[Bug ipa/93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC -fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115
--- Comment #8 from Sergei Trofimovich ---
Slightly better example without warnings (used `__builtin_trap();` to work
around use of uninitialized value):
```c++
struct a {
char ac1;
char ac2;
int d() { return av() + ac1 + ac2; }
virtual void f() {}
virtual int av() { __builtin_trap(); }
a(){}
};
struct g : a {
virtual void f2();
g():a(){}
};
#ifdef LIB_FILE
void g::f2() {}
#endif
#ifdef MAIN_FILE
static g b;
static char bb;
char cc() { return bb; }
void h() {
if (cc()) {
b.d();
return;
}
}
int main() {}
#endif
```
[Bug ipa/93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC -fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115
--- Comment #7 from Sergei Trofimovich ---
Looks like original test does not trigger the bug as is (probably due to tets
fragility). Here is something shorter (but with warnings):
```c++
struct a {
char at;
char au;
int d() { return av() + au - at; }
virtual void f() {}
virtual int av() { }
};
struct g : a {
void f();
char b;
char c() { return b; }
} b;
#ifdef MAIN_FILE
g e;
void h() {
if (b.c()) {
e.d();
return;
}
}
int main() {}
#endif
#ifdef LIB_FILE
void g::f() {}
#endif
```
$ g++-11.0.0 -Wall -fPIC -O1 -fdevirtualize -fdevirtualize-speculatively
-fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden -fPIC -shared -o libbug.so
bug.cpp -DLIB_FILE
bug.cpp: In member function 'virtual int a::av()':
bug.cpp:6:22: warning: no return statement in function returning non-void
[-Wreturn-type]
6 | virtual int av() { }
| ^
$ g++-11.0.0 -Wall -fPIC -O1 -fdevirtualize -fdevirtualize-speculatively
-fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden -o main bug.cpp -DMAIN_FILE
-L. -lbug
bug.cpp: In member function 'virtual int a::av()':
bug.cpp:6:22: warning: no return statement in function returning non-void
[-Wreturn-type]
6 | virtual int av() { }
| ^
/usr/lib/gcc/x86_64-pc-linux-gnu/11.0.0/../../../../x86_64-pc-linux-gnu/bin/ld:
/tmp/ccbaHYef.o: in function `h()':
bug.cpp:(.text+0x1a): undefined reference to `a::av()'
collect2: error: ld returned 1 exit status
[Bug ipa/93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC -fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115 Sergei Trofimovich changed: What|Removed |Added CC||slyfox at gcc dot gnu.org --- Comment #6 from Sergei Trofimovich --- Still happens with gcc-11.
[Bug ipa/93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC -fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115 Richard Biener changed: What|Removed |Added Keywords||wrong-code Target Milestone|10.0|---
[Bug ipa/93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC -fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115 Jan Hubicka changed: What|Removed |Added CC||mjambor at suse dot cz --- Comment #5 from Jan Hubicka --- OK, the missed optimization follows from the following: 1) ipa-cp creates specialized node for o. It is called only once from fn3 p calls unspecialized o. I wonder why this happens since both calls in p and fn3 leads to devirtualization. 2) inliner inlines k to o. This does not enable devirtualization because o is not specialized. 3) at the end of inlining remove_unreachable_nodes removes the offiline copy of m::av 4) we inline o to p enabling devirtualization but it is too late. Adding inline keyword to p makes inliner to inline it early but we still miss the devirutalization. So we have two issues a) for some reason ipa-cp rules out reasonable specialization I it is decided here: Evaluating opportunities for void o(j&)/11. - considering value for param #0 p1 (caller_count: 1) good_cloning_opportunity_p (time: 1, size: 36, freq_sum: 1000) -> evaluation: 27, threshold: 500 good_cloning_opportunity_p (time: 199, size: 120, freq_sum: 1000) -> evaluation: 1658, threshold: 500 Creating a specialized node of void o(j&)/11. the new node is o.constprop/37. known ctx 0 is Outer type:struct j offset 0 - considering value for param #0 p1 (caller_count: 1) good_cloning_opportunity_p (time: 1, size: 36, freq_sum: 202) -> evaluation: 5, threshold: 500 good_cloning_opportunity_p (time: 103, size: 120, freq_sum: 202) -> evaluation: 173, threshold: 500 I assume it is because freq_sum is 202 instead of 1000 because call is conditional, but that is really way too strict... 20% is outcome of: Predictions for bb 2 DS theory heuristics: 20.24% combined heuristics: 20.24% call heuristics of edge 2->3: 33.00% early return (on trees) heuristics of edge 2->3: 34.00% Predictions for bb 3 which seems reasonable. b) we do not devirtualize after inlining. We combine context correctly: Polymorphic call context combine:Speculative outer type:struct j (or a derived type) at offset 0 With context:Outer type:struct m offset 0 Updated as: Outer type:struct m offset 0 Speculative outer type:struct j (or a derived type) at offset 0 but I am not sure why it does not trigger devirt at this stage. We also do not need to have speculative outer type when we know outer type precisely, but it is cosmetic issue.
