experimental)"
.section .note.GNU-stack,"",@progbits
[-- Attachment #5: ivsimple.transformed.c --]
[-- Type: text/plain, Size: 1008 bytes --]
#include <stdlib.h>
#include <string.h>
int
bt_skip_func(const __uint32_t len_limit, const __uint8_t *cur,
int delta, __uint32_t len) {
const __uint8_t *pb = cur - delta;
const __uint8_t *orig_pb = pb;
const __uint8_t *last_pb = pb + len_limit;
pb += len;
cur += len + 1;
while (++pb != last_pb) {
if (*pb != *cur)
break;
cur++; /* 2nd iteration */
if (++pb == last_pb)
break;
if (*pb != *cur)
break;
cur++; /* 3rd iteration */
if (++pb == last_pb)
break;
if (*pb != *cur)
break;
cur++; /* 4th iteration */
if (++pb == last_pb)
break;
if (*pb != *cur)
break;
cur++; /* 4th iteration */
}
return pb - orig_pb;
}
int main (int argc, char *argv[]) {
char *text_input = "ttttttttttttttttthis is some text that should be longer";
int len_limit = strlen (text_input);
int pos = 0;
int cur_match = 0;
int depth = 0;
int result = bt_skip_func(len_limit, text_input + 3, 3, 1);
}
[-- Attachment #6: ivsimple.s --]
[-- Type: text/plain, Size: 3636 bytes --]
.file "ivsimple.c"
.abiversion 2
.section ".text"
.align 2
.p2align 4,,15
.globl bt_skip_func
.type bt_skip_func, @function
bt_skip_func:
.LFB22:
.cfi_startproc
addi 10,6,1 # 14 [c=4 l=4] *addsi3/1
subf 5,5,4 # 13 [c=4 l=4] *subfdi3
rldicl 10,10,0,32 # 15 [c=4 l=4] zero_extendsidi2/1
b .L2 # 128 [c=4 l=4] jump
.p2align 4,,15
.L4:
lbzx 8,5,10 # 20 [c=8 l=4] zero_extendqisi2/0
lbzx 11,4,10 # 21 [c=8 l=4] zero_extendqisi2/0
cmpw 7,8,11 # 22 [c=4 l=4] *cmpsi_signed
bne 7,.L5 # 23 [c=4 l=4] *rs6000.md:12311
beq 5,.L3 # 28 [c=4 l=4] *rs6000.md:12311
lbzx 8,5,9 # 31 [c=8 l=4] zero_extendqisi2/0
lbzx 11,4,9 # 32 [c=8 l=4] zero_extendqisi2/0
rldicl 10,0,0,32 # 54 [c=4 l=4] zero_extendsidi2/1
cmpw 7,8,11 # 33 [c=4 l=4] *cmpsi_signed
bne 7,.L3 # 34 [c=4 l=4] *rs6000.md:12311
rldicl 9,7,0,32 # 37 [c=4 l=4] zero_extendsidi2/1
beq 6,.L3 # 39 [c=4 l=4] *rs6000.md:12311
lbzx 8,5,9 # 42 [c=8 l=4] zero_extendqisi2/0
lbzx 7,4,9 # 43 [c=8 l=4] zero_extendqisi2/0
cmpw 7,8,7 # 44 [c=4 l=4] *cmpsi_signed
bne 7,.L3 # 45 [c=4 l=4] *rs6000.md:12311
beq 1,.L7 # 50 [c=4 l=4] *rs6000.md:12311
lbzx 9,5,6 # 55 [c=8 l=4] zero_extendqisi2/0
lbzx 8,4,6 # 56 [c=8 l=4] zero_extendqisi2/0
cmpw 7,9,8 # 57 [c=4 l=4] *cmpsi_signed
bne 7,.L7 # 58 [c=4 l=4] *rs6000.md:12311
.L2:
cmplw 7,3,10 # 62 [c=4 l=4] *cmpsi_unsigned
addi 9,6,2 # 25 [c=4 l=4] *addsi3/1
addi 7,6,3 # 36 [c=4 l=4] *addsi3/1
addi 6,6,4 # 47 [c=4 l=4] *addsi3/1
cmplw 5,3,9 # 27 [c=4 l=4] *cmpsi_unsigned
cmplw 1,3,6 # 49 [c=4 l=4] *cmpsi_unsigned
cmplw 6,3,7 # 38 [c=4 l=4] *cmpsi_unsigned
addi 0,10,4 # 53 [c=4 l=4] *addsi3/1
rldicl 9,9,0,32 # 26 [c=4 l=4] zero_extendsidi2/1
rldicl 6,6,0,32 # 48 [c=4 l=4] zero_extendsidi2/1
bne 7,.L4 # 63 [c=4 l=4] *rs6000.md:12311
mr 9,3 # 10 [c=4 l=4] *movdi_internal64/2
.L3:
extsw 3,9 # 71 [c=4 l=4] extendsidi2/1
blr # 105 [c=4 l=4] simple_return
.p2align 4,,15
.L7:
mr 9,6 # 9 [c=4 l=4] *movdi_internal64/2
extsw 3,9 # 113 [c=4 l=4] extendsidi2/1
blr # 116 [c=4 l=4] simple_return
.p2align 4,,15
.L5:
