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* [Bug ipa/105193] New: Code divergence based on -fdump-tree-* since r9-5080-gf7293b9dfab5e6e7
@ 2022-04-07 9:43 marxin at gcc dot gnu.org
2022-04-07 9:44 ` [Bug ipa/105193] " marxin at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: marxin at gcc dot gnu.org @ 2022-04-07 9:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105193
Bug ID: 105193
Summary: Code divergence based on -fdump-tree-* since
r9-5080-gf7293b9dfab5e6e7
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ipa
Assignee: unassigned at gcc dot gnu.org
Reporter: marxin at gcc dot gnu.org
CC: hubicka at gcc dot gnu.org, marxin at gcc dot gnu.org
Target Milestone: ---
The following code diverges:
$ cat NodeImpl.ii
struct NodeImpl {
virtual bool isAttrImpl();
void deleteIf();
virtual int getOwnerDocument();
void unreferenced();
bool isOwned();
};
struct AttrImpl : NodeImpl {
bool isAttrImpl();
};
bool NodeImpl::isAttrImpl() { return false; }
NodeImpl *deleteIf_thisNode;
void NodeImpl::deleteIf() {
if (isOwned())
return;
isAttrImpl();
((AttrImpl *)deleteIf_thisNode)->getOwnerDocument();
}
void NodeImpl::unreferenced() { deleteIf(); }
$ g++ -O2 NodeImpl.ii -c -S -o 1.s -fdump-tree-all=/dev/null && g++ -O2
NodeImpl.ii -c -S -o 2.s && diff -u [12].s
--- 1.s 2022-04-07 11:43:05.995744783 +0200
+++ 2.s 2022-04-07 11:43:06.023744659 +0200
@@ -27,8 +27,10 @@
testb %al, %al
jne .L3
movq 0(%rbp), %rax
- movq %rbp, %rdi
- call *(%rax)
+ movq (%rax), %rax
+ cmpq $_ZN8NodeImpl10isAttrImplEv, %rax
+ jne .L10
+.L5:
movq deleteIf_thisNode(%rip), %rdi
popq %rbp
.cfi_remember_state
@@ -41,8 +43,16 @@
.L3:
.cfi_restore_state
popq %rbp
+ .cfi_remember_state
.cfi_def_cfa_offset 8
ret
+ .p2align 4,,10
+ .p2align 3
+.L10:
+ .cfi_restore_state
+ movq %rbp, %rdi
+ call *%rax
+ jmp .L5
.cfi_endproc
.LFE1:
.size _ZN8NodeImpl8deleteIfEv, .-_ZN8NodeImpl8deleteIfEv
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug ipa/105193] Code divergence based on -fdump-tree-* since r9-5080-gf7293b9dfab5e6e7
2022-04-07 9:43 [Bug ipa/105193] New: Code divergence based on -fdump-tree-* since r9-5080-gf7293b9dfab5e6e7 marxin at gcc dot gnu.org
@ 2022-04-07 9:44 ` marxin at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: marxin at gcc dot gnu.org @ 2022-04-07 9:44 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105193
Martin Liška <marxin at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2022-04-07
Ever confirmed|0 |1
--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
It's speculative devirtualization that plays the role:
$ g++ -O2 NodeImpl.ii -c -S -o 1.s -fdump-tree-all=/dev/null
-fdump-tree-optimized=1 && g++ -O2 NodeImpl.ii -c -S -o 2.s
-fdump-tree-optimized=2 && diff -u 1 2
--- 1 2022-04-07 11:43:51.739540416 +0200
+++ 2 2022-04-07 11:43:51.767540290 +0200
@@ -12,7 +12,8 @@
;; Function NodeImpl::deleteIf (_ZN8NodeImpl8deleteIfEv, funcdef_no=1,
decl_uid=2352, cgraph_uid=2, symbol_order=2)
-Removing basic block 5
+Removing basic block 7
+Removing basic block 8
void NodeImpl::deleteIf (struct NodeImpl * const this)
{
bool _6;
@@ -22,25 +23,35 @@
struct NodeImpl * _10;
int (*) () * _11;
int (*) () _12;
+ void * PROF_13;
<bb 2> [local count: 1073741824]:
_6 = NodeImpl::isOwned (this_4(D));
if (_6 != 0)
- goto <bb 4>; [34.00%]
+ goto <bb 6>; [34.00%]
else
goto <bb 3>; [66.00%]
<bb 3> [local count: 708669601]:
_7 = this_4(D)->_vptr.NodeImpl;
_8 = *_7;
+ PROF_13 = [obj_type_ref] OBJ_TYPE_REF(_8;(struct NodeImpl)this_4(D)->0);
+ if (PROF_13 == isAttrImpl)
+ goto <bb 5>; [80.00%]
+ else
+ goto <bb 4>; [20.00%]
+
+ <bb 4> [local count: 141733922]:
OBJ_TYPE_REF(_8;(struct NodeImpl)this_4(D)->0) (this_4(D));
+
+ <bb 5> [local count: 708669601]:
deleteIf_thisNode.1_9 = deleteIf_thisNode;
_10 = &MEM[(struct AttrImpl *)deleteIf_thisNode.1_9].D.2378;
_11 = MEM[(struct AttrImpl *)deleteIf_thisNode.1_9].D.2378._vptr.NodeImpl;
_12 = MEM[(int (*) () *)_11 + 8B];
OBJ_TYPE_REF(_12;(struct NodeImpl)_10->1) (_10); [tail call]
- <bb 4> [local count: 1073741824]:
+ <bb 6> [local count: 1073741824]:
return;
}
^ permalink raw reply [flat|nested] 2+ messages in thread
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2022-04-07 9:43 [Bug ipa/105193] New: Code divergence based on -fdump-tree-* since r9-5080-gf7293b9dfab5e6e7 marxin at gcc dot gnu.org
2022-04-07 9:44 ` [Bug ipa/105193] " marxin at gcc dot gnu.org
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