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* [Bug tree-optimization/111293] New: [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
@ 2023-09-05 15:01 theodort at inf dot ethz.ch
2023-09-05 17:25 ` [Bug tree-optimization/111293] " pinskia at gcc dot gnu.org
` (7 more replies)
0 siblings, 8 replies; 9+ messages in thread
From: theodort at inf dot ethz.ch @ 2023-09-05 15:01 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293
Bug ID: 111293
Summary: [14 Regression] Missed Dead Code Elimination since
r14-3414-g0cfc9c953d0
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: theodort at inf dot ethz.ch
Target Milestone: ---
https://godbolt.org/z/9aj7sr5d6
Given the following code:
void foo(void);
static int a, d;
static short e;
static int(f)(int b, int c) { return c == 0 ? b : b / c; }
static char g(char h) {
char i = 1;
int j = 8;
e = 3;
for (; d; ++d) {
if (f(0 == j, e)) return a;
for (; i; i--) {
if (j) {
if (e)
;
else if (a)
continue;
else
foo();
j = -h;
break;
}
__builtin_unreachable();
break;
}
}
return 1;
}
int main() {
g(-1);
a = e;
}
gcc-trunk -O2 does not eliminate the call to foo:
main:
subq $8, %rsp
movl d(%rip), %ecx
movl $3, %edx
movw %dx, e(%rip)
testl %ecx, %ecx
je .L6
movl $3, %edx
.p2align 4,,10
.p2align 3
.L2:
testw %dx, %dx
jne .L3
movl a(%rip), %eax
testl %eax, %eax
je .L18
.L5:
addl $1, d(%rip)
jne .L5
.L6:
movswl e(%rip), %eax
movl %eax, a(%rip)
xorl %eax, %eax
addq $8, %rsp
ret
.p2align 4,,10
.p2align 3
.L18:
call foo
.L3:
addl $1, d(%rip)
movzwl e(%rip), %edx
jne .L2
jmp .L6
gcc-13.2.0 -O2 eliminates the call to foo:
main:
movl d(%rip), %edx
movl $3, %eax
movw %ax, e(%rip)
testl %edx, %edx
je .L3
movl $0, d(%rip)
.L3:
movl $3, a(%rip)
xorl %eax, %eax
ret
Bisects to r14-3414-g0cfc9c953d0
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
2023-09-05 15:01 [Bug tree-optimization/111293] New: [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0 theodort at inf dot ethz.ch
@ 2023-09-05 17:25 ` pinskia at gcc dot gnu.org
2023-09-05 17:40 ` pinskia at gcc dot gnu.org
` (6 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-09-05 17:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Target Milestone|--- |14.0
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
2023-09-05 15:01 [Bug tree-optimization/111293] New: [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0 theodort at inf dot ethz.ch
2023-09-05 17:25 ` [Bug tree-optimization/111293] " pinskia at gcc dot gnu.org
@ 2023-09-05 17:40 ` pinskia at gcc dot gnu.org
2023-09-05 17:40 ` pinskia at gcc dot gnu.org
` (5 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-09-05 17:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The difference is the trunk can figure out the range for j_8:
PHI GROUP query for j_8 found : [irange] int [1, 1][8, 8] and adjusted original
range from :[irange] int [1, 1][8, 8] to :[irange] int [1, 1][8, 8]
Global Exported: j_8 = [irange] int [1, 1][8, 8] MASK 0x9 VALUE 0x8
But 13 can't:
Global Exported: j_8 = [irange] int [-INF, +INF] NONZERO 0x9
I have not looked into how 13 can remove the call to foo though.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
2023-09-05 15:01 [Bug tree-optimization/111293] New: [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0 theodort at inf dot ethz.ch
2023-09-05 17:25 ` [Bug tree-optimization/111293] " pinskia at gcc dot gnu.org
2023-09-05 17:40 ` pinskia at gcc dot gnu.org
@ 2023-09-05 17:40 ` pinskia at gcc dot gnu.org
2023-11-24 15:56 ` amacleod at redhat dot com
` (4 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-09-05 17:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Last reconfirmed| |2023-09-05
Status|UNCONFIRMED |NEW
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
2023-09-05 15:01 [Bug tree-optimization/111293] New: [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0 theodort at inf dot ethz.ch
` (2 preceding siblings ...)
2023-09-05 17:40 ` pinskia at gcc dot gnu.org
@ 2023-11-24 15:56 ` amacleod at redhat dot com
2024-03-07 23:21 ` law at gcc dot gnu.org
` (3 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: amacleod at redhat dot com @ 2023-11-24 15:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293
--- Comment #2 from Andrew Macleod <amacleod at redhat dot com> ---
It seems like we set 'e' to 3 immediately at the start:
<bb 2> [local count: 1073741824]:
e = 3;
goto <bb 10>; [100.00%]
and it is never changed again. However, when we load from 'e' later in the IL
<bb 3> [local count: 9485263241]:
e.1_6 = e;
we simply get varying. Is some pass suppose to propagate this? This reminds me
of a few other regression PRs where we no longer propagate known values from
loads from memory into ssa-names.
If we knew that e.1_6 was '3', then the call to foo would be folded away as
never executable.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
2023-09-05 15:01 [Bug tree-optimization/111293] New: [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0 theodort at inf dot ethz.ch
` (3 preceding siblings ...)
2023-11-24 15:56 ` amacleod at redhat dot com
@ 2024-03-07 23:21 ` law at gcc dot gnu.org
2024-04-09 9:38 ` mikael at gcc dot gnu.org
` (2 subsequent siblings)
7 siblings, 0 replies; 9+ messages in thread
From: law at gcc dot gnu.org @ 2024-03-07 23:21 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293
Jeffrey A. Law <law at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Priority|P3 |P2
CC| |law at gcc dot gnu.org
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
2023-09-05 15:01 [Bug tree-optimization/111293] New: [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0 theodort at inf dot ethz.ch
` (4 preceding siblings ...)