mr 9,10 # 8 [c=4 l=4] *movdi_internal64/2
extsw 3,9 # 121 [c=4 l=4] extendsidi2/1
blr # 124 [c=4 l=4] simple_return
.long 0
.byte 0,0,0,0,0,0,0,0
.cfi_endproc
.LFE22:
.size bt_skip_func,.-bt_skip_func
.section ".toc","aw"
.align 3
.LC1:
.quad .LC0+3
.section .text.startup,"ax",@progbits
.align 2
.p2align 4,,15
.globl main
.type main, @function
main:
.LFB23:
.cfi_startproc
.LCF1:
0: addis 2,12,.TOC.-.LCF1@ha
addi 2,2,.TOC.-.LCF1@l
.localentry main,.-main
mflr 0 # 23 [c=4 l=4] *movdi_internal64/21
addis 4,2,.LC1@toc@ha # 35 [c=12 l=8] fusion_gpr_load_di
ld 4,.LC1@toc@l(4)
li 6,1 # 8 [c=4 l=4] *movdi_internal64/3
li 5,3 # 9 [c=4 l=4] *movdi_internal64/3
li 3,55 # 11 [c=4 l=4] *movdi_internal64/3
std 0,16(1) # 24 [c=4 l=4] *movdi_internal64/0
stdu 1,-32(1) # 25 [c=4 l=4] movdi_di_update/1
.cfi_def_cfa_offset 32
.cfi_offset 65, 16
bl bt_skip_func # 12 [c=4 l=4] *call_value_local_aixdi
addi 1,1,32 # 28 [c=4 l=4] *adddi3/1
.cfi_def_cfa_offset 0
li 3,0 # 17 [c=4 l=4] *movdi_internal64/3
ld 0,16(1) # 29 [c=8 l=4] *movdi_internal64/1
mtlr 0 # 30 [c=4 l=4] *movdi_internal64/22
.cfi_restore 65
blr # 31 [c=4 l=4] simple_return
.long 0
.byte 0,0,0,1,128,0,0,0
.cfi_endproc
.LFE23:
.size main,.-main
.section .rodata.str1.8,"aMS",@progbits,1
.align 3
.LC0:
.string "ttttttttttttttttthis is some text that should be longer"
.ident "GCC: (GNU) 9.0.0 20180716 (experimental)"
.section .note.GNU-stack,"",@progbits
[-- Attachment #7: ivsimple.c --]
[-- Type: text/plain, Size: 802 bytes --]
#include <stdlib.h>
#include <string.h>
int
bt_skip_func(const __uint32_t len_limit, const __uint8_t *cur,
int delta, __uint32_t len) {
const __uint8_t *pb = cur - delta;
while (++len != len_limit) {
if (pb[len] != cur[len])
break;
if (++len == len_limit)
break;
if (pb[len] != cur[len])
break;
if (++len == len_limit)
break;
if (pb[len] != cur[len])
break;
if (++len == len_limit)
break;
if (pb[len] != cur[len])
break;
}
return len;
}
int main (int argc, char *argv[]) {
char *text_input = "ttttttttttttttttthis is some text that should be longer";
int len_limit = strlen (text_input);
int pos = 0;
int cur_match = 0;
int depth = 0;
int result = bt_skip_func(len_limit, text_input + 3, 3, 1);
}
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [RFC] Induction variable candidates not sufficiently general
2018-07-16 18:09 ` Kelvin Nilsen
@ 2018-07-21 1:28 ` Bin.Cheng
2018-07-23 9:54 ` Richard Biener
0 siblings, 1 reply; 6+ messages in thread
From: Bin.Cheng @ 2018-07-21 1:28 UTC (permalink / raw)
To: Kelvin Nilsen; +Cc: gcc-patches List
On Tue, Jul 17, 2018 at 2:08 AM, Kelvin Nilsen <kdnilsen@linux.ibm.com> wrote:
> Thanks for looking at this for me. In simplifying the test case for a bug report, I've narrowed the "problem" to integer overflow considerations. My len variable is declared int, and the target has 64-bit pointers. I'm gathering that the "manual transformation" I quoted below is not considered "equivalent" to the original source code due to different integer overflow behaviors. If I redeclare len to be unsigned long long, then I automatically get the optimizations that I was originally expecting.
