https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103696
Bug ID: 103696
Summary: Lambda functions are not inlined under certain
optimization pragmas
Product: gcc
Version: 11.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: imachug at gmail dot com
Target Milestone: ---
This seems like a very weird bug to me and I'm not even sure how to label it,
so please fix the component if needed.
Testcase (C++):
#pragma GCC optimize("finite-math-only")
#pragma GCC target("sse3")
void fn() {
}
int global_var;
int solve() {
auto nested = []() {
return global_var;
};
return nested();
}
When compiling this code via `g++ test.cpp -c -O2 -std=c++17`, I get the
following assembly:
$ objdump -d test.o
...
0000000000000000 <_ZZ5solvevENKUlvE_clEv.constprop.0>:
0: 8b 05 00 00 00 00 mov 0x0(%rip),%eax # 6
<_ZZ5solvevENKUlvE_clEv.constprop.0+0x6>
6: c3 retq
7: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1)
e: 00 00
...
0000000000000020 <_Z5solvev>:
20: f3 0f 1e fa endbr64
24: e8 d7 ff ff ff callq 0 <_ZZ5solvevENKUlvE_clEv.constprop.0>
29: c3 retq
As you can see, the nested() lambda call was not inlined into solve().
However, if I do any of the following, the lambda is inlined as expected:
- Remove `fn` definition
- Move `fn` definition under `solve`
- Replace reading `global_var` with a constant
- Make `nested` a global function
- Remove either of the two pragmas (or both)
- Add -ffinite-math-only or -msse3 or both to the compilation line (regardless
of whether the pragmas are still there)
I have absolutely no idea why a floating point optimization affects inlining or
how a pragma is different from a compilation line option wrt. this bug.
