[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170
--- Comment #22 from CVS Commits ---
The releases/gcc-12 branch has been updated by hongtao Liu
:
https://gcc.gnu.org/g:1e36498710f9ca84fefa578863cf505f484601b1
commit r12-9944-g1e36498710f9ca84fefa578863cf505f484601b1
Author: liuhongt
Date: Wed Jul 5 13:45:11 2023 +0800
Disparage slightly for the alternative which move DFmode between SSE_REGS
and GENERAL_REGS.
For testcase
void __cond_swap(double* __x, double* __y) {
bool __r = (*__x < *__y);
auto __tmp = __r ? *__x : *__y;
*__y = __r ? *__y : *__x;
*__x = __tmp;
}
GCC-14 with -O2 and -march=x86-64 options generates the following code:
__cond_swap(double*, double*):
movsd xmm1, QWORD PTR [rdi]
movsd xmm0, QWORD PTR [rsi]
comisd xmm0, xmm1
jbe .L2
movqrax, xmm1
movapd xmm1, xmm0
movqxmm0, rax
.L2:
movsd QWORD PTR [rsi], xmm1
movsd QWORD PTR [rdi], xmm0
ret
rax is used to save and restore DFmode value. In RA both GENERAL_REGS
and SSE_REGS cost zero since we didn't disparage the
alternative in movdf_internal pattern, according to register
allocation order, GENERAL_REGS is allocated. The patch add ? for
alternative (r,v) and (v,r) just like we did for movsf/hf/bf_internal
pattern, after that we get optimal RA.
__cond_swap:
.LFB0:
.cfi_startproc
movsd (%rdi), %xmm1
movsd (%rsi), %xmm0
comisd %xmm1, %xmm0
jbe .L2
movapd %xmm1, %xmm2
movapd %xmm0, %xmm1
movapd %xmm2, %xmm0
.L2:
movsd %xmm1, (%rsi)
movsd %xmm0, (%rdi)
ret
gcc/ChangeLog:
PR target/110170
* config/i386/i386.md (movdf_internal): Disparage slightly for
2 alternatives (r,v) and (v,r) by adding constraint modifier
'?'.
gcc/testsuite/ChangeLog:
* gcc.target/i386/pr110170-3.c: New test.
(cherry picked from commit 37a231cc7594d12ba0822077018aad751a6fb94e)
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170
--- Comment #21 from CVS Commits ---
The releases/gcc-11 branch has been updated by hongtao Liu
:
https://gcc.gnu.org/g:0d005deb6c8a956b4f7ccb6e70e8e7830a40fed9
commit r11-11065-g0d005deb6c8a956b4f7ccb6e70e8e7830a40fed9
Author: liuhongt
Date: Wed Jul 5 13:45:11 2023 +0800
Disparage slightly for the alternative which move DFmode between SSE_REGS
and GENERAL_REGS.
For testcase
void __cond_swap(double* __x, double* __y) {
bool __r = (*__x < *__y);
auto __tmp = __r ? *__x : *__y;
*__y = __r ? *__y : *__x;
*__x = __tmp;
}
GCC-14 with -O2 and -march=x86-64 options generates the following code:
__cond_swap(double*, double*):
movsd xmm1, QWORD PTR [rdi]
movsd xmm0, QWORD PTR [rsi]
comisd xmm0, xmm1
jbe .L2
movqrax, xmm1
movapd xmm1, xmm0
movqxmm0, rax
.L2:
movsd QWORD PTR [rsi], xmm1
movsd QWORD PTR [rdi], xmm0
ret
rax is used to save and restore DFmode value. In RA both GENERAL_REGS
and SSE_REGS cost zero since we didn't disparage the
alternative in movdf_internal pattern, according to register
allocation order, GENERAL_REGS is allocated. The patch add ? for
alternative (r,v) and (v,r) just like we did for movsf/hf/bf_internal
pattern, after that we get optimal RA.
__cond_swap:
.LFB0:
.cfi_startproc
movsd (%rdi), %xmm1
movsd (%rsi), %xmm0
comisd %xmm1, %xmm0
jbe .L2
movapd %xmm1, %xmm2
movapd %xmm0, %xmm1
movapd %xmm2, %xmm0
.L2:
movsd %xmm1, (%rsi)
movsd %xmm0, (%rdi)
ret
gcc/ChangeLog:
PR target/110170
* config/i386/i386.md (movdf_internal): Disparage slightly for
2 alternatives (r,v) and (v,r) by adding constraint modifier
'?'.
gcc/testsuite/ChangeLog:
* gcc.target/i386/pr110170-3.c: New test.
