* [ISSUE] [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write
@ 2023-10-26 6:18 riddicc
2023-10-26 10:48 ` [ISSUE] [CLOSED] " ahesford
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: riddicc @ 2023-10-26 6:18 UTC (permalink / raw)
To: ml
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New issue by riddicc on void-packages repository
https://github.com/void-linux/void-packages/issues/46899
Description:
### Is this a new report?
Yes
### System Info
Void 6.5.5_2 x86_64 GenuineIntel uptodate hold rrrmFFF
### Package(s) Affected
cross-arm-none-eabi-gcc-9.3.0_1
### Does a report exist for this bug with the project's home (upstream) and/or another distro?
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111582
somehow my related issue #46239 gets no attention... dunno why... am i doing something wrong?
### Expected behaviour
the code should be easier/faster to execute...
there are possibly much more issues, that could be fixed in the current version 13.2.0 of gcc...
### Actual behaviour
it adds instructions like this:
```
sub sp, sp, #16
mov r2, sp
add sp, sp, #16
```
without ever using something on the stack...
### Steps to reproduce
1. install cross-arm-none-eabi-gcc
2. compile source code containing bitfield operations [[1]]
3. u will get [2]
[[1]]: source:
```
# 1 "a.c"
# 1 "/tmp//"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "a.c"
typedef unsigned char u8;
typedef unsigned int u32;
extern int fatal();
__attribute__((always_inline)) inline u32 lsb(const u8 l) { return (1U<<l)-1U; }
typedef struct { u32 a; u32 msk; u32 v; u8 rs:1; u8 aw:7; } Reg;
__attribute__((always_inline)) inline Reg GI(u32 A, u32 N, u32 RS, u8 AW) { Reg R={A+4*N,lsb(32),0,RS?1:0,AW}; return R; }
__attribute__((always_inline)) inline u32 GS(Reg R) {
for (u32 i=0, msk=lsb(8); R.aw==1 && msk; i++, msk<<=8)
if ( !~(R.msk | msk) ) {
const u8 v = R.v >> (i*8);
if (R.rs || msk==~R.msk) return (((volatile u8*)R.a)[i] = v) << (i*8);
else if (R.v==~R.msk) return (((volatile u8*)R.a)[i] |= v) << (i*8);
return (((volatile u8*)R.a)[i] = (((volatile u8*)R.a)[i] & (R.msk>>(i*8))) | v) << (i*8);
}
return 0;
}
__attribute__((always_inline)) inline Reg GU(Reg R, u32 A, u32 N, u8 o, u8 w, u32 v) {
const u32 msk=~(lsb(w)<<o); R.msk&=msk; R.v&=msk;
R.v |= (v<<o);
return R;
}
u32 artiSP() { return GS(GU(GI(0xE0000000,42,0,1),0xE0000000,42,17,3,2)); }
```
[2]: resulting assembly code:
```
artiSP:
sub sp, sp, #16
mov r2, sp
movs r3, #2
strb r3, [r2, #12]
...
add sp, sp, #16
bx lr
```
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write
2023-10-26 6:18 [ISSUE] [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write riddicc
2023-10-26 10:48 ` [ISSUE] [CLOSED] " ahesford
@ 2023-10-26 10:48 ` ahesford
2023-10-26 15:27 ` riddicc
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: ahesford @ 2023-10-26 10:48 UTC (permalink / raw)
To: ml
[-- Attachment #1: Type: text/plain, Size: 321 bytes --]
New comment by ahesford on void-packages repository
https://github.com/void-linux/void-packages/issues/46899#issuecomment-1780875454
Comment:
This is not a Void bug. The software is executing as implemented. If you want the better performance offered by a newer version, either await the update or attempt it yourself.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [ISSUE] [CLOSED] [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write
2023-10-26 6:18 [ISSUE] [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write riddicc
@ 2023-10-26 10:48 ` ahesford
2023-10-26 10:48 ` ahesford
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: ahesford @ 2023-10-26 10:48 UTC (permalink / raw)
To: ml
[-- Attachment #1: Type: text/plain, Size: 2401 bytes --]
Closed issue by riddicc on void-packages repository
https://github.com/void-linux/void-packages/issues/46899
Description:
### Is this a new report?
Yes
### System Info
Void 6.5.5_2 x86_64 GenuineIntel uptodate hold rrrmFFF
### Package(s) Affected
cross-arm-none-eabi-gcc-9.3.0_1
### Does a report exist for this bug with the project's home (upstream) and/or another distro?
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111582
somehow my related issue #46239 gets no attention... dunno why... am i doing something wrong?
### Expected behaviour
the code should be easier/faster to execute...
there are possibly much more issues, that could be fixed in the current version 13.2.0 of gcc...