2024-03-07 23:21 ` law at gcc dot gnu.org
@ 2024-04-09 9:38 ` mikael at gcc dot gnu.org
2024-04-09 9:47 ` mikael at gcc dot gnu.org
2024-05-07 7:41 ` [Bug tree-optimization/111293] [14/15 " rguenth at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: mikael at gcc dot gnu.org @ 2024-04-09 9:38 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293
Mikael Morin <mikael at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |mikael at gcc dot gnu.org
--- Comment #3 from Mikael Morin <mikael at gcc dot gnu.org> ---
pre replaces usages of the 'e' global with a set of 'pretmp' and 'prephitmp'
ssa registers.
With gcc-13, the value of 'e' is reloaded directly after the call to 'foo',
and that value is joined with a phi in the next bb:
<bb 10> [local count: 7761689018]:
foo ();
pretmp_25 = e;
goto <bb 15>; [100.00%]
...
<bb 15> [local count: 8963573811]:
# j_28 = PHI <1(10), j_30(24), 1(22), j_30(25), 1(26), j_30(20)>
# i_29 = PHI <i_20(10), 0(24), i_19(22), 0(25), i_21(26), 0(20)>
# prephitmp_38 = PHI <pretmp_25(10), prephitmp_26(24), prephitmp_26(22),
prephitmp_26(25), prephitmp_26(26), prephitmp_26(20)>
d.7_22 = d;
_23 = d.7_22 + 1;
d = _23;
if (_23 != 0)
goto <bb 27>; [94.50%]
else
goto <bb 18>; [5.50%]
With gcc-14, the value of 'e' is reloaded later in the next bb, causing a
dependency on 'e', even on paths not calling 'foo':
<bb 5> [local count: 7761689018]:
foo ();
goto <bb 8>; [100.00%]
...
<bb 8> [local count: 8963573796]:
# i_28 = PHI <i_13(5), 0(12), i_13(15)>
d.7_22 = d;
_23 = d.7_22 + 1;
d = _23;
pretmp_10 = e;
if (_23 != 0)
goto <bb 17>; [94.50%]
else
goto <bb 11>; [5.50%]
Later on this prevents copyprop from simplifying the 'pretmp' and 'prephitmp'
values to 3 and remove the branch calling 'foo'.
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
2023-09-05 15:01 [Bug tree-optimization/111293] New: [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0 theodort at inf dot ethz.ch
` (5 preceding siblings ...)
2024-04-09 9:38 ` mikael at gcc dot gnu.org
@ 2024-04-09 9:47 ` mikael at gcc dot gnu.org
2024-05-07 7:41 ` [Bug tree-optimization/111293] [14/15 " rguenth at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: mikael at gcc dot gnu.org @ 2024-04-09 9:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293
--- Comment #4 from Mikael Morin <mikael at gcc dot gnu.org> ---
For what's worth adding -fno-tree-vrp "fixes" this and enables removal of the
call to 'foo' with trunk.
Here is a minimal revert of the regressing revision, but it may just make the
problem latent.
diff --git a/gcc/gimple-range-phi.cc b/gcc/gimple-range-phi.cc
index 01900a35b32..9fa9fe83ce0 100644
--- a/gcc/gimple-range-phi.cc
+++ b/gcc/gimple-range-phi.cc
@@ -386,14 +386,6 @@ phi_analyzer::process_phi (gphi *phi)
m_work.safe_push (arg);
continue;
}
- // More than 2 outside names is too complicated.
- if (m_num_extern >= 2)
- {
- cycle_p = false;
- break;
- }
- m_external[m_num_extern] = arg;
- m_ext_edge[m_num_extern++] = gimple_phi_arg_edge (phi_stmt, x);
}
else if (code == INTEGER_CST)
{
@@ -402,12 +394,15 @@ phi_analyzer::process_phi (gphi *phi)
wi::to_wide (arg));
init_range.union_ (val);
}
- else
+ // More than 2 outside names/CONST is too complicated.
+ if (m_num_extern >= 2)
{
- // Everything else terminates the cycle.
cycle_p = false;
break;
}
+
+ m_external[m_num_extern] = arg;
+ m_ext_edge[m_num_extern++] = gimple_phi_arg_edge (phi_stmt, x);
}
}
^ permalink raw reply [flat|nested] 9+ messages in thread
* [Bug tree-optimization/111293] [14/15 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0
2023-09-05 15:01 [Bug tree-optimization/111293] New: [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0 theodort at inf dot ethz.ch
` (6 preceding siblings ...)
2024-04-09 9:47 ` mikael at gcc dot gnu.org
@ 2024-05-07 7:41 ` rguenth at gcc dot gnu.org
7 siblings, 0 replies; 9+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-05-07 7:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|14.0 |14.2
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 14.1 is being released, retargeting bugs to GCC 14.2.
^ permalink raw reply [flat|nested] 9+ messages in thread
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2023-09-05 15:01 [Bug tree-optimization/111293] New: [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0 theodort at inf dot ethz.ch
2023-09-05 17:25 ` [Bug tree-optimization/111293] " pinskia at gcc dot gnu.org
2023-09-05 17:40 ` pinskia at gcc dot gnu.org
2023-09-05 17:40 ` pinskia at gcc dot gnu.org
2023-11-24 15:56 ` amacleod at redhat dot com
2024-03-07 23:21 ` law at gcc dot gnu.org
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