(cherry picked from commit 37a231cc7594d12ba0822077018aad751a6fb94e)
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170
--- Comment #20 from CVS Commits ---
The releases/gcc-13 branch has been updated by hongtao Liu
:
https://gcc.gnu.org/g:27165633859bdf92589428213edfeccdb49b7d83
commit r13-7956-g27165633859bdf92589428213edfeccdb49b7d83
Author: liuhongt
Date: Wed Jul 5 13:45:11 2023 +0800
Disparage slightly for the alternative which move DFmode between SSE_REGS
and GENERAL_REGS.
For testcase
void __cond_swap(double* __x, double* __y) {
bool __r = (*__x < *__y);
auto __tmp = __r ? *__x : *__y;
*__y = __r ? *__y : *__x;
*__x = __tmp;
}
GCC-14 with -O2 and -march=x86-64 options generates the following code:
__cond_swap(double*, double*):
movsd xmm1, QWORD PTR [rdi]
movsd xmm0, QWORD PTR [rsi]
comisd xmm0, xmm1
jbe .L2
movqrax, xmm1
movapd xmm1, xmm0
movqxmm0, rax
.L2:
movsd QWORD PTR [rsi], xmm1
movsd QWORD PTR [rdi], xmm0
ret
rax is used to save and restore DFmode value. In RA both GENERAL_REGS
and SSE_REGS cost zero since we didn't disparage the
alternative in movdf_internal pattern, according to register
allocation order, GENERAL_REGS is allocated. The patch add ? for
alternative (r,v) and (v,r) just like we did for movsf/hf/bf_internal
pattern, after that we get optimal RA.
__cond_swap:
.LFB0:
.cfi_startproc
movsd (%rdi), %xmm1
movsd (%rsi), %xmm0
comisd %xmm1, %xmm0
jbe .L2
movapd %xmm1, %xmm2
movapd %xmm0, %xmm1
movapd %xmm2, %xmm0
.L2:
movsd %xmm1, (%rsi)
movsd %xmm0, (%rdi)
ret
gcc/ChangeLog:
PR target/110170
* config/i386/i386.md (movdf_internal): Disparage slightly for
2 alternatives (r,v) and (v,r) by adding constraint modifier
'?'.
gcc/testsuite/ChangeLog:
* gcc.target/i386/pr110170-3.c: New test.
(cherry picked from commit 37a231cc7594d12ba0822077018aad751a6fb94e)
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 Richard Biener changed: What|Removed |Added Resolution|--- |FIXED Status|REOPENED|RESOLVED --- Comment #19 from Richard Biener --- Fixed now.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 Richard Biener changed: What|Removed |Added Target Milestone|14.0|--- Resolution|FIXED |--- Status|RESOLVED|REOPENED --- Comment #18 from Richard Biener --- Huh, right. Somehow I thought minss/maxss is SSE 4.1. I do have a patch series that fixes this, the PR88540 is missing for this but it has some fallout still.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 --- Comment #17 from Hongtao.liu --- (In reply to Richard Biener from comment #16) > This is fixed now. The original issue is for sse2, my patch only fixed misoptimization for sse4.1.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 Richard Biener changed: What|Removed |Added Status|NEW |RESOLVED Target Milestone|--- |14.0 Resolution|--- |FIXED --- Comment #16 from Richard Biener --- This is fixed now.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 --- Comment #15 from CVS Commits --- The master branch has been updated by hongtao Liu : https://gcc.gnu.org/g:e5c64efb1367459dbc2d2e29856f23908cb503c1 commit r14-2432-ge5c64efb1367459dbc2d2e29856f23908cb503c1 Author: liuhongt Date: Tue Jul 11 21:21:03 2023 +0800 Fix typo in the testcase. Antony Polukhin 2023-07-11 09:51:58 UTC There's a typo at https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/testsuite/g%2B%2B.target/i386/pr110170.C;h=e638b12a5ee2264ecef77acca86432a9f24b103b;hb=d41a57c46df6f8f7dae0c0a8b349e734806a837b#l87 It should be `|| !test3() || !test3r()` rather than `|| !test3() || !test4r()` gcc/testsuite/ChangeLog: PR target/110170 * g++.target/i386/pr110170.C: Fix typo.