>
> I suppose this is really NOT a bug?
As your test case demonstrates, it is caused by wrapping unsigned int32.
>
> Is there a compiler optimization flag that allows the optimizer to ignore array index integer overflow in considering legal optimizations?
I am not aware of one for unsigned integer, and I guess it won't be
introduced in the future either?
Thanks,
bin
>
>
>
> On 7/13/18 9:14 PM, Bin.Cheng wrote:
>> On Fri, Jul 13, 2018 at 6:04 AM, Kelvin Nilsen <kdnilsen@linux.ibm.com> wrote:
>>> A somewhat old "issue report" pointed me to the code generated for a 4-fold manually unrolled version of the following loop:
>>>
>>>> while (++len != len_limit) /* this is loop */
>>>> if (pb[len] != cur[len])
>>>> break;
>>>
>>> As unrolled, the loop appears as:
>>>
>>>> while (++len != len_limit) /* this is loop */ {
>>>> if (pb[len] != cur[len])
>>>> break;
>>>> if (++len == len_limit) /* unrolled 2nd iteration */
>>>> break;
>>>> if (pb[len] != cur[len])
>>>> break;
>>>> if (++len == len_limit) /* unrolled 3rd iteration */
>>>> break;
>>>> if (pb[len] != cur[len])
>>>> break;
>>>> if (++len == len_limit) /* unrolled 4th iteration */
>>>> break;
>>>> if (pb[len] != cur[len])
>>>> break;
>>>> }
>>>
>>> In examining the behavior of tree-ssa-loop-ivopts.c, I've discovered the only induction variable candidates that are being considered are all forms of the len variable. We are not considering any induction variables to represent the address expressions &pb[len] and &cur[len].
>>>
>>> I rewrote the source code for this loop to make the addressing expressions more explicit, as in the following:
>>>
>>>> cur++;
>>>> while (++pb != last_pb) /* this is loop */ {
>>>> if (*pb != *cur)
>>>> break;
>>>> ++cur;
>>>> if (++pb == last_pb) /* unrolled 2nd iteration */
>>>> break;
>>>> if (*pb != *cur)
>>>> break;
>>>> ++cur;
>>>> if (++pb == last_pb) /* unrolled 3rd iteration */
>>>> break;
>>>> if (*pb != *cur)
>>>> break;
>>>> ++cur;
>>>> if (++pb == last_pb) /* unrolled 4th iteration */
>>>> break;
>>>> if (*pb != *cur)
>>>> break;
>>>> ++cur;
>>>> }
>>>
>>> Now, gcc does a better job of identifying the "address expression induction variables". This version of the loop runs about 10% faster than the original on my target architecture.
>>>
>>> This would seem to be a textbook pattern for the induction variable analysis. Does anyone have any thoughts on the best way to add these candidates to the set of induction variables that are considered by tree-ssa-loop-ivopts.c?
>>>
>>> Thanks in advance for any suggestions.
>>>
>> Hi,
>> Could you please file a bug with your original slow test code
>> attached? I tried to construct meaningful test case from your code
>> snippet but not successful. There is difference in generated
>> assembly, but it's not that fundamental. So a bug with preprocessed
>> test would be high appreciated.
>> I think there are two potential issues in cost computation for such
>> case: invariant expression and iv uses outside of loop handled as
>> inside uses.
>>
>> Thanks,
>> bin
>>
>>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [RFC] Induction variable candidates not sufficiently general
2018-07-21 1:28 ` Bin.Cheng
@ 2018-07-23 9:54 ` Richard Biener
0 siblings, 0 replies; 6+ messages in thread
From: Richard Biener @ 2018-07-23 9:54 UTC (permalink / raw)
To: Amker.Cheng; +Cc: kdnilsen, GCC Patches
On Sat, Jul 21, 2018 at 3:28 AM Bin.Cheng <amker.cheng@gmail.com> wrote:
>
> On Tue, Jul 17, 2018 at 2:08 AM, Kelvin Nilsen <kdnilsen@linux.ibm.com> wrote:
> > Thanks for looking at this for me. In simplifying the test case for a bug report, I've narrowed the "problem" to integer overflow considerations. My len variable is declared int, and the target has 64-bit pointers. I'm gathering that the "manual transformation" I quoted below is not considered "equivalent" to the original source code due to different integer overflow behaviors. If I redeclare len to be unsigned long long, then I automatically get the optimizations that I was originally expecting.
