https://bugs.llvm.org/show_bug.cgi?id=38335
Bug ID: 38335
Summary: Missed optimization of functions deduplication
Product: clang
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: C++
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
If two functions have the same body Clang does not deduplicate the functions.
Consider the following example:
void mutate0(int&);
template <int I>
int foo_template(int b) {
mutate0(b); mutate0(b); mutate0(b); mutate0(b);
mutate0(b); mutate0(b); mutate0(b); mutate0(b);
mutate0(b); mutate0(b); mutate0(b); mutate0(b);
return b;
}
int foo0(int b) {
return foo_template<0>(b);
}
int foo1(int b) {
return foo_template<1>(b);
}
GCC deduplicates the function bodies and foo1 and foo2 and call the same
template instantiation:
_Z4foo0i:
jmp _Z12foo_templateILi0EEii
_Z4foo1i:
jmp _Z12foo_templateILi0EEii # Same as above
Clang instead produces functions that call different template instantiations:
_Z4foo0i:
jmp _Z12foo_templateILi0EEii
_Z4foo1i:
jmp _Z12foo_templateILi1EEii # Differs from above!
This results in a two times bigger assembly on Clang.
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