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 --- Comment #14 from Hongtao.liu --- (In reply to Antony Polukhin from comment #13) > There's a typo at > https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/testsuite/g%2B%2B.target/ > i386/pr110170.C;h=e638b12a5ee2264ecef77acca86432a9f24b103b; > hb=d41a57c46df6f8f7dae0c0a8b349e734806a837b#l87 > > It should be `|| !test3() || !test3r()` rather than `|| !test3() || > !test4r()` Yes, thanks for the reminder.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 --- Comment #13 from Antony Polukhin --- There's a typo at https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/testsuite/g%2B%2B.target/i386/pr110170.C;h=e638b12a5ee2264ecef77acca86432a9f24b103b;hb=d41a57c46df6f8f7dae0c0a8b349e734806a837b#l87 It should be `|| !test3() || !test3r()` rather than `|| !test3() || !test4r()`
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 --- Comment #12 from CVS Commits --- The master branch has been updated by hongtao Liu : https://gcc.gnu.org/g:d41a57c46df6f8f7dae0c0a8b349e734806a837b commit r14-2403-gd41a57c46df6f8f7dae0c0a8b349e734806a837b Author: liuhongt Date: Mon Jul 3 18:19:19 2023 +0800 Add pre_reload splitter to detect fp min/max pattern. We have ix86_expand_sse_fp_minmax to detect min/max sematics, but it requires rtx_equal_p for cmp_op0/cmp_op1 and if_true/if_false, for the testcase in the PR, there's an extra move from cmp_op0 to if_true, and it failed ix86_expand_sse_fp_minmax. This patch adds pre_reload splitter to detect the min/max pattern. Operands order in MINSS matters for signed zero and NANs, since the instruction always returns second operand when any operand is NAN or both operands are zero. gcc/ChangeLog: PR target/110170 * config/i386/i386.md (*ieee_max3_1): New pre_reload splitter to detect fp max pattern. (*ieee_min3_1): Ditto, but for fp min pattern. gcc/testsuite/ChangeLog: * g++.target/i386/pr110170.C: New test. * gcc.target/i386/pr110170.c: New test.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170
--- Comment #11 from CVS Commits ---
The master branch has been updated by hongtao Liu :
https://gcc.gnu.org/g:37a231cc7594d12ba0822077018aad751a6fb94e
commit r14-2337-g37a231cc7594d12ba0822077018aad751a6fb94e
Author: liuhongt
Date: Wed Jul 5 13:45:11 2023 +0800
Disparage slightly for the alternative which move DFmode between SSE_REGS
and GENERAL_REGS.
For testcase
void __cond_swap(double* __x, double* __y) {
bool __r = (*__x < *__y);
auto __tmp = __r ? *__x : *__y;
*__y = __r ? *__y : *__x;
*__x = __tmp;
}
GCC-14 with -O2 and -march=x86-64 options generates the following code:
__cond_swap(double*, double*):
movsd xmm1, QWORD PTR [rdi]
movsd xmm0, QWORD PTR [rsi]
comisd xmm0, xmm1
jbe .L2
movqrax, xmm1
movapd xmm1, xmm0
movqxmm0, rax
.L2:
movsd QWORD PTR [rsi], xmm1
movsd QWORD PTR [rdi], xmm0
ret
rax is used to save and restore DFmode value. In RA both GENERAL_REGS
and SSE_REGS cost zero since we didn't disparage the
alternative in movdf_internal pattern, according to register
allocation order, GENERAL_REGS is allocated. The patch add ? for
alternative (r,v) and (v,r) just like we did for movsf/hf/bf_internal
pattern, after that we get optimal RA.
__cond_swap:
.LFB0:
.cfi_startproc
movsd (%rdi), %xmm1
movsd (%rsi), %xmm0
comisd %xmm1, %xmm0
jbe .L2
movapd %xmm1, %xmm2
movapd %xmm0, %xmm1
movapd %xmm2, %xmm0
.L2:
movsd %xmm1, (%rsi)
movsd %xmm0, (%rdi)
ret
gcc/ChangeLog:
PR target/110170
* config/i386/i386.md (movdf_internal): Disparage slightly for
2 alternatives (r,v) and (v,r) by adding constraint modifier
'?'.
gcc/testsuite/ChangeLog:
* gcc.target/i386/pr110170-3.c: New test.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170
--- Comment #10 from Hongtao.liu ---
There're couple of other issues.
1. rtx_cost for and/ior/xor:SF/DF is not right, it actually generate vector
instructions.