> >
> > I suppose this is really NOT a bug?
> As your test case demonstrates, it is caused by wrapping unsigned int32.
> >
> > Is there a compiler optimization flag that allows the optimizer to ignore array index integer overflow in considering legal optimizations?
> I am not aware of one for unsigned integer, and I guess it won't be
> introduced in the future either?
We've had -funsafe-loop-optimizations in the past but that only
concerned niter analysis, not scalar evolution analysis
which is likely required here.
And no, there's no plan to re-introduce those.
Richard.
> Thanks,
> bin
> >
> >
> >
> > On 7/13/18 9:14 PM, Bin.Cheng wrote:
> >> On Fri, Jul 13, 2018 at 6:04 AM, Kelvin Nilsen <kdnilsen@linux.ibm.com> wrote:
> >>> A somewhat old "issue report" pointed me to the code generated for a 4-fold manually unrolled version of the following loop:
> >>>
> >>>> while (++len != len_limit) /* this is loop */
> >>>> if (pb[len] != cur[len])
> >>>> break;
> >>>
> >>> As unrolled, the loop appears as:
> >>>
> >>>> while (++len != len_limit) /* this is loop */ {
> >>>> if (pb[len] != cur[len])
> >>>> break;
> >>>> if (++len == len_limit) /* unrolled 2nd iteration */
> >>>> break;
> >>>> if (pb[len] != cur[len])
> >>>> break;
> >>>> if (++len == len_limit) /* unrolled 3rd iteration */
> >>>> break;
> >>>> if (pb[len] != cur[len])
> >>>> break;
> >>>> if (++len == len_limit) /* unrolled 4th iteration */
> >>>> break;
> >>>> if (pb[len] != cur[len])
> >>>> break;
> >>>> }
> >>>
> >>> In examining the behavior of tree-ssa-loop-ivopts.c, I've discovered the only induction variable candidates that are being considered are all forms of the len variable. We are not considering any induction variables to represent the address expressions &pb[len] and &cur[len].
> >>>
> >>> I rewrote the source code for this loop to make the addressing expressions more explicit, as in the following:
> >>>
> >>>> cur++;
> >>>> while (++pb != last_pb) /* this is loop */ {
> >>>> if (*pb != *cur)
> >>>> break;
> >>>> ++cur;
> >>>> if (++pb == last_pb) /* unrolled 2nd iteration */
> >>>> break;
> >>>> if (*pb != *cur)
> >>>> break;
> >>>> ++cur;
> >>>> if (++pb == last_pb) /* unrolled 3rd iteration */
> >>>> break;
> >>>> if (*pb != *cur)
> >>>> break;
> >>>> ++cur;
> >>>> if (++pb == last_pb) /* unrolled 4th iteration */
> >>>> break;
> >>>> if (*pb != *cur)
> >>>> break;
> >>>> ++cur;
> >>>> }
> >>>
> >>> Now, gcc does a better job of identifying the "address expression induction variables". This version of the loop runs about 10% faster than the original on my target architecture.
> >>>
> >>> This would seem to be a textbook pattern for the induction variable analysis. Does anyone have any thoughts on the best way to add these candidates to the set of induction variables that are considered by tree-ssa-loop-ivopts.c?
> >>>
> >>> Thanks in advance for any suggestions.
> >>>
> >> Hi,
> >> Could you please file a bug with your original slow test code
> >> attached? I tried to construct meaningful test case from your code
> >> snippet but not successful. There is difference in generated
> >> assembly, but it's not that fundamental. So a bug with preprocessed
> >> test would be high appreciated.
> >> I think there are two potential issues in cost computation for such
> >> case: invariant expression and iv uses outside of loop handled as
> >> inside uses.
> >>
> >> Thanks,
> >> bin
> >>
> >>
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2018-07-23 9:54 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-07-12 22:05 [RFC] Induction variable candidates not sufficiently general Kelvin Nilsen
2018-07-13 6:50 ` Richard Biener
2018-07-14 2:14 ` Bin.Cheng
2018-07-16 18:09 ` Kelvin Nilsen
2018-07-21 1:28 ` Bin.Cheng
2018-07-23 9:54 ` Richard Biener
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