[Bug ipa/93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC -fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115
--- Comment #4 from Jan Hubicka ---
The problem here is that we produce ipa-cp clone to devirtualize v::av which
also lead to devirtualization of m::av, but we miss this optimization. After
inlining we remove m::av and while producing the ipa-cp clone we devirtualize
to it which elads to undefined reference.
I am testing the following:
Index: ipa.c
===
--- ipa.c (revision 279810)
+++ ipa.c (working copy)
@@ -187,6 +187,7 @@ walk_polymorphic_call_targets (hash_set<
for (i = 0; i < targets.length (); i++)
{
struct cgraph_node *n = targets[i];
+ bool added = false;
/* Do not bother to mark virtual methods in anonymous namespace;
either we will find use of virtual table defining it, or it is
@@ -212,11 +213,18 @@ walk_polymorphic_call_targets (hash_set<
&& symtab->state < IPA_SSA_AFTER_INLINING)
reachable->add (body);
reachable->add (n);
+ added = true;
}
/* Even after inlining we want to keep the possible targets in the
boundary, so late passes can still produce direct call even if
-the chance for inlining is lost. */
- enqueue_node (n, first, reachable);
+the chance for inlining is lost.
+Do not keep references to comdat groups - removing their
definition
+first and adding references later is going to give undefined
+reference errors. */
+ if (added || (!DECL_COMDAT (n->decl)
+ || DECL_EXTERNAL (n->decl)
+ || !TREE_PUBLIC (n->decl)))
+ enqueue_node (n, first, reachable);
}
}
[Bug ipa/93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC -fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115 Martin Liška changed: What|Removed |Added Status|UNCONFIRMED |ASSIGNED Last reconfirmed||2020-01-02 Assignee|unassigned at gcc dot gnu.org |hubicka at gcc dot gnu.org Target Milestone|--- |10.0 Ever confirmed|0 |1 --- Comment #3 from Martin Liška --- I can confirm it. If I see correctly, it started on trunk with r276416. I can't reproduce it on GCC 9 branch (neither with GCC 9.2.0 release).
[Bug ipa/93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC -fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115 --- Comment #2 from Sergei Trofimovich --- bug.cpp is a trimmed down version of llvm-roc's codebase with creduce.
[Bug ipa/93115] gcc fails to emit inline function on llvm-roc project: -O1 -fPIC -fdevirtualize -fdevirtualize-speculatively -fipa-cp -fipa-cp-clone -fvisibility-inlines-hidden
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93115 Sergei Trofimovich changed: What|Removed |Added Target||x86_64-pc-linux-gnu CC||0xe2.0x9a.0x9b at gmail dot com, ||hubicka at gcc dot gnu.org --- Comment #1 from Sergei Trofimovich --- I've built gcc-master as: $ ./xg++ -v Using built-in specs. COLLECT_GCC=./xg++ Target: x86_64-pc-linux-gnu Configured with: ../gcc/configure --enable-languages=c,c++ --disable-bootstrap --with-multilib-list=m64 --prefix=/home/slyfox/dev/git/gcc-clean/../gcc-native-quick-installed --disable-nls --without-isl --disable-libsanitizer --disable-libvtv --disable-libgomp --disable-libstdcxx-pch --disable-libunwind-exceptions CFLAGS='-O1 ' CXXFLAGS='-O1 ' --with-sysroot=/usr/x86_64-HEAD-linux-gnu Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 10.0.0 20200101 (experimental) (GCC)