2. branch_cost is COSTS_N_INSN(1) instead of BRANCH_COST ().
which make noce more conservative to eliminate condition.
w/ sse2, backend tries
(insn 34 0 36 (set (reg:DF 86 [ _1 ])
(reg:DF 82 [ _1 ])) 151 {*movdf_internal}
(nil))
(insn 36 34 37 (set (reg:DF 92)
(unspec:DF [
(reg:DF 83 [ _2 ])
(reg:DF 82 [ _1 ])
] UNSPEC_IEEE_MAX)) -1
(nil))
(insn 37 36 38 (set (reg:DF 93)
(lt:DF (reg:DF 82 [ _1 ])
(reg:DF 83 [ _2 ]))) -1
(nil))
(insn 38 37 39 (set (reg:DF 94)
(and:DF (reg:DF 86 [ _1 ])
(reg:DF 93))) -1
(nil))
(insn 39 38 40 (set (reg:DF 95)
(and:DF (not:DF (reg:DF 93))
(reg:DF 83 [ _2 ]))) -1
(nil))
(insn 40 39 41 (set (reg:DF 83 [ _2 ])
(ior:DF (reg:DF 95)
(reg:DF 94))) -1
(nil))
(insn 41 40 0 (set (reg:DF 82 [ _1 ])
(reg:DF 92)) 151 {*movdf_internal}
(nil))
which is cost is 28, and original cost is 12 (3 moves + 1 branch).(needs also
conside comparison? since it's counted in cmov seq), if use ix86_branch_cost +
count comparison cost in the orginal seq, then the cost should be 28 vs 28.)
(insn 5 17 6 3 (set (reg:DF 86 [ _1 ])
(reg:DF 82 [ _1 ]))
"/export/users/liuhongt/tools-build/build_intel-innersource_pr110170_debug/test.c":5:23
151 {*movdf_internal}
(expr_list:REG_DEAD (reg:DF 82 [ _1 ])
(nil)))
(insn 6 5 7 3 (set (reg:DF 82 [ _1 ])
(reg:DF 83 [ _2 ]))
"/export/users/liuhongt/tools-build/build_intel-innersource_pr110170_debug/test.c":6:15
discrim 1 151 {*movdf_internal}
(expr_list:REG_DEAD (reg:DF 83 [ _2 ])
(nil)))
(insn 7 6 18 3 (set (reg:DF 83 [ _2 ])
(reg:DF 86 [ _1 ]))
"/export/users/liuhongt/tools-build/build_intel-innersource_pr110170_debug/test.c":5:23
discrim 1 151 {*movdf_internal}
(expr_list:REG_DEAD (reg:DF 86 [ _1 ])
(nil)))
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 --- Comment #9 from Hongtao.liu --- (In reply to Hongtao.liu from comment #8) > ix86_expand_sse_fp_minmax failed since rtx_equal_p (cmp_op0, if_true) is > false, > > 249(reg:DF 86 [ _1 ]) (if_true) > 250(reg:DF 83 [ _2 ]) (if_false) > 251(reg:DF 82 [ _1 ]) (cmp0_op0) > 252(reg:DF 83 [ _2 ]) (cmp1_op1) > > but here if_true is just a copy from cmp_op0 but with different REGNO, > rtx_equal_p seems too conservative here. > But if_convert didn't maintain DF_CHAIN info, and and backend can't get DF_REG_DEF_* info to figure out if_true is just a single_set of cmp_op0. With -march=x86-64-v2, gcc generates movsd (%rdi), %xmm2 movsd (%rsi), %xmm1 movapd %xmm2, %xmm0 movapd %xmm1, %xmm3 cmpltsd %xmm1, %xmm0 maxsd %xmm2, %xmm3 blendvpd%xmm0, %xmm2, %xmm1 movsd %xmm3, (%rsi) movsd %xmm1, (%rdi) ret Which can be further optimized: cmpltsd + blendvpd -> minsd
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170
--- Comment #8 from Hongtao.liu ---
ix86_expand_sse_fp_minmax failed since rtx_equal_p (cmp_op0, if_true) is false,
249(reg:DF 86 [ _1 ]) (if_true)
250(reg:DF 83 [ _2 ]) (if_false)
251(reg:DF 82 [ _1 ]) (cmp0_op0)
252(reg:DF 83 [ _2 ]) (cmp1_op1)
but here if_true is just a copy from cmp_op0 but with different REGNO,
rtx_equal_p seems too conservative here.