### Actual behaviour
it adds instructions like this:
```
sub sp, sp, #16
mov r2, sp
add sp, sp, #16
```
without ever using something on the stack...
### Steps to reproduce
1. install cross-arm-none-eabi-gcc
2. compile source code containing bitfield operations [[1]]
3. u will get [2]
[[1]]: source:
```
# 1 "a.c"
# 1 "/tmp//"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "a.c"
typedef unsigned char u8;
typedef unsigned int u32;
extern int fatal();
__attribute__((always_inline)) inline u32 lsb(const u8 l) { return (1U<<l)-1U; }
typedef struct { u32 a; u32 msk; u32 v; u8 rs:1; u8 aw:7; } Reg;
__attribute__((always_inline)) inline Reg GI(u32 A, u32 N, u32 RS, u8 AW) { Reg R={A+4*N,lsb(32),0,RS?1:0,AW}; return R; }
__attribute__((always_inline)) inline u32 GS(Reg R) {
for (u32 i=0, msk=lsb(8); R.aw==1 && msk; i++, msk<<=8)
if ( !~(R.msk | msk) ) {
const u8 v = R.v >> (i*8);
if (R.rs || msk==~R.msk) return (((volatile u8*)R.a)[i] = v) << (i*8);
else if (R.v==~R.msk) return (((volatile u8*)R.a)[i] |= v) << (i*8);
return (((volatile u8*)R.a)[i] = (((volatile u8*)R.a)[i] & (R.msk>>(i*8))) | v) << (i*8);
}
return 0;
}
__attribute__((always_inline)) inline Reg GU(Reg R, u32 A, u32 N, u8 o, u8 w, u32 v) {
const u32 msk=~(lsb(w)<<o); R.msk&=msk; R.v&=msk;
R.v |= (v<<o);
return R;
}
u32 artiSP() { return GS(GU(GI(0xE0000000,42,0,1),0xE0000000,42,17,3,2)); }
```
[2]: resulting assembly code:
```
artiSP:
sub sp, sp, #16
mov r2, sp
movs r3, #2
strb r3, [r2, #12]
...
add sp, sp, #16
bx lr
```
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write
2023-10-26 6:18 [ISSUE] [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write riddicc
2023-10-26 10:48 ` [ISSUE] [CLOSED] " ahesford
2023-10-26 10:48 ` ahesford
@ 2023-10-26 15:27 ` riddicc
2023-10-26 15:28 ` riddicc
2023-10-26 15:30 ` ahesford
4 siblings, 0 replies; 6+ messages in thread
From: riddicc @ 2023-10-26 15:27 UTC (permalink / raw)
To: ml
[-- Attachment #1: Type: text/plain, Size: 277 bytes --]
New comment by riddicc on void-packages repository
https://github.com/void-linux/void-packages/issues/46899#issuecomment-1781354750
Comment:
> await the update
how long will it take?
> attempt it yourself
how can i become the maintainer in order to attempt it myself?
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write
2023-10-26 6:18 [ISSUE] [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write riddicc
` (2 preceding siblings ...)
2023-10-26 15:27 ` riddicc
@ 2023-10-26 15:28 ` riddicc
2023-10-26 15:30 ` ahesford
4 siblings, 0 replies; 6+ messages in thread
From: riddicc @ 2023-10-26 15:28 UTC (permalink / raw)
To: ml
[-- Attachment #1: Type: text/plain, Size: 281 bytes --]
New comment by riddicc on void-packages repository
https://github.com/void-linux/void-packages/issues/46899#issuecomment-1781354750
Comment:
> await the update
how long will it take?
> attempt it yourself
how can i become the maintainer in order to attempt it myself?
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write
2023-10-26 6:18 [ISSUE] [cross-arm-none-eabi-gcc] / suboptimal optimization: superfluous stack write riddicc
` (3 preceding siblings ...)
2023-10-26 15:28 ` riddicc
@ 2023-10-26 15:30 ` ahesford
4 siblings, 0 replies; 6+ messages in thread
From: ahesford @ 2023-10-26 15:30 UTC (permalink / raw)
To: ml
[-- Attachment #1: Type: text/plain, Size: 505 bytes --]
New comment by ahesford on void-packages repository
https://github.com/void-linux/void-packages/issues/46899#issuecomment-1781360137
Comment:
It takes how ever long it takes. We're a volunteer organization, and people work on what they want, when they want.
You don't need to become a maintainer to contribute updates to packages. See the [contributing guide](https://github.com/void-linux/void-packages/blob/master/CONTRIBUTING.md) for information on how to submit pull requests to update packages.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2023-10-26 10:48 ` [ISSUE] [CLOSED] " ahesford
2023-10-26 10:48 ` ahesford
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