https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115095
Bug ID: 115095
Summary: [missed optimization] fixed processing on constant
string
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: yann at droneaud dot fr
Target Milestone: ---
Created attachment 58208
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58208&action=edit
source code of https://godbolt.org/z/Meqvbj8GG
I've found clang was able to compute the result of hashing a constant string at
compile time. I would have hope GCC -O3 would be able to optimize such
computation as well:
static inline unsigned int hash(unsigned int h, const char *s)
{
while (*s) {
h += *s;
h *= *s++;
}
return h;
}
#define LOCATION() hash(hash(0, __FILE__), __func__)
unsigned int location(void)
{
return LOCATION();
}
is translated by clang to
location:
movl $1418535820, %eax
retq
but not by GCC, which doesn't compute the value of LOCATION() at compile time
but emit code that compute the value at runtime.
At first, I thought it was an issue with handling __FILE__ or __func__, but
trying with other string constants, GCC is not computing the value at compile
time.
See https://godbolt.org/z/Meqvbj8GG