85(code_label 26 13 17 3 4 (nil) [1 uses])
86(note 17 26 5 3 [bb 3] NOTE_INSN_BASIC_BLOCK)
87(insn 5 17 6 3 (set (reg:DF 86 [ _1 ])
88(reg:DF 82 [ _1 ])) "test.C":3:20 153 {*movdf_internal}
89 (expr_list:REG_DEAD (reg:DF 82 [ _1 ])
90(nil)))
91(insn 6 5 7 3 (set (reg:DF 82 [ _1 ])
92(reg:DF 83 [ _2 ])) "test.C":4:14 discrim 1 153 {*movdf_internal}
93 (expr_list:REG_DEAD (reg:DF 83 [ _2 ])
94(nil)))
95(insn 7 6 18 3 (set (reg:DF 83 [ _2 ])
96(reg:DF 86 [ _1 ])) "test.C":3:20 discrim 1 153 {*movdf_internal}
97 (expr_list:REG_DEAD (reg:DF 86 [ _1 ])
98(nil)))
3812 if (rtx_equal_p (cmp_op0, if_true) && rtx_equal_p (cmp_op1, if_false))
3813is_min = true;
3814 else if (rtx_equal_p (cmp_op1, if_true) && rtx_equal_p (cmp_op0,
if_false))
3815is_min = false;
3816 else
3817=> return false;
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 Richard Biener changed: What|Removed |Added Status|UNCONFIRMED |NEW Ever confirmed|0 |1 Last reconfirmed||2023-06-09
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170
--- Comment #7 from Hongtao.liu ---
void __cond_swap(double* __x, double* __y) {
bool __r = (*__x < *__y);
*__x = __r ? *__y : *__x ;
}
void __cond_swap1(double* __x, double* __y) {
bool __r = (*__x < *__y);
*__y = __r ? *__x : *__y;
}
Separately, GCC can generate both max/min.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 --- Comment #6 from Hongtao.liu --- (In reply to Hongtao.liu from comment #5) > (In reply to Antony Polukhin from comment #2) > > -fno-trapping-math had no effect > > > > Some tests with nans seem to produce the same results for both code > > snippets: https://godbolt.org/z/GaKM3EhMq > > What about infinity, I notice > With -ffinite-math-only -funsafe-math-optimizations, gcc now can generate > > __cond_swap(double*, double*): > movsd (%rdi), %xmm0 > movsd (%rsi), %xmm1 > movapd %xmm0, %xmm2 > minsd %xmm1, %xmm0 > maxsd %xmm1, %xmm2 > movsd %xmm2, (%rsi) > movsd %xmm0, (%rdi) > ret Assume -funsafe-math-optimizations is not needed?
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 --- Comment #5 from Hongtao.liu --- (In reply to Antony Polukhin from comment #2) > -fno-trapping-math had no effect > > Some tests with nans seem to produce the same results for both code > snippets: https://godbolt.org/z/GaKM3EhMq What about infinity, I notice With -ffinite-math-only -funsafe-math-optimizations, gcc now can generate __cond_swap(double*, double*): movsd (%rdi), %xmm0 movsd (%rsi), %xmm1 movapd %xmm0, %xmm2 minsd %xmm1, %xmm0 maxsd %xmm1, %xmm2 movsd %xmm2, (%rsi) movsd %xmm0, (%rdi) ret
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170
Andrew Pinski changed:
What|Removed |Added
Target||x86_64-linux-gnu
--- Comment #4 from Andrew Pinski ---
Note for aarch64, we do produce conditional moves but only when there is a
loop.
That is:
```
__attribute__((noinline))
void __cond_swap(double* __x, double* __y) {
for(int i = 0; i < 100; i++, __x++, __y++) {
double __r = (*__x < *__y);
double __tmp = __r ? *__x : *__y;
*__y = __r ? *__y : *__x;
*__x = __tmp;
}
}
```
Produces:
```
.L3:
ldr d31, [x0, x2]
ldr d30, [x1, x2]
fcmpe d31, d30
fcsel d29, d30, d31, mi
fcsel d31, d31, d30, mi
str d29, [x1, x2]
str d31, [x0, x2]
add x2, x2, 8
cmp x2, 800
bne .L3
```
Otherwise it will duplicate the return basic block (which is expected).
So this is a x86_64 specific issue.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 --- Comment #3 from Andrew Pinski --- So for arm, GCC does produce the code you want: ``` vcmpe.f64 d17, d16 vmrsAPSR_nzcv, FPSCR ite pl vmovpl.f64 d18, d17 vmovmi.f64 d18, d16 it mi vmovmi.f64 d16, d17 ``` RTL CE1 (ifcvt) detects it: if-conversion succeeded through noce_convert_multiple_sets So maybe there is some cost issue. Because arm64 does not do it either.
[Bug target/110170] Sub-optimal conditional jumps in conditional-swap with floating point
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110170 --- Comment #2 from Antony Polukhin --- -fno-trapping-math had no effect Some tests with nans seem to produce the same results for both code snippets: https://godbolt.org/z/GaKM3EhMq
